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CONFALONIERI, GIORGIA. "LOCAL DISORDER IN THE STRUCTURE OF BA(TI,CE)O3 PEROVSKITE BY MEANS OF POWDER DIFFRACTION AND TOTAL SCATTERING. EFFECT OF TEMPERATURE, DOPING CONCENTRATION AND GRAIN SIZE." Doctoral thesis, Università degli Studi di Milano, 2017. http://hdl.handle.net/2434/478906.
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Nowadays BaTiO3 is considered as one of the most relevant environmental-friend ferroelectric and, thank to the chemical substitutions at the Ba2+ and/or Ti4+ sites, its properties are usually tailor to meet a big variety of devices and performance requirements. A classical example is the solid solution BaTi1-xMIVxO3, where M could be Sn, Zr, Hf, Ce etc., whose ferroelectric behavior shows an almost continuous variation with composition. The study of these compounds is then essential to improve their characteristics and make their suitable in more applications. Considering that their properties are deeply linked to the structure and especially to structural defects, average and local structural analyses are essential to better understand the origins of different polar behaviours and to have a real control on these materials. Despite this need, only BaTi1-xZrxO3 (BTZ) system, which is one of the most popular dielectrics used in multilayer ceramic capacitors, has been investigated in some detail. Although the similarity to BTZ suggests that BaTi1-xCexO3 (BTC) may be promising as lead free actuator materials, studies on this solid solution are almost limited. Thus in this research the BTC solid solution has been structurally investigated in order to provide knowledge lacks. Different ceramic samples with different doping amounts and different polar behaviours (from normal ferroelecric to relaxor via diffuse phase transition) have been investigated at different temperatures. In addition, taking into account the current tendency in miniaturized devices required in microelectronics, also chemical equivalent nano powders have been considered to explore not only doping effects, but also that of size. Pair Distribution Function (PDF) with different type of approaches (as carbox, biphasic and so on) has been employed coupled with TEM analysis and Raman spectroscopy. A complete description of that BaTi1-xCexO3 materials is given underlining links between polar behaviours, temperature, doping and size effects.
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Daza, Yolanda Andreina. "Closing a Synthetic Carbon Cycle: Carbon Dioxide Conversion to Carbon Monoxide for Liquid Fuels Synthesis." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6079.
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CO2 global emissions exceed 30 Giga tonnes (Gt) per year, and the high atmospheric concentrations are detrimental to the environment. In spite of efforts to decrease emissions by sequestration (carbon capture and storage) and repurposing (use in fine chemicals synthesis and oil extraction), more than 98% of CO2 generated is released to the atmosphere. With emissions expected to increase, transforming CO2 to chemicals of high demand could be an alternative to decrease its atmospheric concentration. Transportation fuels represent 26% of the global energy consumption, making it an ideal end product that could match the scale of CO2 generation. The long-term goal of the study is to transform CO2 to liquid fuels closing a synthetic carbon cycle.
Synthetic fuels, such as diesel and gasoline, can be produced from syngas (a combination of CO and H2) by Fischer Tropsch synthesis or methanol synthesis, respectively. Methanol can be turned into gasoline by MTO technologies. Technologies to make renewable hydrogen are already in existence, but CO is almost exclusively generated from methane. Due to the high stability of the CO2 molecule, its transformation is very energy intensive. Therefore, the current challenge is developing technologies for the conversion of CO2 to CO with a low energy requirement.
The work in this dissertation describes the development of a recyclable, isothermal, low-temperature process for the conversion of CO2 to CO with high selectivity, called Reverse Water Gas Shift Chemical Looping (RWGS-CL). In this process, H2 is used to generate oxygen vacancies in a metal oxide bed. These vacancies then can be re-filled by one O atom from CO2, producing CO. Perovskites (ABO3) were used as the oxide material due to their high oxygen mobility and stability. They were synthesized by the Pechini sol-gel synthesis, and characterized with X-ray diffraction and surface area measurements. Mass spectrometry was used to evaluate the reducibility and re-oxidation abilities of the materials with temperature-programmed reduction and oxidation experiments. Cycles of RWGS-CL were performed in a packed bed reactor to study CO production rates.
Different metal compositions on the A and B site of the oxide were tested. In all the studies, La and Sr were used on the A site because their combination is known to enhance oxygen vacancies formation and CO2 adsorption on the perovskites. The RWGS-CL was first demonstrated in a non-isothermal process at 500 °C for the H2-reduction and 850 °C for the CO2 conversion on a Co-based perovskite. This perovskite was too unstable for the H2 treatment. Addition of Fe to the perovskite enhanced its stability, and allowed for an isothermal and recyclable process at 550 °C with high selectivity towards CO. In an effort to decrease the operating temperature, Cu was incorporated to the structure. It was found that Cu addition inhibited CO formation and formed very unstable oxide materials.
Preliminary studies show that application of this technology has the potential to significantly reduce CO2 emissions from captured flue gases (i.e. from power plants) or from concentrated CO2 (adsorbed from the atmosphere), while generating a high value chemical. This technology also has possible applications in space explorations, especially in environments like Mars atmosphere, which has high concentrations of atmospheric carbon dioxide.
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Wirthová, Michaela. "Reologické vlastnosti gelů pro Pechiniho syntézy." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2009. http://www.nusl.cz/ntk/nusl-216509.
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This work deals with preparation of layers of ceramic materials – perovskites. The introductory part includes general characteristics concerning structure, properties and use of this materials. In details then there is described method of their preparation, namely Pechini´s syntheses, which are most widely used. Optimum molar ratio of components is discussed, in the sense of what compositions lead to creation of perovskite structures. Influence of this parameter on rheological properties of precursory gels is described in the end of the first part of work. In experimental section there are described preparations of gels, which are prepared via reaction between citric acid and ethylene glycol and gels, which are prepared by Pechini´s synthesis. Rheological properties of prepared gels (density, viscosity and surface tension) and besides determination of amount of nitrates in gels are characterized. Temperature dependence of viscosity of gels, that are prepared by reaction of citric acid and ethylene glycol are determined. In final part successful preparations of perovskite layers is shown on ceramic substrate. This layers are observed by means of light optical microscope and scanning electron microscope.
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Ljungström, Elin, Ellen Hådén, Lukas Lekberg, and Nima Taherpour. "Design, synthesis and characterization of Dimethylammonium / Ethylammonium / Cesium Lead Halide Perovskites for optoelectronic applications." Thesis, KTH, Skolan för kemi, bioteknologi och hälsa (CBH), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-277109.
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The world is facing a climate crisis and to be able to solve it society needs to decrease the use of fossil fuels and find renewable alternatives. Solar energy is a great contender for a renewable energy source since it can be harvested for eternal time. One of the problems with the solar cells available today is that they are more expensive than fossil alternatives, and the process of making them still uses a lot of resources and energy. However, in the last decade an alternative has arisen; perovskite solar cells. Due to the fact that perovskite solar cell production uses less energy and resources than the current silicon solar cell, perovskite solar cells are more cost effective. The main problem with perovskite solar cells is that they are too unstable and do not last very long. One way to stabilize them is to introduce one more cation and make hybrid perovskites. The purpose of this project was to synthesize a perovskite material with the chemical formula AA’PbI3 (A = Cs, A’ = dimethylammonium or ethylammonium) to see if any of the compositions would generate a stable black cubic phase, which is the optimal phase of the perovskite. Mesoporous N-I-P solar cells were created by a layer by layer deposition method. The perovskite layer was added using a spin-coater to deposit the perovskite solution. The films were then characterized using XRD and UV/Vis absorption spectroscopy. Due to the coronavirus pandemic of 2020, the hole transport material and gold electrode were not added to the solar cell. As a consequence of this, not all of the compositions were synthesised which also means that the results are not conclusive. It was observed that all of the films were yellow, which indicates that none of the perovskites achieved a cubic structure. An explanation could be that some parts of the synthesis needs to be done inside a glove box where the environmental variables like humidity could be controlled. The XRDs show that some films had the expected perovskite composition, while some perovskites had decomposed into its starting materials. For hybrid components and pure ethylammonium perovskite film it was harder to confirm our conclusion since no characterization of single crystals was available for these components. However, it was determined that the addition of cesium did make the perovskites more stable.
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Čižauskaitė, Sigutė. "Sol-gel synthesis of perovskite structure aluminates and cobaltates." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2009~D_20091202_112230-17664.
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In the present thesis the reported results let us to conclude that the developed aqueous sol–gel procedure could be successfully used for the low-temperature synthesis of monophasic perovskite gadolinium aluminate ceramics. It was also demonstrated that the selection of raw materials for the sol–gel processing should be done with care. Monophasic perovskite structure gadolinium aluminate GdAlO3 has been synthesized by sol gel synthesis method at 1000 oC, using gadolinium oxide as gadolinium raw material and 1.2 ethanediol, natural tartaric acid, citric acid or mixture of citric acid and ethanolamine as complexing agent. According to the XRD results, the Gd2O3 instead of Gd(NO3)36H2O preferably should be used as starting material for the preparation of GdAlO3. Monophasic perovskite structure strontium substituted gadolinium aluminate Gd0.90Sr0.10AlO3– was synthesized by the same sol gel synthesis method at 1000 oC, using gadolinium oxide as gadolinium raw material, strontium nitrate as strontium ion source and EDTA as complexing agent. It was proved that better gadolinium ion source is gadolinium oxide than gadolinium nitate hexahydrate, better complexing agent – EDTA than natural tartaric acid in the synthesis of GdAlO3 and strontium substituted Gd1–xSrxAlO3– (x = 0.10, 0.25, 0.50, 0.75) samples. According to the XRD results, increasing amount of strontium reduces amount of peaks of perovskite structure gadolinium aluminate. Besides, 800 ºC temperature is too low for the... [to full text]Šiame darbe vienfazis perovskito struktūros gadolinio aliuminatas GdAlO3 zolių-gelių metodu buvo gautas 1000 oC temperatūroje, gadolinio jonų šaltiniu naudojant Gd2O3, kompleksus sudarančiu reagentu – 1,2 etandiolį, natūralią vyno rūgštį, citrinų rūgštį arba citrinų rūgšties ir etanolamino mišinį. Sintetinant GdAlO3, gautų tyrimų rezultatai parodė, kaip yra svarbu zolių gelių procese pasirinkti tinkamas pradines medžiagas bei kompleksus su metalais sudarančius reagentus: gadolinio jonų šaltiniu naudojant Gd2O3 buvo gauti geresni rezultatai nei naudojant Gd(NO3)3•6H2O, vienfazis GdAlO3 gali būti sėkmingai susintetintas kompleksus sudarančiu reagentu naudojant tiek natūralią vyno rūgštį, tiek 1,2 etandiolį, tiek citrinų rūgštį, tiek citrinų rūgšties ir etanolamino mišinį. Nustatyta, kad sintetinant stronciu pakeistus gadolinio aliuminatus Gd1–xSrxAlO3– (x = 0,10, 0,25, 0,50, 0,75), tinkamesnis gadolinio jonų šaltinis yra gadolinio oksidas nei gadolinio nitratas heksahidratas, kompleksus sudarantis reagentas – EDTA nei natūrali vyno rūgštis. Vienfazis perovskito struktūros stronciu pakeistas gadolinio aliuminatas Gd0,90Sr0,10AlO3– buvo susintetintas zolių-gelių metodu 1000 oC temperatūroje, gadolinio jonų šaltiniu naudojant Gd2O3, stroncio jonų šaltiniu – Sr(NO3)2, kompleksus sudarančiu reagentu – EDTA. Be to, 800 ºC iškaitinimo temperatūra yra per maža šiems junginiams sintetinti. Pirmą kartą pasiūlytas vandeninis zolių gelių metodas lantano ir gadolinio kobaltatams... [toliau žr. visą tekstą]
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Liang, Xinxing. "Synthesis of perovskite nanocrystals and their applications in perovskite solar cells." Thesis, University of Bath, 2018. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.767584.
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Perovskite solar cells are a very promising photovoltaic technology which was first reported in 2009 and developed very rapidly. The crystallisation within perovskite films is highly dependent on processing environments, such as temperature, humidity, atmosphere, even light, which makes the fabrication of perovskite solar cells rather lab-dependent and poorly reproducible. One strategy to overcome this problem is to develop a controlled synthesis of perovskite nanocrystals which can then be ordered into films in a separatestep. In this thesis, optimisation of planar perovskite solar cells is carried out by the engineering of perovskite film fabrication methods. Different deposition methods along with different process factors such as solvents, temperature and precursor recipes are compared. One step spin-coating method with the recipe of MAI:PbCl2=3:1 gives the best PCE of 12.1 ± 0.7 % in air with controlled humidity of < 35%, showing high reliability and reproducibility. Doping of TiO2 layers with Zn2+, Sn4+ and Nb5+ ions are carried out to investigate the impacts of doping ions in different valence states on the electron-transporting properties of TiO2 ETLs. The different doping ions shift the flat band potential differently. Zn2+ largely negatively shifts the flat band potential, whereas Nb5+ positively shifts and Sn4+ barely changes the flat band potential of TiO2. the Zn-doping of the TiO2 ETL decreases the performance of the cells. However, when a thin layer of Zn-doped TiO2 is deposited on top of the pristine TiO2 layer as interlayer, the cell efficiency is slightly improved. Following the cell optimisation, to achieve better control over the crystallisation process, a facile flow reactor is developed for the synthesis of MAPbX3 perovskite nanocrystals at low temperature, which are further used for perovskite solar cells. The nanocrystals show narrow size distribution, good emissive properties and high stability. The bandgap of the nanocrystals was easily tuned between 485-745 nm by changing the halide composition. The photoluminescence of the MAPbI3 NCs in the first supernatant can also be tuned by changing the process parameters such as temperature, residence time and ligand concentration. However the impacts are more complex in the second supernatant in toluene with the appearance of multiple peaks in the PL spectra. It could be resultedfrom the formation of smaller NCs due to the reprecipitation of the incompletely removed reactants when added into toluene, or the fragmentation of the NCs upon dispersion into toluene, but better understanding is still needed. In the last part of the thesis, the synthesised MAPbI3 nanocrystals are investigated in perovskite solar cell applications. They have been applied as interlayers at the perovskite HTM interface, where they improved the stability of the devices towards moisture. The nanocrystals and their bulk by-products are also used as active light-absorbing layers for perovskite solar cells, delivering the best PCEs of 0.51% and 1.2% respectively, and notably showing outstanding water resistance. Further improvements in the cell performance could potentially be achieved by the removal of the insulating long chain ligands using effective ligand exchange treatments.
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Čižauskaitė, Sigutė. "Perovskito struktūros aliuminatų ir kobaltatų sintezė zolių-gelių metodu." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2009~D_20091202_112220-21150.
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Šiame darbe vienfazis perovskito struktūros gadolinio aliuminatas GdAlO3 zolių-gelių metodu buvo gautas 1000 oC temperatūroje, gadolinio jonų šaltiniu naudojant Gd2O3, kompleksus sudarančiu reagentu – 1,2 etandiolį, natūralią vyno rūgštį, citrinų rūgštį arba citrinų rūgšties ir etanolamino mišinį. Sintetinant GdAlO3, gautų tyrimų rezultatai parodė, kaip yra svarbu zolių gelių procese pasirinkti tinkamas pradines medžiagas bei kompleksus su metalais sudarančius reagentus: gadolinio jonų šaltiniu naudojant Gd2O3 buvo gauti geresni rezultatai nei naudojant Gd(NO3)3•6H2O, vienfazis GdAlO3 gali būti sėkmingai susintetintas kompleksus sudarančiu reagentu naudojant tiek natūralią vyno rūgštį, tiek 1,2 etandiolį, tiek citrinų rūgštį, tiek citrinų rūgšties ir etanolamino mišinį. Nustatyta, kad sintetinant stronciu pakeistus gadolinio aliuminatus Gd1–xSrxAlO3– (x = 0,10, 0,25, 0,50, 0,75), tinkamesnis gadolinio jonų šaltinis yra gadolinio oksidas nei gadolinio nitratas heksahidratas, kompleksus sudarantis reagentas – EDTA nei natūrali vyno rūgštis. Vienfazis perovskito struktūros stronciu pakeistas gadolinio aliuminatas Gd0,90Sr0,10AlO3– buvo susintetintas zolių-gelių metodu 1000 oC temperatūroje, gadolinio jonų šaltiniu naudojant Gd2O3, stroncio jonų šaltiniu – Sr(NO3)2, kompleksus sudarančiu reagentu – EDTA. Be to, 800 ºC iškaitinimo temperatūra yra per maža šiems junginiams sintetinti. Pirmą kartą pasiūlytas vandeninis zolių gelių metodas lantano ir gadolinio kobaltatams... [toliau žr. visą tekstą]In the present thesis the reported results let us to conclude that the developed aqueous sol–gel procedure could be successfully used for the low-temperature synthesis of monophasic perovskite gadolinium aluminate ceramics. It was also demonstrated that the selection of raw materials for the sol–gel processing should be done with care. Monophasic perovskite structure gadolinium aluminate GdAlO3 has been synthesized by sol gel synthesis method at 1000 oC, using gadolinium oxide as gadolinium raw material and 1.2 ethanediol, natural tartaric acid, citric acid or mixture of citric acid and ethanolamine as complexing agent. According to the XRD results, the Gd2O3 instead of Gd(NO3)36H2O preferably should be used as starting material for the preparation of GdAlO3. Monophasic perovskite structure strontium substituted gadolinium aluminate Gd0.90Sr0.10AlO3– was synthesized by the same sol gel synthesis method at 1000 oC, using gadolinium oxide as gadolinium raw material, strontium nitrate as strontium ion source and EDTA as complexing agent. It was proved that better gadolinium ion source is gadolinium oxide than gadolinium nitate hexahydrate, better complexing agent – EDTA than natural tartaric acid in the synthesis of GdAlO3 and strontium substituted Gd1–xSrxAlO3– (x = 0.10, 0.25, 0.50, 0.75) samples. According to the XRD results, increasing amount of strontium reduces amount of peaks of perovskite structure gadolinium aluminate. Besides, 800 ºC temperature is too low for the... [to full text]
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Husťák, Miroslav. "Vysoce porézní keramické oxidové materiály pro environmentální katalýzu." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-449796.
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As far as the replacement of fossil fuels with more environmentally friendly options is concerned, hydrogen is considered as the most promising source of energy. Currently, hydrogen is mainly produced through the method of methane reforming. This method requires the utilisation of catalysts made of precious metals. This master's degree thesis therefore investigates perovskite materials SmCoO3, Sm0,8Ca0,2CoO2,9, SmCo0,8Al0,2O3 and Sm0,8Ca0,2Co0,8Al0,2O2,9, which could be utilised as catalysts in the production of hydrogen by methane reforming. Methane reformation occurs on the surface of a catalyst. Therefore, it is desirable to ensure that the specific surface area of a catalyst material is as large as possible. For that reason, the aforementioned perovskite materials were prepared by two sol-gel methods, which are expected to create perovskites with large specific surface areas. It was investigated in the course of the work how the method of synthesis affects the structure and catalytic properties of individual materials. The SmCo0,8Al0,2O3 material prepared by a sol-gel synthesis with propylene oxide as a gelation agent demonstrated the best results - the measurement of catalytic activity showed that the methane conversion had achieved the value of 99%.
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Liu, Tianyu. "Perovskite Solar Cells fabrication and Azobenzene Perovskite synthesis: a study in understanding organic-inorganic hybrid lead halide perovskite." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1576840261464488.
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Baker, Sara Jane. "Oxygen diffusion in natural and synthetic perovskites." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287878.
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Tang, Yawei. "Synthesis and characterisation of iron-containing perovskites." Thesis, University of Oxford, 2018. http://ora.ox.ac.uk/objects/uuid:993996ed-92ee-4ddf-963d-d98eafc99580.
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In this research project, iron-containing perovskites with the general formulae A3Fe2B'O9, A2A'Fe2B'O9 and A2A'FeB'B''O9 have been synthesised using conventional solid-state reactions. A combination of experimental techniques has been applied to characterise the samples. The main aspects studied include their crystal symmetry, cation ordering pattern and magnetic behaviour. We have shown for the first time that Sr3Fe2TeO9 can adopt a trigonal perovskite-like structure with the Fe3+ and Te6+ cations ordering in a 2:1 sequence. However, the trigonal structure is disrupted by both nanotwinning and regions where the cations order in a 1:1 sequence. These disruptions prevent full antiferromagnetic ordering throughout the sample and the unordered spins form a spin-glass phase that coexists below 80 K. The identification of this disorder has allowed us to account for inconsistencies in the existing literature. Ba3Fe2TeO9 is a 6H perovskite in which the cation sites in the face-sharing octahedra and the vertex-sharing octahedra are occupied by different fractions of Fe3+. At a temperature close to 300 K the atomic moments begin to order in an antiferromagnetic manner, and the spins that are unable to take part in the long-range magnetic order form clusters that freeze at 18 K. In the series SrxBa3-xFe2TeO9 (x=1~2.5), as x decreases the crystal structure switches from purely pseudo-cubic to purely hexagonal via a biphasic region, illustrating the effect of the radius ratio rA/rB on crystal structure. A2LaFe2SbO9 (A=Ba, Sr, Ca) and CaLa2Fe2SnO9 have cation disorder on their A sites. Ca2LaFe2SbO9 and CaLa2Fe2SnO9 both adopt a monoclinic P21/n structure and Sr2LaFe2SbO9 adopts a triclinic P -1 structure, all of which show different levels of B-cation ordering. Ba2LaFe2SbO9 has a Pbnm structure with disordered B sites. These perovskites are not paramagnetic at 300 K, and they all adopt a G-type magnetic structure, which leads to long-range ferrimagnetic or weak ferromagnetic behaviour. The three antimonycontaining compounds contain a minor spin-glass-like phase below 50 K, while CaLa2Fe2SnO9 has a relatively well-developed magnetic backbone at 300 K. We found that the six-coordinate cations in the P21/n perovskite SrLa2FeCoSbO9 order in a previously unreported manner. The observed cation distribution, with diamagnetic Sb5+ and magnetic Co2+ each partially occupying only one of the six-coordinate sites, results in ferrimagnetism below the Curie temperature of 215 K. CaLa2FeCoSbO9 and ALa2FeNiSbO9 (A=Ba, Sr, Ca) were prepared as analogues of SrLa2FeCoSbO9, and they have similar crystal structure and high Curie temperatures. However, TEM revealed the different levels of inhomogeneity present in these four compounds. The inhomogeneity is least significant in CaLa2FeCoSbO9, and it is most significant in BaLa2FeNiSbO9 where both primitive phase and body-centred phases have been observed in a single crystallite. Consequently, doubt has been cast on the interpretation of the diffraction data for these inhomogeneous samples. A2LaFe2NbO9 (A=Sr, Ca) and CaLa2Fe2TaO9 were prepared with d0 cations for comparison with the perovskites containing d10 B-cations. Ca2LaFe2NbO9 and CaLa2Fe2TaO9 adopt the P21/n structure, and Sr2LaFe2NbO9 adopts the P -1 structure. These three perovskites show less well-developed ordering pattern than their antimony analogues due to the smaller difference in size of B-cations. They are not simple paramagnets at 300 K, and they all adopt a G-type magnetic structure with long-range ferrimagnetism. However, the formation of magnetic backbone is significantly slowed down from that in the d10 compounds and the temperature for the paramagnetic spins to freeze is lowered below 20 K. We propose that in these materials a J3 interaction occurs via the Fe3+ - O - Nb5+/Ta5+ - O - Fe3+ pathway to compete with the dominant J1 interaction. The J3 interaction is more significant when d0 cations are present because hybridisation of the empty d orbitals and the anion p orbitals facilitates virtual electron transfer.
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Frampton, Philip. "Synthesis and characterization of perovskite-related materials." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426404.
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Wallace, Thomas Kerr. "The synthesis and characterisation of novel molybdenum double perovskites." Thesis, University of Aberdeen, 2014. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=225337.
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Interest in the molybdenum double perovskites has increased since the discovery of high temperature, low field magnetresistance in Sr2FeMoO6. Molybdenum double perovskites of the form Ba2LnMoO6 (where Ln = Sm, Sm0.5Eu0.5, Eu, Gd, Pr) as well as Sr2ScMoO6 have been synthesized by solid-state reactions up to 1200°C. Laboratory X-ray diffraction, variable temperature neutron and synchrotron X-ray diffraction as well as DC-SQUID magnetometry have been employed, in order to investigate the intricate relationship between spin, lattice and orbital degrees of freedom within these compounds. A variable temperature neutron diffraction experiment has been performed on the molybdenum double perovskite Ba2154SmMoO6 between 353 and 877 K in order to further investigate the crystal structure into the high temperature regime. Variable temperature neutron diffraction studies of Ba2PrMoO6 have been performed to investigate the links between structure, spin and orbital order in this material. A synchrotron X-ray diffraction study of Ba2GdMoO6 is detailed. Ba2GdMoO6 exhibits a ferroelastic phase transition below 220 K; the first time this has been reported in a Mo5+ double perovskite. Furthermore, a study of the geometrically frustrated double perovskite Sr2ScMoO6 has been carried out, in order to further investigate the exotic new valence bond glass phase. The results shed new light on the complex relationship between spin, lattice and orbital degrees of freedom in Ba2LnMoO6 double perovskites.
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Moore, Caroline A. "Synthesis and characterisation of low-dimensional oxides." Thesis, University of Oxford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289407.
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Gurusinghe, Nicola Narmada Muthumanike. "Synthesis and characterisation of some layered and perovskite." Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4052/.
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The perovskites LaSr₂Fe₂SbO₉ and La₂Sr₂Fe₃SbO₁₂ crystallise in P2₁/n space group with Fe³⁺ occupying the two crystallographically distinct six-coordinate sites in a ratio of approximately 1:2. Neutron diffraction data suggest a G-type long-range antiferromagnetism in both materials at 2 K and 300 K. The A site cation ordering in Ln₂SrFe₂O₇ (Ln = La, Nd, Eu) and La₂BaFe₂O₇ increases as the mismatch in A site cation size increases. These phases exhibit long-range antiferromagnetic ordering at 300 K and 2 K; the magnetic moments in La₂BaFe₂O₇ and Nd₂SrFe₂O₇ gradually rotate in the temperature ranges 210 K to 190 K and 17 K to 9 K, respectively. The fluorine incorporation into these phases happens via anion insertion and anion substitution. The partial cation ordering or large overall size of the A site cations allows accommodation of more F⁻ ions causing no change to the Fe oxidation state. Both CaMnO₃₋δ and SrFeO₃₋δ are amenable to phosphate and sulphate anion incorporation. The unit cell sizes increase with the increase of dopant level. The oxy-anion insertion stabilises the cubic structure in all doped phases of SrFeO₃₋δ, but only the higher phosphate levels of CaMnO₃₋δ phases. The anion incorporation induced some mixed ion valencies but failed to introduce extra oxygen vacancies.
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McCabe, E. E. "Synthesis and characterisation of layered, perovskite-related materials." Thesis, Birmingham City University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.539316.
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Hoang, Minh Tam. "Metal halide perovskite nanocrystals: From synthesis to applications." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/227764/1/Minh%20Tam_Hoang_Thesis.pdf.
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This thesis primarily focuses on perovskite nanocrystals (NCs), addressing synthesis of the materials with tailored optical and electrical properties, morphology, stability for applications in optoelectrical devices and catalytic reactions. In particular, the methods of solvent engineering and compositional engineering were applied to tackle the toxicity and stability issues of the metal halide perovskite NCs. Advanced measurements were used to investigate the fundamental properties of the metal halide perovskite NCs. The developed perovskite NCs were successfully employed in highly efficient light emitting devices and catalytic applications.
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Nascimento, Cássia Costa. "Síntese de cerâmicas tipo perovskita com potencial uso em células solares." Universidade Federal de São Carlos, 2017. https://repositorio.ufscar.br/handle/ufscar/8819.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Visible light accounts for the biggest fraction of the solar irradiance. One of the strategies for achieving higher photovoltaic power conversion efficiency is the application of low band-gap materials (Eg ideal≈1.4 eV) capable of absorbing this fraction of the solar spectrum. Ferroelectric semiconductors have been studied in this field due to the above-bandgap generated photovoltages and their ferroelectric polarization-driven carrier separation. Ferroelectric oxides usually present wide bandgaps which allow the absorption of only 8-20% of the solar spectrum. However, the development of new ferroelectric materials, particularly KBNNO [KNbO3]0,9[BaNi0,5Nb0,5O3-δ ]0,1 (Eg = 1.39 eV) and KBiFe2O5 (Eg=1,60 eV), has encouraged the use of such materials in solar cells. Simple synthesis routes, with short steps, time and temperatures are essential for the future progress of the application of such ferroelectric oxides in solar cells. KBNNO and KBiFe2O5 require high crystallization temperatures, which reduce the number of potential substrates and electrode materials that could be used in devices, as polymer-based flexible ones. Obtaining this oxides in a high surface-area powder form might be a strategy to further incorporation in solar cells composed of low-temperature processing materials. This work reports for the first time synthesis of KBNNO and KBiFe2O5 by solution combustion (SCS). Characterization by WAXD, SEM, EDS, TG/DSC and Diffuse Reflectance UV-Vis Spectroscopy and dielectric constants indicates the success of the synthesis. The optical properties show the visible-light absorption contribution and band-gaps closer to the ideal magnitude for solar applications compared to the non doped materials. The SCS was shown as an effective route to obtaining the phase. Furthermore, it is possible to improve it in order to produce powders with smaller particle size and absent of secondary phases.
A luz visível representa a fração mais relevante da radiação solar. Desta maneira, busca-se empregar nas camadas ativas das células solares materiais com baixos band-gaps (Eg ideal ≈1,4 eV), capazes de absorver fótons nessa região do espectro. Semicondutores ferroelétricos com estrutura da perovskita ou estruturas relacionadas têm sido estudados nesse campo devido ao potencial de obtenção de voltagens superiores à magnitude de seus band-gaps e à contribuição na separação de portadores de cargas decorrente da polarização intrínseca presente nesses materiais. Óxidos ferroelétricos geralmente possuem Eg elevados (2,7-4 eV), permitindo o aproveitamento de somente 8-20% do espectro solar. No entanto, o desenvolvimento de novos semicondutores ferroelétricos, particularmente a KBNNO [KNbO3]0,9[BaNi0,5Nb0,5O3-δ ]0,1 (Eg=1,39 eV) e KBiFe2O5 (Eg=1,60 eV), tem encorajado a aplicação desses materiais em células solares. Rotas de síntese simples, com etapas, tempos e temperaturas reduzidas são essenciais para o progresso futuro da aplicação de tais óxidos ferroelétricos em células solares. A KBNNO e KBiFe2O5 cristalizam em temperaturas mais elevadas do que perovskitas orgânico-inorgânicas, o que reduz a possibilidade de fabricação de dispositivos na presença de substratos e eletrodos sensíveis à temperatura, como substratos poliméricos flexíveis. Assim, a obtenção desses óxidos na forma de pós de elevada área superficial pode ser uma estratégia para posterior incorporação em dispositivos contendo materiais processados a baixas temperaturas. Neste trabalho, reporta-se pela primeira vez a síntese da KBNNO e KBiFe2O5 por combustão em solução. Caracterizações por DRX, MEV, EDS, TG/DSC, Espectroscopia UV-Vis e constantes dielétricas indicam a obtenção das fases com sucesso. As propriedades ópticas confirmam contribuição na absorção da luz visível com respeito aos materiais não dopados, KNbO3 e BiFeO3. A síntese por combustão em solução se mostra efetiva para obtenção das fases, mas passível de melhorias para produção de pós com menor tamanho de partícula e sem a presença de fases secundárias.
CNPq: 155305/2014-0
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Lufaso, Michael Wayne. "Perovskite Synthesis and Analysis Using Structure Prediction Diagnostic Software." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1039132858.
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Bartoníčková, Eva. "Syntéza a analýza kompozitních oxidových keramik v přítomnosti nekonvenčních energetických polí." Doctoral thesis, Vysoké učení technické v Brně. Fakulta chemická, 2010. http://www.nusl.cz/ntk/nusl-233312.
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Synthesis and bulk analysis of composite ceramic oxide materials and materials with perovskite-defect structure is presented within this work. Syntheses of these advanced ceramics materials were carroed out by using of nonconventional techniques (microwave-assisted hydrothermal synthesis and polycondensation techniques) and by conventional mechanochemical activation followed by high temperature solid state reaction. X-Ray difraction (XRD), Rietveld analysis, scaning microscopy (SEM), microalysis EDS-SEM, thermal analysis (TG), infrared spectroscopy (IR), determination of particles size and specific surface area were used for description of synthesized products. In case of perovskite system based on La-Sr-Fe-Ti-O electrochemical properties were studied. Part of work was focused on chemical analysis of synthesized composite oxide materials and decomposition hard structured products by using of nonconventional fields.
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McClure, Eric Thomas. "Synthesis and Characterization of New Visible Light Absorbing, Lead-Free Halide Double Perovskite Semiconductors." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492431322941272.
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Chakravorty, Ruma 1973. "Synthesis and sintering of nanostructured multicomponent perovskites." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/9866.
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Sher, Falak. "Synthesis and properties of magnetoresistive double perovskites." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614834.
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Guggilla, Srinivas. "Synthesis and characterization of Perovskite-related ionic and mixed ionic-electronic conductors /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Akizuki, Yasuhide. "High-Pressure Synthesis and Properties of Novel Perovskite Oxides." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199319.
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Kususe, Yoshiro. "Synthesis, Structure, and Properties of Eu2+-containing Perovskite Oxides." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199320.
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Bos, J. W. G. "Synthesis, structures and properties of new double perovskite oxides." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596791.
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Double perovskite oxides have attracted much interest since the discovery of spin-polarized conduction and large low field magnetoresistances in Sr2FeMoO6. This behaviour exists to high temperatures, making Sr2FeMoO6 and related materials candidates for application in data storage devices. This thesis describes the synthesis, structures and properties of some new double perovskite oxides. These can be divided into the (LaM)BNbO6 (M = Ca, Sr, Ba; B = Mn, Co) and LaSrFeNbO6 materials that have one magnetic transition metal (TM) cation, and the (La1+xM1-x)CoRuO6 (M = Ca, Sr; -0.25 £ x £ 0.25 x = 1) materials that have two magnetic TM cations. The (LaM)CoNbO6 double perovskites crystalize with the monoclinic P21/2 (M = Ca, Sr) and tetragonal 14/m (M = Ba) superstructures, which have rocksalt ordered arrangements of Co2+ (3d7) and Nb5+ (4d0), with almost no Co/Nb inversion (<4%). All three phases are anti-ferromagnetic with Neel temperatures of 17 K (M = Ca), 16 K (M = Sr) and 10K (M = Ba). The magnetic ordering is described by the magnetic propagation vector k = ( ½ 0 ½ ) for all materials. For M = Ca and Sr, two “non-collinear” and two “collinear” magnetic structures are found. These are experimentally indeterminate because of the small monoclinic angle (b = 89.90). The M = Ba material has a collinear antiparallel magnetic structure. The saturated cobalt moment decreases from 2.97(2) mB to 2.52 (3) mB to 1.85 (5) mB for M = Ca, Sr and Ba, respectively. The frustration due to competing 900 exchange interactions. The (LaK)MnNbO6 materials also have the monoclinic P21/n (M = Ca, Sr) and tetragonal 14/m (M = Ba) superstructures, with <3% inversion of Mn2+ (3d5) and Nb5+ (4d0). All materials are antiferromagnetic with Neel temperatures of 9 K (M = Ca), 8 K (M = Ba) and 6.5 K (M = Ba). The magnetic Bragg reflections are indexed by k = (0 ½ ½ ), and the possible magnetic models are identical to those for (LaM)CoNbO6. The manganese saturation moment decreases from 4.77(3) mB (M = Ca) to 4.43 (4) mB (M = Sr) to 41.9 (4) mB (M = Ba). (LaSr)FeNbO6 has the monoclinic P21/n superstructure with 14% inversion of Fe2+ (3d6) and Nb5+ (4d0). This material is antiferromagnetic (TN = 22 K), and has a ( ½ 0 ½) magnetic propagation vector (mFe = 3.45(3) mB). The lattice parameters, antisite disorder, Neel temperatures and resistivities of the (La1-xM1-x)CoRuO6 double perovskites are found to vary in a systematic manner. The Co/Ru antisite disorder is minimal for x = 0, showing that this disorder is driven by the mixed Co or Ru electronic states at x ≠ 0 rather than by La/M cation mixing. The x = 0 materials have TN = 96K (M = Ca) and TN = 85 K (M = Sr), and are variable range hopping semiconductors. Hole doping )x < 0) results in a rapid reduction in the resistivity while the Neel temperature increases only moderately, whereas electron doping (x > 0) results in a significant reduction in TN but has little effect on the resistivity. X-ray absorption near edge spectroscopy shows that for x < 0, the Co2+ states are selectively hope doped while for x > 0 only the Ru5+ states are electron doped, which is in keeping with the strongly asymmetric doping response.
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El-Shinawi, Hany Zakaria Ibrahim. "Synthesis and characterization of cobalt-containing perovskite-type oxides." Thesis, University of Birmingham, 2010. http://etheses.bham.ac.uk//id/eprint/625/.
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A number of cobalt-containing perovskite-type oxides were synthesized and characterized in this study. All materials were half-doped with cobalt in their B-sites, i.e. contain the Co0.5M0.5 B-site state where M = Fe, Mn, Cr, Ni; the materials adopted single layered, double-layered and simple perovskite-type structures. The materials La2 xSrxCo0.5M0.5O4 (M = Fe, Cr) have shown enhanced stability under reducing conditions (10% H2/N2, up to 1000 ºC) with the formation of oxygen deficient compounds, while no evidence for oxygen hyperstoichiometry was observed under oxidizing conditions. Materials such La1.2Sr0.8Co0.5Mn0.5O4.1 and La1.7Sr0.3Co0.5Ni0.5O4.08, however, exhibit oxygen hyperstoichiometry under oxidizing conditions and also withstand reducing conditions via formation of oxygen deficiency. Oxygen vacancies were disordered and confined to the equatorial planes of the single layered structure in all materials, while oxygen hyperstoichiometry was accommodated in the interstitial (0, 0 .5, 0.25) sites of the tetragonal structure. In La1+xSr2 xCoMnO7-δ, oxygen vacancies were confined to the common apex of the double layered structure. The new brownmillerite phase LaSrCoFeO5 was synthesized and fluorination produced the new oxyfluoride LaSrCoFeO5F. Magnetic interactions between Co2+(3+) ions and ions such as Fe3+, Mn3+, Cr3+, Ni2+ in different perovskite-type structures were also studied and a range of magnetically ordered materials, at low and room temperatures, were investigated.
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Rogers, Fiona Kate. "Combinatorial synthesis and high throughput screening of Perovskite Electrocatalysts." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/409725/.
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Compositionally graduated films of a SrTi1-xFexO3-y (STFO) perovskite electrocatalyst were successfully prepared by High Throughput Physical Vapour Deposition (HT-PVD). X-ray diffraction measurements confirmed a cubic perovskite structure for all values of x as well as an increase in the cubic lattice parameter with increasing x from 0.392 ± 0.001 nm for SrTiO3 to 0.386 ± 0.001 nm for SrFeO3 in accordance with Vegard’s Law. A Raman mode corresponding to an O-stretching vibration was observed which is disallowed by symmetry in the cubic structure and suggests a localised lattice distortion. The films were highly resistive, < 7 x 10-8 S cm-1, at low x but conductivity increased with increasing x before reaching a plateau at 0.041 S cm-1 for x > 0.75.High electrocatalytic activity towards the oxygen evolution reaction (OER), characterised by over-potentials below 0.2 V, was found for STFO electrode compositions with x > 0.5. The high OER activity was however found to correlate with low electrode stability, consistent with the participation of lattice oxygen in the OER mechanism. This was supported by the observed redox electrochemistry which showed evidence of reversible oxygen intercalation. An optimal electrode composition of SrTi0.5Fe0.5O3-y is recommended as OER activity showed no significant increase for higher Fe content whilst electrode stability decreases. Low electrocatalytic activity towards the oxygen reduction reaction (ORR) was observed for all compositions. The ORR did not occur until after surface reduction of the films suggesting that the surface reduction is required for the creation of active surface sites. The STFO perovskite system was also investigated on Fe doped STO (110) surfaces. A series of reconstructed surfaces were prepared and characterised by low energy electron diffraction (LEED) in agreement with the literature. X-ray photo-electron spectroscopy (XPS) and low energy ion scattering spectroscopy (LEISS) confirmed that Fe doping was successful in incorporation of Fe into the perovskite structure. Fe incorporation was observed to improve the ORR electrocatalytic activity of the surface however no OER electrocatalytic activity was observed.
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Porter, Spencer H. "Perovskite and Pyrochlore Tantalum Oxide Nitrides: Synthesis and Characterization." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1332499280.
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Greul, Enrico [Verfasser], and Thomas [Akademischer Betreuer] Bein. "On the way to non-toxic and highly stable perovskite-based optoelectronics : synthesis and investigations of lead-free perovskites for photovoltaic applications / Enrico Greul ; Betreuer: Thomas Bein." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/119109815X/34.
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Tang, Ya. "Studies on perovskite oxyhydrides: catalysis and hydride anion diffusion." Kyoto University, 2018. http://hdl.handle.net/2433/232484.
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Chavez-Carvayar, Jose Alvaro. "Synthesis and characterisation of new calcium-ferrite based phases." Thesis, University of Aberdeen, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318281.
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Phase formation studies in the quaternary section Ca2-ySryFe2-xB'xOγ : B' = Nb, Ta, 0 ≤ y ≤ 2.0 and 0 ≤ x ≤ 2.0 were carried out. Results are summarised below for B' = Nb; for B' = Ta they were broadly similar. Four solid solution phases were found: i) a cubic solid solution, with a variable compositional extent x, which increased with substitution of Ca by Sr, from 0.45 ≤ x ≤ 0.65 for y = 0, to 0 ≤ x ≤ 1.2 for y = 2.0. ii) A limited orthorhombic solid solution along the Ca2Fe2O5-Ca2B'2O7 join with 0.8 ≤ x ≤ 1.0. iii) A complete range of orthorhombic, brownmillerite solid solution for x = 0 and iv) an orthorhomic, perovskite-related solid solution, isostructural with Ca2Nb2O7, for x = 2.0. A combination of differential thermal analysis, thermogravimetry, Mössbauer spectroscopy, high temperature powder X-ray diffraction, Rietveld refinement, a.c. impedance spectroscopy and magnetic susceptometry has been used to characterise these new phases. Solid solution (i) has variable oxygen content with an oxygen-deficient perovskite structure. As synthesised, for x = 0.6 it contains a mixture of Fe4+ and Fe3+ in the ratio 13/87. The oxygen content could be modified by heat treatment under various atmospheres over the range 5.5. ≤ γ ≤ 5.92 which corresponded to the ratios: 93/7 to Fe3+/Fe2+ and 42/58 of Fe4+/Fe3+. At higher oxygen contents, γ > 5.7, transformation to an orthorhombic structure was observed. The electrical resistivity was dominated by grain boundary effects. Conduction is electronic and is attributed to hopping between iron in mixed oxidation states. The resistivity increased dramatically on reduction and became n-type, presumably due to a small fraction of Fe2+ present.
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Tseggai, Mehreteab. "Synthesis, Nuclear Structure, and Magnetic Properties of some Perovskite Oxides." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4826.
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SHAMSI, JAVAD. "Colloidal Synthesis of Lead Halide Perovskite Nanocrystals for Optoelectronic Application." Doctoral thesis, Università degli studi di Genova, 2018. http://hdl.handle.net/11567/929994.
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Adkin, Josephine J. "The synthesis and characterisation of some hexagonal perovskites." Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:9b339008-23e6-432f-ad59-b90a018c9740.
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The structural chemistry and magnetic properties of a number of manganese containing hexagonal perovskites have been studied by X-ray diffraction, neutron diffraction and magnetometry. Trends in the magnetic properties are investigated as a function of the hexagonal stacking sequence and manganese oxidation state. The synthesis of the series of BaMnO3-x hexagonal perovskites is discussed. By varying both the partial pressure of oxygen and the firing temperature, stacking sequences with a range of hexagonal to cubic layer ratios can be synthesised. Factors which increase the structural tolerance factor are found to increase the proportion of hexagonal layers in the stacking sequence. The crystallographic properties of the BaMnO3-x compounds are discussed, and the oxide vacancies are found to be exclusively located in the face-sharing hexagonal (h) layers, particularly those which are adjacent to two apex-sharing cubic (c) layers. The preferential localisation of oxide vacancies in chc sites can be used to rationalise the observed stacking sequences, as well as the limiting stoichiometries of BaMnO3-x structures. The magnetic behaviour of the BaMnO3-x phases is investigated, both individually and as a function of the stacking sequence. A strong direct exchange interaction between face-sharing cations couples all magnetic moments antiferromagnetically above ambient temperature. A slightly weaker interaction (utilising the 180° superexchange pathways between apex-sharing MnOe octahedra) results in three-dimensional antiferromagnetic order at a temperature in the range 230 ≤ T (K) ≤ 280. The strength of this interaction is found to be dependent on the length of the face-sharing chains. A third interaction occurs at T ~ 45K, believed to represent a canting transition. Low temperature neutron diffraction data reveal that the magnetic moments order in a simple antiferromagnetic manner. The magnitude of the ordered moment shows a dependence on the length of the face sharing chains, where phases with shorter chains have a larger ordered moment. Long-range magnetic order is disrupted by charge disorder in the mixed Mn(III)/Mn(IV) system 4H-BaMnO2.6 5(1). The hexagonal BaMn1-zTiz O3- x and BaMn1-zZrz03-x systems were also studied. Synthesis under argon atmospheres allows a range of new phases to be accessed. These include a novel manganese-zirconium phase, 6H-BaMn0.8Zr0.2O2.81(1), and BaMno.55Ti0.45,/sub>O3-x, which adopts the rare 15R' stacking sequence. The BaMn1-z TizO3-x system confirms that although the tolerance factor controls the proportion of cubic layers, it does not control the arrangement of these layers. This is controlled by the size of the B cations and the proportion of oxide vacancies. Partial cation order occurs in 6H-BaMno.8Zr0.2O2.81(1), which can be rationalised on the basis of the size difference between manganese and zirconium ions. Topotactic reductions using binary hydrides are carried out in order to decouple the manganese oxidation state from the adopted stacking sequence. Using hydride reductions, 4H-Bao.5Sro.5MnO3-x can be topotactically reduced to 4H-Bao.5Sro.5MnO2.o2(1). This increases the strength of the 180° superexchange interaction, and antiferromagnetic order is achieved above ambient temperature. Using the same techniques, 4H-BaMnO3-x can be reduced to 4H-BaMnO2.47(1) or 4H-BaMnO2.o6(1). These phases undergo a distortion to an orthorhombic unit cell.
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Gustin, Lea. "Synthesis and Topochemical Manipulation of New Layered Perovskites." ScholarWorks@UNO, 2016. http://scholarworks.uno.edu/td/2149.
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Metastable layered perovskites containing interlayer transition metals can readily be obtained by simple ion exchange reactions on receptive hosts, such as those of the Dion-Jacobson and Ruddlesden-Popper structure types. In this work, we focused on adding to the library of layered perovskites by not only creating new compounds, but by also showing their ability to be further manipulated, and by studying the stability of the series through thermal behavior studies.
The reactions with transition metal halides are particularly interesting since they often lead to novel architectures and magnetic behavior. On subsequent heat treatment, these exchange products typically decompose to thermodynamically more stable phases. The newly synthesized spin glass-like material, FeLa2Ti3O10, obtained by ion exchange of Li2La2Ti3O10 with FeCl2 at 350 °C, behaves differently. When heated to 700 °C, the compound undergoes a significant cell contraction (Δc ≈ -2.7 Å) with an increase in the oxidation state of iron present in the interlayer that not been observed before in such compounds. Efforts were also made to synthesize new series of compounds, here MSrTa2O7 (M= Co and Zn), with vacancies in the interlayer that could lead to future topochemical manipulations.
The ability to vary the composition of different phases to form solid-solutions through atomic substitution at the A or B sites with ions of similar or different charge can lead to new structures as well an enhancement of the properties of the original compound or new ones. The synthesis and characterization of the new mixed A-cation containing layered perovskite RbLaNaNb3O10, where La3+ and Na+ share the same site in the perovskite slab and RbLaCaNb2MnO10 that exhibits an ordering of the B site with Mn in the center of the perovskite slab will be presented. Further topochemical manipulation of these phases via ion exchange reactions at low temperatures (< 500 °C), lead to the new series A’LaNaNb3O10 and A’LaCaNb2MnO10 where A’= H, Li, Na, K and CuCl.
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Josepha, Elisha A. "Topochemical Manipulation of Layered Perovskites." ScholarWorks@UNO, 2011. http://scholarworks.uno.edu/td/464.
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Topochemical strategies, techniques that allow one to effectively manipulate the structures of nonmolecular solids once a crystal lattice is established, are effective in the low temperature (< 500 °C) modification of solid state structures, allowing the preparation of nonmolecular compounds not accessible by standard synthetic routes. Some of the techniques, ion exchange, intercalation/deintercalation, have proven to be excellent synthetic methods for preserving specific frameworks. The combination of these techniques can allow one to create a multistep approach that can be used to design new compounds with interesting properties.
As an expansion to the field of topotactic reactions, a multistep approach was developed towards the synthesis of the new compounds (A xM0.5Cly)LaNb2O7 (where A = Rb, Cs; M = Fe, Ni; x ≈ 1.5;y ≈ 1) at temperatures below 400oC. The first reaction step involved the ion exchange of the host materials (ALaNb2O7, A = Rb, Cs) to form the products M0.5LaNb2O7 (where M = Fe, Ni), a structure open to further chemistry. The next step involved reductive intercalation with Rb or Cs metal to form the air sensitive mixed-valence products with the nominal compositions, A1.5M0.5LaNb2O7. The last step involved the oxidative intercalation of chlorine using chlorine gas to obtain the final compounds. This multistep approach is a design to form mix-metal halide layers, specifically those with divalent cations, within layered perovskites, opening the doors to compounds that can have interesting properties.
This reaction series was also applied to the tantalate layered oxides, leading to the formation of the new compound Ni 0.5LaTa2O7 through ion exchange. The further multistep
topochemical manipulation of this new compound was not successful and was indicative of the difference in chemical behavior of the tantalates versus the niobates.
We have also investigated the oxidative intercalation of halogens into a series of Ruddlesden-Popper (R-P) ruthenate oxides with the formula Ae n+1RunO3n+1 (Ae = Ca, Sr; n = 1, 2, 3) using several sources of fluorine, chlorine, and bromine. A new method was developed to intercalate chlorine into layered systems; this new approach avoids the use of chlorine gas which is highly toxic. The new phase Sr3Ru2O7Cl0.7 was synthesized by the new method and further topotactic manipulations were explored. The chemistry was not limited to the n = 2 phase but was also applied to the n = 3 phase, Sr4Ru3O10.
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Gao, Weiran. "Synthesis and Quantification of Surface Reactivity on CsSnBr3 and Cs2TiBr6." Digital WPI, 2018. https://digitalcommons.wpi.edu/etd-theses/1322.
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We quantified the chemical species present at polycrystalline cesium tin bromide perovskite, CsSnBr3 and cesium titanium bromide antifluorite, Cs2TiBr6. For CsSnBr3, experiments utilized the orthogonal reactivity of the Cs+ cation, the Sn2+ cation, and the Br– halide anion. Ambient- pressure exposure to BF3 solutions probed the reactivity of interfacial bromines. Reactions with p-trifluoromethylanilinium chloride probed the exchange reactivity of the Cs+ cation. A complex-forming ligand, 4,4’-bis(trifluoromethyl)-2,2’-bipyridine, probed for interfacial Sn2+- site cations. For Cs2TiBr6, both BF3 and (C6F5)3B probed the reactivity of interfacial bromines. Fluorine features in x-ray photoelectron spectroscopy (XPS) quantified reaction outcomes for each solution-phase species. XPS indicated adsorption of BF3 on CsSnBr3 and (C6F5)3B on Cs2TiBr6 indicating surface-available halide anions on both surfaces. For CsSnBr3, temperature- programmed desorption (TPD) quantified a ~215 kJ mol–1 desorption energy of BF3 on the surface. Adsorption of the fluorinated anilinium cation included no concomitant adsorption of chlorine as revealed by the absence of Cl 2p features within the limits of XPS detection. The bipyridine ligand demonstrated adsorption to CsSnBr3. We discuss the present results in the context of interfacial stability, passivation, and reactivity for solar-energy conversion devices.
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BONOMI, SARA. "Perovskites for optoelectronic applications: new synthetic approaches and properties modulation routes." Doctoral thesis, Università degli studi di Pavia, 2022. http://hdl.handle.net/11571/1450823.
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The development and the increasing application of renewable sources are two pivotal points of the solutions set for the huge climatic challenge that all the world is facing nowadays. Apart from the classical silicon-based photovoltaic panels, one of the most flourishing fields is that of metal halide perovskites (MHPs). The enormous attractiveness of MHPs relies on their outstanding optoelectronic properties and their applicability in many different fields. Their extreme tunability is due to their structure, and consequently their properties' ease of modification. All MHPs are constituted by a network of octahedra: when they share 6, 4, 2, and 0 corners the structure is respectively called 3D, 2D, 1D, and 0D perovskite, with 3D being the most efficient. However, even though only limited amounts of Pb are implemented in solar cells, there is a potential risk of harm to humans and the environment. Therefore, researchers are currently trying to substitute Pb with other suitable elements to develop novel, low-cost, non-toxic, and environment-friendly perovskite materials, that could be possibly capable of various applications with superior performances and long-term stability. In almost all the devices, the perovskite is present in form of thin film, therefore in literature many different growing methods can be found, either solution or vapor-based. Solution based ones are the most applied, but even the optimized techniques are affected by many shortcomings, such as: a lack of control over the low-temperature crystallization process, which is affected by many factors and often leads to poor reproducibility in properties; the solvent employed in depositing a perovskite layer washes away the underlying ones, so the sequential film deposition and the deriving perovskite-perovskite heterostructures are very difficult to realize; the complex fluid dynamics during the scale-up of solution methods do not permit the growth of uniform thin films in panel-size substrates due to the many intermediate phases that coexist during the crystallization process; the common wet-chemistry protocols used for hybrid phases do not assure good results in totally inorganic perovskite deposition, mainly because of the poor solubility in polar solvents of many halide precursors. The main aims of this thesis are: the realization of new approaches to tune, in a stable way, the optical and structural properties of perovskites in order to extend their range of applications; the development of different environmental-friendly scale up methods suitable to prepare perovskite phases for optoelectronic devices and to stabilize metastable phases. For these purposes, we focused on industrial types of equipment and techniques that could fit our scopes. The first part of this work is about employing and optimizing a vapor-based technique to deposit metal halide perovskites thin films. The most employed physical vapor deposition method consists of different variations of thermal evaporation, therefore we decided to explore radio-frequency magnetron sputtering because of the advantages of simple equipment, easy control, large coating area, and strong adhesion. By means of this technique, a large number of thin films can be prepared at relatively high purity, high speed, low temperature, and low cost. The second section focuses on preliminary in-situ high-pressure studies of metal halide perovskites at large facilities. This investigation of MHPs is relatively recent and, while studies of temperature dependence modification and chemical tuning strategies exist, the knowledge of pressure-induced effects remains scarce. These studies could allow us to more precisely tune the properties through compression and also permit the discovery of new phases that subsequently could be stabilized at ambient conditions. The last part of this work is focused on the tuning of MHPs by the means of two industrial physical modulation techniques: spark plasma sintering and ball-milling.
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Chen, Chen. "Synthesis, structural and ferroelectric properties of perovskite-like layered structured materials." Thesis, Queen Mary, University of London, 2015. http://qmro.qmul.ac.uk/xmlui/handle/123456789/9526.
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Perovskite-like layered structured (PLS) compounds display a range of interesting physical and chemical properties, including photocatalysis, photoluminescence, ion conductivity, electrochemical stability, magnetic properties, ferroelectricity and piezoelectricity. There are mainly three homologous series of PLS compounds distinguished by their different BO6 octahedra orientation: the Dion-Jacobson phase (A'An-1BnO3n+1); the AnBnO3n+2 phase; and the hexagonal phase (AnBn-1O3n). Some of the 4-layer AnBnO3n+2 compounds, like La2Ti2O7 and Sr2Nb2O7, have been reported to be ferroelectrics with super high Curie point (above 1300 °C), but no ferroelectric properties have been reported for the 2-layer and 3-layer AnBnO3n+2 compounds, and also there are few reports on the ferroelectric properties of compounds with Dion-Jacobson structure and hexagonal structure. Consequently, in this work, the crystallographic structures, microstructures, dielectric, ferroelectric and piezoelectric properties of (AxLa1-x)Ti2O7 (A = Sm and Eu) solid solutions with 4-layer AnBnO3n+2 structure, Pr3Ti2TaO11 with 3-layer AnBnO3n+2 structure, LaTaO4 with 2-layer AnBnO3n+2 structure, ABiNb2O7 (A = Rb and Cs) with Dion-Jacobson structure and Sr6TiNb4O18 with hexagonal structure were studied. Spark plasma sintering (SPS) was used to sinter ceramics with high density and preferred orientation. X-ray diffraction refinement (XRD) and transmission electron microscopy (TEM) were used to study the crystallographic structures and microstructures of the layer structured compounds. The ferroelectricity was studied using the current-electric field and polarization-electric field hysteresis loops. The Curie point and phase transitions were studied using the temperature dependence of the dielectric constant and loss. Piezoresponse force microscopy (PFM) was also used to study the ferroelectric domain structure of some layer structured compounds. In the first part of this work, the piezoelectric constant of La2Ti2O7 was improved by doping Sm. The crystallographic structure of (Eu1-xLax) 2Ti2O7 and (Sm1-xLax) 2Ti2O7 solid solutions were well studied. (AxLa1-x)Ti2O7 solid solutions were isomorphous with La2Ti2O7 when x was less than 0.5 for (EuxLa1-x)Ti2O7 and 0.8 for (SmxLa1-x)Ti2O7. When x was above their solubility limit, a biphase was observed. The XRD and Raman data suggested that the biphase consisted of (AxLa1-x)2Ti2O7 perovskite-like layered structure and pure Sm2Ti2O7 pyrochlore structure. Ferroelectric domain switching was observed in the I-E and P-E hysteresis loops for textured (SmxLa1-x)Ti2O7 (x < 0.2). The highest d33 was 2.8 pC/N for (Sm0.1La0.9)Ti2O7. In the second part, The Pr3Ti2TaO11 compound was demonstrated to have a 3-layer type II AnBnO3n+2 PLS structure belonging to space group Pmc21 with unit cell parameters a = 3.8689(3) Å, b = 20.389(2) Å, c = 5.5046(5) Å, and its ferroelectric properties were investigated. Analysis of the XRD and TEM results showed that Pr3Ti2TaO11 ceramics have an n = 3 (type II) heteroblock structure consisting of alternating n = 2 and n = 4 octahedral oxide layers. High resolution electron microscopy revealed the layered structure to be highly disordered, with faulting of the heteroblock structure and the coexistence of a n = 4 phase on a fine scale (nm), which was evident as a broadening of the XRD peaks of the ceramics. Pr3Ti2TaO11 ceramic exhibits a super-high Curie point (1415±5 °C). A small, but measurable piezoelectric constant d33 between 0.1 and 0.2 pC/N was detected for the samples poled above 900 °C under an electric field of 100~200 V/cm. Pure LaTaO4 powders with orthorhombic phase were be prepared by co-precipitation method. The orthorhombic LaTaO4 powders have a 2-layer perovskite-like layered structure with space group A21am, which was refined using Rietveld method. The single phase O-LaTaO4 ceramic was prepared using SPS with a slow cooling rate (20 °C/min). A d33 of 0.3 pC/N was obtained from the electric field induced orthorhombic phase. In the second part of this work, the ferroelectricity and piezoelectricity of CsBiNb2O7 with Dion-Jacobson type PLS structure was successfully demonstrated for the first time. The ferroelectricity and piezoelectricity of RbBiNb2O7, which have similar structure with CsBiNb2O7, were also fully studied. Highly textured 2-layer Dion-Jacobson ceramics ABiNb2O7 (A = Rb and Cs) were prepared by one-step SPS. High resolution TEM showed well ordered (0 0 1) lattice planes. Striped ferroelectric domains were observed using PFM. The ferroelectricity and piezoelectricity of CsBiNb2O7 has been demonstrated for the first time. The Tc of RbBiNb2O7 and CsBiNb2O7 are 1098±5 and 1033±5 °C, respectively. The piezoelectric constant of RbBiNb2O7 and CsBiNb2O7 were approximately 5 and 8 pC/N. Thermal depoling studies confirmed the Curie point and the stability of the piezoelectricity. Sr6Nb4TiO18 ceramics with non-centrosymmetric structure were successfully prepared, but no obvious evidence was found to prove its ferroelectricity. The untextured and textured 6-layer Hexagonal compound Sr6Nb4TiO18 was prepared by solid state reaction and spark plasma sintering. Its Curie point was found to be greater than 1500 °C. No ferroelectric properties were observed by studying of I-E and P-E loops, and no d33 was observed after poling.
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Ren, Xiaolin. "Synthesis and characterisation of metal oxides and fluorinated perovskite-related oxides." Thesis, Open University, 2005. http://oro.open.ac.uk/54200/.
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Perovskite-related materials of composition LaFe1-xCoxO3 prepared by conventional calcination methods and mechanical milling are shown by temperature programmed reduction to be more susceptible to reduction in a flowing mixture of hydrogen and nitrogen by the incorporation of cobalt. X-ray powder diffraction and Mossbauer spectroscopy show that in iron-rich systems the limited reduction of iron and cobalt leads to the segregation of discrete metallic phases without destruction of the perovskite structure. In cobalt-rich systems, the reduction of Co3+ to Coo precedes complete reduction of Fe3+ and the segregation of alloy and metal phases is accompanied by destruction of the perovskite structure. Phases made by milling techniques were of smaller particle size and are more susceptible to hydrogen reduction than their counterparts made by conventional techniques. Materials of the type La0.5Sr0.5MO3 (M= Fe, Co) made by calcination methods are more susceptible to reduction when the transition metal M is cobalt as compared to iron. Perovskite-related oxides of composition La1-xSrxFe1-yCoyO3 have been fluorinated by reaction with poly(vinylidene fluoride). The materials have been characterised by X-ray powder diffraction and Mossbauer spectroscopy. Fluorination induces a reduction in the oxidation state of iron from Fe4+ to Fe3+. The fluorinated materials were magnetically ordered at 298 K. Compounds of the type SrFe1-xSnxO3 were found to contain Fe5+ and Fe3+. Fluorination resulted in reduction of the transition metal to Fe3+ and, in iron-rich systems, magnetic order. The compound Ba2SnO4 which adopts the K2NiF4-type structure has also been fluorinated by reaction with zinc fluoride. X-ray powder diffraction shows an enlargement of the unit cell of the fluorinated phase along the c-axis. Small particle iron- and vanadium- antimonate have been prepared by mechanical milling methods. The phases have been examined by M6ssbauer spectroscopy and can be formulated M3+Sb5+O4 (M = Fe, V). Thermal analysis suggests that the vanadium animonate formed by milling V2O5 and Sb2O3 in an inert atmosphere may be oxygen deficient. X-ray powder diffraction shows that milling also induces the phase transformation of the cubic senarmontite Sb2O3 form to the orthorhombic valentinite Sb2O3 form and of a-Sb2O4 to B-Sb2O4.
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Chen, Wei-tin. "Synthesis, structural and property studies of bismuth containing perovskites." Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/3861.
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Several bismuth-containing transition metal perovskites that are of interest as potential multiferroic materials have been synthesised and studied. These materials have been structurally characterised and their physical properties have been examined at varying temperatures and pressures. The new series of substituted bismuth ferrite perovskites BixCa1-xFeO3, where x = 0.4 - 1.0, has been prepared. A disordered cubic phase (x = 0.4 - 0.67) and the coexistence of rhombohedral and cubic phases (x = 0.8 and 0.9) have been observed. The x = 0.8 sample is located at the phase boundary and shows a transformation from cubic to rhombohedral symmetry at 473 - 573 K. All samples are antiferromagnets at room temperature and have Néel temperature of 623 - 643 K. Ferroelectric order is suppressed in the disordered cubic phase. BixLa1-xMnO3 materials with x = 0.8, 0.9 and 1.0 were synthesised at 3 - 6 GPa. For x = 1.0 and 0.9 samples a highly distorted perovskite structure with monoclinic space group C2/c was adopted and ferromagnetic behaviour was observed with Curie temperatures of 101 and 94 K, respectively. Bi0.8La0.2MnO3 shows an O'-type orthorhombic Pnma structure and canted A-type antiferromagnetic ordering below 80 K. A new phase of BiNiO3 has been discovered at 4 - 5 GPa below 200 K, in which a Pb11 symmetry has been revealed with a = 5.2515(2) Å, b = 5.6012(3) Å, c = 7.6202(4) Å and β = 90.20(1) º at 4.3 GPa and 100 K. This new Phase Id is derived from the ambient Phase I Bi3+ 0.5Bi5+ 0.5Ni2+O3, where the charge disproportionated Bi3+/Bi5+ cations become disordered. The updated P-T phase diagram of BiNiO3 is presented. BiCu3Mn4O12 has been studied by neutron diffraction from 5 to 400 K. The incorporation of Mn3+ into the Cu site has been observed, showing that the true composition is BiCu2.5Mn4.5O12. The ordering of Mn and Cu moments below transition temperature 320 K is found to be ferromagnetic rather than ferrimagnetic as proposed previously.
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Rawal, Ritesh. "Synthesis and characterisation of B-site deficient hexagonal perovskites." Thesis, University of Sheffield, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445124.
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Navas, Pérez Carlos Justo 1971. "Synthesis, electrical conductivity and nonstoichiometry of dopped layered perovskites." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/85242.
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Williams, Anthony James. "Synthesis and neutron diffraction studies of manganese oxide perovskites." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615786.
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Manjon, Sanz Alicia. "Synthesis, structure and properties of bismuth based electroceramic perovskites." Thesis, University of Liverpool, 2015. http://livrepository.liverpool.ac.uk/2011763/.
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The work presented in this thesis focuses on the effect on structure and properties of the rhombohedral (R) perovskite system, Bi(Ti3/8Fe2/8Mg3/8)O3 (BTFM), when solid solutions with CaTiO3 (CTO) are made. Bismuth-based perovskites are established as candidates to replace the piezoelectric material Pb(Zr1-xTix)O3 as they have high Curie and depolarisation temperatures which are necessary for applications and are not toxic. BTFM has a Curie temperature of ~730 °C; however it shows poor electromechanical properties. In Chapter 3 of this thesis is shown that a range of xBTFM-(1-x)CTO compositions were synthesised successfully in the range 0.6 ≤ x ≤ 1 obtaining the perovskite structure. They were proved to be polar by second harmonic generation measurements. Compositions in the range 0.6 ≤ x ≤ 0.825 adopt an orthorhombic (O) structure. For x ≥ 0.95 the R structure crystallises in the polar space group R3c with polarisation along [111]p as BTFM while in the range 0.837 ≤ x ≤ 0.925 a mixed phase, O + R, region is achieved. In Chapter 4 of this thesis, the study of the space group assignment for the O phase based on the reflection conditions and microscopy studies is shown. By using the Maximum Entrophy Method / Rietveld method a six sites disordered model for the A-site has been built based on the charge density distribution using synchrotron X-ray diffraction (SXRD) data. A joint refinement using SXRD and neutron data was performed on composition x = 0.8 and the structure of this new polar phase crystallising in Pna21 with polarisation along [001]p has been solved. However, the O phase despite of being polar displays poor physical properties being the maximum piezoelectric coefficient obtained of 2.8 pC/N for x = 0.835 . In Chapter 5, preliminary structural analysis outcomes for the mixed phase, O + R, compositions with different polarisation directions along [001]p and [111]p respectively are shown along with their physical properties measurements results. By making solid solutions of BTFM and CTO, a maximum piezoelectric coefficient of 53 pC/N has been achieved for x = 0.835. This value is about two orders of magnitude greater than for BTFM (0.6 pC/N). A preliminary phase diagram of xBTFM-(1-x)CTO materials versus temperature has been built.
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MANFREDI, NORBERTO. "Synthesis and investigations of multifunctional organic molecules and materials for applications in the field of renewable energy." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2017. http://hdl.handle.net/10281/153280.
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In questo progetto di dottorato, abbiamo studiato nove molecole e materiali per applicazioni in celle solari di terza generazione e produzione fotocatalitica o fotoelettrochimica di H2. La prima parte di questo lavoro è stata focalizzata sullo studio di dispositivi DSSCs andando a studiare nuov fotosensibilizzatori a base organica, alcuni dei quali ottenuti da collaborazioni esterne, e diversi coloranti a base fenotiazinica recanti funzionalizzazioni differenti al fine di modularne proprietà ottiche e fotovoltaiche sia in presenza di elettroliti a base organica sia acquosa. celle solari a perovskiti (PSC) sono state studiate ed è stata sviluppata una procedura di fabbricazione affidabile. Uno studio di fattibilità circa l'integrazione in dispositivi multi-giunzione con mc-Si è stato fatto con successo. Diversi materiali di trasporto di lacune a base di idrazoni sono stati sintetizzati e le loro proprietà ottiche ed elettrochimiche sono state studiati. La mobilità dei portatori di questi nuovi materiali è stata studiata in transistor organici ad effetto di campo e sono stati impiegati in dispositivi PSC.Coloranti fenotiazinici ramificati, sono stati testati come fotosensibilizzatori nella produzione fotocatalitica di H2, in combinazione con un catalizzatore Pt / TiO2. Le proprietà ottiche ed elettrochimiche dei coloranti sono stati studiati, mostrando che un'attenta progettazione dei nuovi coloranti concessi migliorate proprietà ottiche. Nella produzione di H2 oltre 20 h, i nuovi sensibilizzatori rivelato stabilità migliorata dopo tempi di irraggiamento più lunghi e prestazioni migliorate, in termini di velocità di produzione H2 ed efficienze luce-combustibile, che sono stati per la prima volta associate ad una maggiore stabilità in produzione fotocatalitica H2 e all'assenza di degradazione del colorante.
Colorante fenotiazinico analogo è stato funzionalizzato con una unità di glucosio periferico (PTZ-GLU) per aumentare la sua affinità con l'acqua e migliorare fotogenerazione di H2. Rispetto al corrispondente derivato alchilico, nonché il comune idrofila trietilenico (PTZ-TEG); PTZ-GLU è due volte più efficiente di PTZ-TEG nel fotogenerazione di H2 in termini di gas evoluto e numero di turnover. PTZ-GLU è stato studiato in presenza di co-adsorbenti appositamente progettati a base di glucosio (GLU) per promuovere le interazioni direzionali sulla superficie catalitica semiconduttore e, accesso maggiore attività catalitica. Abbiamo dimostrato che l'uso combinato del colorante a base di glucosio e co-adsorbente prestata maggiore H2 fotocatalitico. Una serie di coloranti a base di carbazolo sono stati sintetizzati e utilizzati come fotosensibilizzatori nella generazione H2 fotocatalitico. Rispetto ai coloranti PTZ più comunemente utilizzati, lo sfruttamento della struttura planare e senza zolfo del carbazolo consentono un trasferimento di carica ligando-metallo (LMCT), aumentando la produzione di H2. Uno studio preliminare su coloranti p-type per la produzione di H2 da fotoelettrochimica è iniziato con risultati interessanti.In this PhD project, we studied molecules and new materials for application in third generation solar cells and photocatalytic or photoelectrochemical production of H2. The first part of this work was focused on the study of DSSCs devices going to investigate new organic-based photosensitizers, some of them obtained from external collaborations, and several phenothiazine based dyes bearing different functionalization to modulate optical and photovoltaic properties either in presence of organic and water based electrolyte. Perovskite solar cells (PSC) have also been studied and a reliable fabrication procedure have been developed. A study of feasibility about integration in multi-junction devices with mc-Si have been done successfully. Several hydrazone-based hole transport materials have been synthesized and their optical and electrochemical properties have been investigated. The mobility of carriers of these new materials have been studied in organic field effect transistor and they have been employed in PSC devices. Dibranched phenothiazine based dyes, were tested as photosensitizers in the photocatalytic production of H2, in combination with a Pt/TiO2 catalyst. The optical and electrochemical properties of the dyes were investigated, showing that careful design of the new dyes afforded enhanced optical properties. In the H2 production over 20 h, the new sensitizers revealed improved stability after longer irradiation times and enhanced performances, in terms of H2 production rates and light-to-fuel efficiencies, which were for the first time associated with enhanced stability under photocatalytic production of H2 and the absence of critical dye degradation. Analogous phenothiazine dye has been functionalized with a peripheral glucose unit (PTZ-GLU) to bust its affinity to water and enhance dye-sensitized photogeneration of H2. Compared to the corresponding alkyl derivative, as well as the common hydrophilic triethylene glycol substitution (PTZ-TEG); PTZ-GLU performed twice more efficient than PTZ-TEG in the photogeneration of H2 in terms of evolved gas and turnover number. PTZ-GLU has been investigated in presence of properly designed glucose-based co-adsorbents (GLU) to promote beneficial directional interactions on the semiconductor catalytic surface and, access enhanced catalytic activity. We have demonstrated that the combined use of the glucose-based dye and co-adsorbent afforded enhanced photocatalytic H2. A series of carbazole-based dyes have been synthesized and used as photosensitizers in the photocatalytic H2 generation. Compared to the more commonly used PTZ dyes, the exploitation of the planar and sulfur-free carbazole scaffold allows a ligand-to-metal charge transfer (LMCT) visible light absorption, busting the H2 production. A preliminary study on p-type dyes for H2 production by photoelectrochemistry has begun with interesting results.
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Blomdahl, Emil. "Synthesis and characterization of novel hybrid organic-inorganic materials." Thesis, KTH, Tillämpad fysikalisk kemi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-302288.
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Efterfrågan på bättre och mer hållbart material ökar. Mer effektivt material kommer att behövas för att möta den ökande, globala efterfrågan. Hybrida organiska-oorganiska material är en typ av material som har varit av stort intresse nyligen, och kan beskrivas som en typ av material som består av både organiska och oorganiska komponenter. Denna avhandling har fokuserat på hybrida organiska-oorganiska material inspirerade av den klassiska perovskitstrukturen ABX3, där komponent A är en organisk katjon, komponent B är en divalent metalkatjon och komponent X är en anjon. Hybrida organiska-oorganiska material som är utgår från den klassiska perovskitstrukturen kan ha olika funktionella egenskaper och en bred variation av tänkbara applikationer. Några exempel på dessa egenskaper och möjliga applikationer inkluderar god fotokonduktivitet för solceller, utmärkt emissionsegenskaper för ljusdioder och justerbara dielektriska egenskaper för elektroniska växlar och sensorer. De fysiska egenskaperna av det hybrida organiska-oorganiska materialet beror på kristallstrukturen av materialet, som i sig bestäms av valet av komponenter. På grund av de många möjligheter av organiska och oorganiska komponenter så finns det möjlighet att syntetisera helt nya hybrida organiska-oorganiska föreningar som kan ha nya eller förbättrade fysiska egenskaper. Nuvarande hybrida organiska-oorganiska material som utgår från perovskitstrukturen använder huvudsakligen bly som divalent metalkatjon, och det beror på att den ger den bästa funktionella effekten. Blys toxicitet är dock en stor nackdel för nuvarande blybaserade hybrid oorganiska material. Möjligheten att ersätta bly med en annan divalent metall har undersökts under detta projekt. I denna avhandling så har den organiska katjonen cyclohexylammonium (CHA) varit i fokus som den organiska komponenten. Målet med detta examensarbete var att designa, syntetisera och karakterisera nytt hybrid organisk-oorganiskt material. De hybrida organiska-oorganiska föreningarna CHAZnBr3 och (CHA)2ZnBr4 syntetiserades för den första gången, så vitt författaren vet, och kommer vara i fokus i denna avhandling. De två nya hybrida organiska-oorganiska föreningarna blev strukturellt karakteriserade med X-ray Diffraction (XRD) och termiskt karakteriserade med Thermal Gravimetric Analysis (TGA) och Differential Scanning Calorimetry (DSC). Den första föreningen, CHAZnBr3, kunde bestämmas att vara ortorombisk vid 298 K. Föreningen bestämdes vara termisk stabil upp till 490 K, och genomgår en fasövergång vid 445 K. Den andra föreningen, (CHA)2ZnBr4, kunde inte bestämmas strukturellt vid varken 100 K eller 298 K. Föreningen bestämdes vara termisk stabil upp till 490 K, och genomgår en fasövergång vid 230 K. Ytterligare karakterisering krävs för att bättre förstå egenskaperna hos dessa föreningar och deras möjliga användningsområden.The demand for better and more sustainable material is increasing. More efficient materials will be needed to meet the growing global need. Hybrid organic-inorganic materials are one type of materials that have been of great interest recently, which can be described as a class of materials that mix organic and inorganic components. This thesis focused on hybrid organic-inorganic materials inspired by the classical perovskite crystal structure ABX3, where component A is an organic cation, component B is a divalent metal cation and component X is an anion. Hybrid organic-inorganic materials based on the classical perovskite structure may have various functional properties and may have a broad range of potential applications. Some examples of those properties as well as some and possible applications include good photoconductivity and power conversion efficiency for photovoltaic devices, excellent emission properties for light emitting diodes and tunable dielectric properties for electronic switches and sensors. The physical properties of the hybrid organic-inorganic material are determined by the crystal structure of the material, which in turn will be decided by the choice of components. With the many possible choices for organic and inorganic components, there is an opportunity to synthesize completely new hybrid organic-inorganic compounds that may display new or superior physical properties. Current hybrid organic-inorganic materials based on the perovskite crystal structure mainly use lead as the divalent metal, since it currently gives the best performance. The toxicity of lead is a major drawback for current lead-based hybrid organic-inorganic materials. The possibility to replace lead with another divalent metal has been explored during this project. For this thesis, the organic cation cyclohexylammonium (CHA) has been of focus as the organic component. The aim of this thesis was to design, synthesize and characterize novel hybrid organic-inorganic compounds. The hybrid organic-inorganic compounds CHAZnBr3 and (CHA)2ZnBr4 were synthesized for the first time, to the best of our knowledge, and will be the focus of this thesis. The two new hybrid organic-inorganic compounds were structurally characterized by X-ray Diffraction (XRD) and thermally characterized by Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). The first compound, CHAZnBr3, could be determined to be orthorhombic at 298 K. The compound was found to be thermally stable up 490 K, and to undergo a phase transition at 445 K. The second compound, (CHA)2ZnBr4, could not be fully structurally solved at either 100 K or 298 K. The compound was found to be thermally stable up to 490 K, and to undergo a phase transition at 230 K. Further characterization will be needed to better understand the properties of these two compounds and their possible applications.
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Pack, Maria Joyce. "Complex metal oxide materials : synthesis, structural characterisation and development of combined EXAFS and powder differaction analysis." Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243098.
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