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1
Zhong, Zhimin. "Combustion syntheses and characterization of Barium Titanate, Barium Tetratitanate and Lead substituted Barium Tetratitanate /". The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487861396027028.
Testo completo
2
Rai, Maha. "Molecular dynamics modelling of barium silicate and barium fluorozirconate glasses". Thesis, University of Kent, 2018. https://kar.kent.ac.uk/66702/.
Testo completoAbstract (sommario):
Advancement in science and technology has profoundly depended on new types of glass innovation. The glasses that were studied in this project are binary barium silicate glasses, binary barium fluorozirconate glasses, ZBLAN glasses and 〖Eu〗^(3+) doped ZBLAN glass (the ZBLAN glasses are based on binary barium fluorozirconate glass). The high atomic number of barium in the barium silicate glasses provides high mass and high electron density providing its applications for heat and X-ray shielding. The phenomena such as phase separation in the barium silicate glass will affect its properties of durability and electrical conductivity. On the other hand, ZBLAN glasses have a broad infrared optical transmission window due to the weaker bonding/interaction of F^- ions. Due to the presence of lanthanum in the composition ZBLAN glass can be easily doped with rare-earth ions such as 〖Eu〗^(3+) giving it many optical applications such as optical amplifier and fibre lasers. Hence, it's essential to study the structure of these glasses to understand their properties for applications. This thesis used the classical molecular dynamics modelling technique to study the static atomic structure of glass. Generally, fluoride glasses can be formed by totally replacing oxygen atoms in oxide glasses by fluorine atoms. The oxide silicate glasses are common glasses that follow the Zachriasen rules of glass formation but the fluorozirconate glasses do not and lack fixed structural units. The structure analysis was performed at short-range order (e.g. coordination number, bond length and bond angle), medium-range order (e.g. network connectivity) and long- range order (e.g. phase separation). The related crystals were also simulated in similar conditions to the glasses to compare their atomic structure. Normally at short-range order glass structure is similar to its related crystal but the differences between them starts from the position and number of next nearest neighbours and increases thereafter. Additionally, the new methods such as rotational invariants and grid analysis were used to scrutinise structural units and phase separation respectively. The model of barium silicate glass shows good agreement with experimental diffraction data. The typical bond length and coordination number for Ba were 2.97 Å and approximately 7 respectively. The model did not show any phase separation at low Ba content and hence for further investigation very large models of alkaline earth silicate glasses were studied to see how Ba, Ca and Mg are distributed in the glass. The grid analysis was used to see the distributions which show homogeneity for Ba and Ca and inhomogeneity for Mg cation. The structural units of fluorozirconate glasses were carefully studied as they do not follow the Zachriasen glass model. The coordination number for Zr was mixture of 7 and 8. The rotational invariant analysis shows that the structural units of ZrF_n polyhedra for coordination number 7 and 8 were similar to Augmented Triangular Prism and Biaugmented Triangular Prism respectively. However, rotational invariant values for BaF_n polyhedra tend more towards random. The large complex model of 〖Eu〗^(3+) doped ZBLAN glass was made as it is studied for optical applications. The initial analysis was to observe whether Zr and Ba has similar structural roles as in binary fluorozirconate glass system which they do. Considering the extra elements in ZBLAN glass, Al behaves like a network former and has octahedra structural units whereas La and Na behave like modifiers. In the glass Eu was uniformly distributed with predominantly coordination number of 8 and does not have well defined structural units.
3
Kinsey-Nielsen, Susan Mary. "HIGH-RESOLUTION LASER SPECTROSCOPY OF BARIUM-MONOHYDROXIDE AND BARIUM-MONODEUTEROXIDE". Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/292080.
Testo completo
4
Kirby, Nigel Matthew. "Barium zirconate ceramics for melt processing of barium cuprate superconductors". Thesis, Curtin University, 2003. http://hdl.handle.net/20.500.11937/1364.
Testo completoAbstract (sommario):
The widespread use of high temperature superconductors through improved understanding of their underlying physics is in part dependent on the synthesis of large, high quality single crystals for physical research. Crucible corrosion is an important factor hindering the routine synthesis of large, high purity rare-earth barium cuprate superconductor single crystals. Molten BaCuO2-CuO fluxes required for the growth of such crystals are highly corrosive to substrate materials, and corrosion products may lead to chemical contamination of crystals and other practical difficulties. BaZrO3 is known to be inert to BaCuO2-CuO melts, but its use has remained restricted to a very small number of laboratories worldwide because it is very sensitive to the effects of off- stoichiometric or residual secondary phases which degrade its performance. BaZrO3 suitable for sustained melt containment is difficult to produce due to kinetic limitations of phase purity, difficulty in sintering to adequate density, and very narrow stoichiometry tolerances of finished ceramics. The existing literature provided a guide to the production of high quality BaZrO3, but was not sufficiently complete to readily allow production of crucibles suitable for this application. The two basic aims of this project were: To provide a comprehensive and quantitative description of the necessary attributes of crucibles for barium cuprate melt processing and to expand the knowledge of solid-state BaZrO3 processing to encourage its widespread application to crucible manufacture; To explore the application of solution chemical processes whose potential benefits could lead to routine application of BaZrO3 through improved ceramic quality and processing properties.Based primarily on solid-state processing research, the optimal stoichiometry for corrosion resistant crucibles was observed over the narrow range of 1.003±0.003 Ba : (Zr + Ht) mole ratio. Residual ZrO2 must be strictly avoided even at very low levels because severe localized expansion of Z a grains during reaction with the melt severely reduces corrosion resistance. Although the effect of Ba-rich phases are less severe, their abundance must be suppressed as much as allowed by the production process. Solid-state derived crucibles with a large barium excess were unstable and readily attacked by water. TEM analysis clearly showed residual Zr02 was present as discrete grains and not as grain boundary films, and also the prevalence of intragranular defects in Ba-rich ceramics. Quantitative knowledge of the narrow range of required stoichiometry is critical for developing successful solid-state and solution chemical processes. Reliably achieving the required stoichiometry and phase purity is experimentally challenging and beyond the capability of many processing systems. Systematic investigation revealed sharp changes in physical properties of processed powders across the phase boundary. The resistance of BaZrO3, of the desired stoichiometry to grain growth during powder processing has not previously been reported in the available literature. At the desired stoichiometry for corrosion resistance, powder grain growth resistance combined with very precise control over stoichiometry makes the solid-state process more competitive with solution-based processes than previously acknowledged in the literature. The development of solution processes for BaZr03 precursors is complicated by aqueous chemistry of zirconium compounds.This project developed the first chemically derived precursor process demonstrated to produce a ceramic of adequate quality for sustained barium cuprate melt containment. The barium acetate / zirconium oxychloride / ammonium oxalate system provided control over stoichiometry without requiring elevated solution temperatures, a large excess of barium reagents, or reagents containing alkalis. Despite showing the capability to supersede the solid-state process, the oxalate process still requires further refinement to more reliably achieve high sintered densities. Although the attributes required for sustained barium cuprate melt containment are now clear, its routine mass production remains reliant on further development of solution chemical techniques or improvements to the kinetics of solid-state processing. This project advanced ceramic design and processing technology in the BaZrO3 system and provided new approaches in meeting the challenging analytical needs of research and process control for high quality production of this compound.
5
Kirby, Nigel Matthew. "Barium zirconate ceramics for melt processing of barium cuprate superconductors". Curtin University of Technology, Department of Applied Physics, 2003. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=16216.
Testo completoAbstract (sommario):
The widespread use of high temperature superconductors through improved understanding of their underlying physics is in part dependent on the synthesis of large, high quality single crystals for physical research. Crucible corrosion is an important factor hindering the routine synthesis of large, high purity rare-earth barium cuprate superconductor single crystals. Molten BaCuO2-CuO fluxes required for the growth of such crystals are highly corrosive to substrate materials, and corrosion products may lead to chemical contamination of crystals and other practical difficulties. BaZrO3 is known to be inert to BaCuO2-CuO melts, but its use has remained restricted to a very small number of laboratories worldwide because it is very sensitive to the effects of off- stoichiometric or residual secondary phases which degrade its performance. BaZrO3 suitable for sustained melt containment is difficult to produce due to kinetic limitations of phase purity, difficulty in sintering to adequate density, and very narrow stoichiometry tolerances of finished ceramics. The existing literature provided a guide to the production of high quality BaZrO3, but was not sufficiently complete to readily allow production of crucibles suitable for this application. The two basic aims of this project were: To provide a comprehensive and quantitative description of the necessary attributes of crucibles for barium cuprate melt processing and to expand the knowledge of solid-state BaZrO3 processing to encourage its widespread application to crucible manufacture; To explore the application of solution chemical processes whose potential benefits could lead to routine application of BaZrO3 through improved ceramic quality and processing properties.Based primarily on solid-state processing research, the optimal stoichiometry for corrosion resistant crucibles was observed over the narrow range of 1.003±0.003 Ba : (Zr + Ht) mole ratio. Residual ZrO2 must be strictly avoided even at very low levels because severe localized expansion of Z a grains during reaction with the melt severely reduces corrosion resistance. Although the effect of Ba-rich phases are less severe, their abundance must be suppressed as much as allowed by the production process. Solid-state derived crucibles with a large barium excess were unstable and readily attacked by water. TEM analysis clearly showed residual Zr02 was present as discrete grains and not as grain boundary films, and also the prevalence of intragranular defects in Ba-rich ceramics. Quantitative knowledge of the narrow range of required stoichiometry is critical for developing successful solid-state and solution chemical processes. Reliably achieving the required stoichiometry and phase purity is experimentally challenging and beyond the capability of many processing systems. Systematic investigation revealed sharp changes in physical properties of processed powders across the phase boundary. The resistance of BaZrO3, of the desired stoichiometry to grain growth during powder processing has not previously been reported in the available literature. At the desired stoichiometry for corrosion resistance, powder grain growth resistance combined with very precise control over stoichiometry makes the solid-state process more competitive with solution-based processes than previously acknowledged in the literature. The development of solution processes for BaZr03 precursors is complicated by aqueous chemistry of zirconium compounds.
This project developed the first chemically derived precursor process demonstrated to produce a ceramic of adequate quality for sustained barium cuprate melt containment. The barium acetate / zirconium oxychloride / ammonium oxalate system provided control over stoichiometry without requiring elevated solution temperatures, a large excess of barium reagents, or reagents containing alkalis. Despite showing the capability to supersede the solid-state process, the oxalate process still requires further refinement to more reliably achieve high sintered densities. Although the attributes required for sustained barium cuprate melt containment are now clear, its routine mass production remains reliant on further development of solution chemical techniques or improvements to the kinetics of solid-state processing. This project advanced ceramic design and processing technology in the BaZrO3 system and provided new approaches in meeting the challenging analytical needs of research and process control for high quality production of this compound.
6
Lehnen, Peer. "Relaxoreigenschaften von Strontium-Barium-Niobat - Relaxor Properties of Strontium-Barium-Niobate". Gerhard-Mercator-Universitaet Duisburg, 2001. http://www.ub.uni-duisburg.de/ETD-db/theses/available/duett-12132001-102821/.
Testo completoAbstract (sommario):
In the present thesis the relaxor properties of the tungsten-bronze ferroelectric material strontium-barium niobate Sr1-wBawNb2O6 (SBN) are investigated. SBN is a very good experimental realization of the three-dimensional random-field Ising model (3d RFIM). The quenched random fields (RF) originate from charge disorder and can be enhanced by doping with Ce3+. They are responsible for the formation of polar nanoclusters in the paraelectric phase. In order to study the critical behavior of SBN, linear birefringence (LB) and second harmonic generation (SHG) have been measured as a function of temperature. Within an Ornstein-Zernike analysis of the LB data the autocorrelation function, <P2>, was determined, whereas the dipolar correlation length was obtained from the SHG data. They suggest that, due to its intrinsic disorder, pure SBN does not belong to the 3d Ising universality class. Doping with Ce3+ions, which seem to generate RFs, enhances the relaxor properties. The critical exponents v and y of SBN:Ce shift against those of the 3d RFIM. The domain morphology of SBN:Ce has been investigated by piezoelectric force microscopy (PFM). Fractal-like shaped zero-field cooled nanodomains are observed. Their size distribution can be described by a power law with exponential cutoff in accordance with prediction for the RFIM. It was measured for the first time in a RF system. The temperature and field induced evolution of natural and written domains has been studied with PFM, LB and SHG measurements. It reveals a very slow relaxation from a macrodomain into a depolarized multidomain state (and vice versa) even above TC. This hints at strong pinning forces due to quenched RFs. They are also responsible for the observed aging in poled SBN and the field induced cluster percolation above TC measured with SH-hysteresis. The domains can be considered as a "thick" phase grating for SH-diffraction. The Bragg-regime diffraction efficiency reflects the temperature and field induced change of the averaged domain sizes in the system.
7
Maie, Hiroki. "Synthesis and dielectric properties of nanocrystalline barium titanate and silver/barium titanate particles". Connect to this title online, 2008. http://etd.lib.clemson.edu/documents/1211387100/.
Testo completo
8
Nabasenja, Caroline. "Radiation doses for barium meals and barium enemas in the Western Cape South Africa". Thesis, Cape Peninsula University of Technology, 2009. http://hdl.handle.net/20.500.11838/1560.
Testo completoAbstract (sommario):
Thesis submitted in fulfilment of the requirements for the award of the
degree of
Master of Technology Radiography (Diagnostic)
in the Faculty of Health and Wellness Sciences
at the Cape Peninsula University of Technology
2009Since their discovery in 1895, the use of x-rays is continuously evolving in medicine making the diagnosis of injuries and diseases more practicable. It is therefore not surprising that x-rays contribute 90% of the radiation dose to the population from manmade sources (DWP, 1992). Moreover, these radiation doses are associated with both fatal and non-fatal cancer risk that is detrimental to adults between 20 to 60 years (Wall, 1996). Radiation dose to individuals therefore needs to be actively monitored in order to minimise such risk. Barium contrast examinations were characterised as one of the radiological examinations that contributed enormously to the collective dose to the patients in the radiology department (DWP, 1992). Determining the diagnostic reference levels of such examinations would reduce the over-exposure of individuals to ionising radiation. Currently in South Africa (SA), there are no diagnostic dose reference levels for barium meal (BaM) and barium enema (BaE) examinations. This study therefore investigated the radiation doses delivered to patients referred for BaM and BaE, obtained potential regional reference doses for these examinations, compared the radiation doses obtained with those from similar dosimetry studies and investigated sources of dose variation among the study sites. A total of 25 BaM and 30 BaE patients in the age range 18 to 85 years, weighing 50 kg to 90 kg, at 3 hospitals in the Western Cape, SA were investigated. The radiation dose to the patients was measured using Dose Area Product (DAP) meters that were permanently fitted onto fixed fluoroscopy units at these 3 hospitals. The third quartile DAP values were 20.1 Gycm2 and 36.5 Gycm2 for BaM and BaE respectively. The median DAP values were 13.6 Gycm2 and 27.8 Gycm2 for BaM and BaE respectively. The median values were recommended as the potential Diagnostic Reference Levels for BaM and BaE as they are less affected by outlying values of under or over- weight (Yakoumakis, Tsalafoutas, Sandilos, Koulentianos et al, 1999). The weights of the patients, fluoroscopy time, the number of images obtained, the use of digital or conventional fluoroscopy equipment and the level of training of the radiologists were the factors considered for dose variation among the 3 hospitals.
9
Jakubek, Zygmunt J. (Zygmunt Jerzy). "Rydberg spectroscopy of barium monofluoride". Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/32154.
Testo completo
10
Yang, Yaodong. "Barium Titanate-Based Magnetoelectric Nanocomposites". Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/38666.
Testo completoAbstract (sommario):
Barium Titanate (BaTiO3 or BTO) has attracted an ever increasing research interest because of its wide range of potential applications. Nano-sized or nanostructured BTO has found applications in new, useful smart devices, such as sensors and piezoelectric devices. Not only limited to one material, multi-layers or multi-phases can lead to multifunctional applications; for example, nanocomposites can be fabricated with ferrite or metal phase with BTO. In this study, I synthesized various BTO-ferrites, ranging from nanoparticles, nanowires to thin films. BTO-ferrite coaxial nanotubes, BTO-ferrite self-assemble thin films, and BTO single phase films were prepared by pulsed laser deposition (PLD) and sol-gel process. BTO-ferrite nanocomposites were grown by solid state reaction. Furthermore, BTO-metal nanostructures were also synthesized by solid state reaction under hydrogen gas which gave us a great inspiration to fabricate metal-ceramic composites.
To understand the relationship between metal and BTO ceramic phase, I also deposited BTO film on Au buffered substrates. A metal layer can affect the grain size and orientation in BTO film which can further help us to control the distribution of dielectric properties of BTO films.
After obtaining different nanomaterials, I am interested in the applications of these materials. Recently, many interesting electric devices are developed based on nanotechnology, e.g.: memristor. Memristor is a resistor with memory, which is very important in the computer memory. I believe these newly-synthesized BTO based nanostructures are useful for development of memristor, sensors and other devices to fit increasing needs.Ph. D.
11
Gross, Timothy M. "[Beta]-barium borate thin film formation on silicon through metal organic decomposition of two novel precursors, barium dimesitylborinate and barium (18-crown-6) cyclotriboroxane /". Online version of thesis, 2004. http://hdl.handle.net/1850/11802.
Testo completo
12
Janasi, Suzilene Real [UNESP]. "Ferrita de bário: preparação de fases dopadas com cobalto, titânio e estanho". Universidade Estadual Paulista (UNESP), 1997. http://hdl.handle.net/11449/102592.
Testo completoAbstract (sommario):
Made available in DSpace on 2014-06-11T19:32:11Z (GMT). No. of bitstreams: 0
Previous issue date: 1997Bitstream added on 2014-06-13T20:27:17Z : No. of bitstreams: 1
janasi_sr_dr_araiq.pdf: 2566763 bytes, checksum: e10173459cbf62287b0478669d7c6ed0 (MD5)A substituição parcial de íons Fe3+ por pares de íons (Co2+-Ti4+ ou Co2+-Sn4+) na ferrita de bário hexagonal (BaFe12O19) leva a uma substancial diminuição no campo coercitivo (Hc) com uma pequena mudança na magnetização de saturação (Ms), permitindo seu uso em gravação magnética e magneto-óptica de alta densidade. Os diferentes métodos de preparação de ferritas de bário resultam em produtos com propriedades distintas. Neste trabalho, preparou-se BaFe12-2xCoxTixO19 e BaFe12-2xCoxSnxO19 (0,25 £ x £ 1) por coprecipitação, utilizando cloretos dos metais precursores e solução de KOH/K2CO3 como precipitante. Após a secagem, o produto obtido foi calcinado a 950oC por 3h, lavado e seco. Os difratogramas de raios X indicaram a formação da ferrita de bário. As micrografias eletrônicas de varredura mostraram que os pós obtidos apresentam-se na forma de plaquetas hexagonais de 1 a 2mm. As curvas de magnetização das ferritas de bário dopadas mostraram que o campo coercitivo e a remanência diminuem em função do aumento da razão de substituição x. A curva de magnetização da amostra dopada com Co-Ti, com x = 1 é característica de uma ferrita mole, com Hc = 13,5 kA.m-1 (0,17 kOe), Ms = 46,1 emu.g-1 e Mr = 11,0 emu.g-1. Para a amostra dopada com Co-Sn a diminuição de Mr não é significante. Estes resultados mostraram que as propriedades magnéticas das ferritas de bário dopadas obtidas por coprecipitação foram melhoradas, em relação aos dados da literatura para ferrita de bário pura ou dopada.
The partial substitution of Fe3+ ions with pairs of ions (Co2+-Ti4+ or Co2+-Sn4+) in hexagonal barium ferrite (BaFe12O19) leads to a substantial reduction on coercivity (Hc) with only a low change in saturation magnetization (Ms), allowing its use in high density magnetic and magneto-optical recording. Different preparative methods result in barium ferrites with distinguished properties. In this work, BaFe12-2xCoxTixO19 and BaFe12-2xCoxSnxO19 (0.25 £ x £ 1) were prepared by the coprecipitation method using chloride salt precursors and KOH/K2CO3 solution. After drying, the powder was calcinated at 950oC by 3 h, washed and dried. The X ray diffraction patterns indicated the barium ferrite phase formation. The scanning electron micrographs showed that the particles are hexagonal platelike with diameter size ranging from 1 to 2 mm. The magnetization curves of substituted barium ferrites showed that the values of Hc and Mr decrease with the increase of the substitution ratio x. The magnetization curve profile for Co-Ti substituted sample with x =1 is characteristic of a soft ferrite with Hc = 13.5kA.m-1 (0.17 kOe), Ms = 46.1 emu.g-1 and Mr = 11.0 emu.g-1. These results indicated that the magnetic properties of substituted barium ferrites obtained by coprecipitation were improved when compared with the literature data for pure and substituted barium ferrite.
13
Lee, Chung-Kook. "Crystallization of Nano-sized barium ferrite". Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/19920.
Testo completo
14
Cannell, David Stuart. "The electric strength of barium titanate". Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.237676.
Testo completo
15
Quadros, da Cunha Feteira AntoÌnio Manuel AndreÌ. "Characterisation of barium titanate based ceramics". Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407525.
Testo completo
16
Abdulla, Sarah Ahmed Eltayed. "Barium sulphate : problems, solutions and applications". Thesis, University of Surrey, 2010. http://epubs.surrey.ac.uk/848627/.
Testo completoAbstract (sommario):
The main aim of this work is to synthesise barium sulphate (BaS04) that are tiny in size (nanoparticles). BaS04 scaling is a known problem in the context of offshore oil recovery. Different methods of scale control have been suggested in the literature, none has solved the BaS04 scaling problem dramatically. In this work several methods were assessed, but only one of them seemed to work well. The methods studied were: 1) Formation of colloidal BaS04 in an aqueous alcohol medium using BaCh and Na2S04 as precursors. The precursors were mixed rapidly forming rhombohedral BaS04 and by tubular reactor forming dendrite-like particles. 2) Inhibition of Ba2+ using phosphino (carboxylic acids)prior to the sol- addition induced the formation of broom-stick-like BaS04 particles. 3)Formation of BaS04 microemulsions using different surfactants. Cationic surfactants (sodium bis-2-thylhexylsulfosuccinate) (AOT) induced the formation of BaS04 platelets and nanofilaments. While non-ionic surfactants (polyoxyethylene-4-dodecyl ether)(C12E04) and SEs different HLB values (2,6,15 and 16), induced the formation of BaS04 platelets with the former and BaS04 nanobaguettes with HLB 2 and platelet-like particles,defined nanorods and interconnected nanoparticles with HLB 6, 15 and 16 respectively. TX-lOO (polyethylene glycol p(1,1,3,3-tetramethylbutyl)- phenylether) formed small BaS04 nanoparticles. Anionic didodecyldimethylammonium bromide (DDAB) formed cylindrical BaS04 nanoparticles. 4) (SOl) in H20 was added to Ba2+ adsorbed on Stober silica producing spherical BaS04 nanoparticles in StOber silica spheres. 5) Ba2 + in H20 was added to (SOl)/AIO(OH). This is a new method to the best of our knowledge. It formed small BaS04 nanoparticles at 2 and 4 J.lmol (BaCh and Na2S04) and big bow-tie structured BaS04 particles at 6 J.lmol concentration per 5cm3 of AIO(OH). Since BaSOJAIO(OH) produced with SOlIAIO(OH)(aq) + Ba2+(aq) showed higher yields its scaling inhibition efficiency was studied in detail at three different concentrations of Ba2+ (64, 90 and 121 ppm) at 298 K and 320 K. This novel approach to scale control using chaperoning AIO(OH) is promising. A comparison study using 2-D imaging took place in BaS04 in AIOOH and BaS04 in H20 showed that the former remained longer as a sol. This suggests that BaS04 based in AIOOH can be used in medical diagnosis. BaS04 in AIOOH was used as a catalyst (prior to freeze drying) in an exhaust engine to test its efficiency in detoxifying the exhaust engine from CO, HC and NO" under stoichiometric conditions. Catalytic activates were also investigated after activation with Pt and Au.
17
Johnston, Diane E. "Characterisation of lanthanum-doped barium titanate". Thesis, University of Aberdeen, 1993. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU554634.
Testo completoAbstract (sommario):
One significant application of donor doped barium titanate (BaTiO3) is in the manufacture of Positive Temperature Coefficient of Resistance (PTCR) thermistors. Combined synthesis, phase diagram and electrical studies were undertaken on donor doped barium titanate with a view to understanding the factors responsible for PTCR phenomena. A range of materials, both commercial PTCR devices and in-house lanthanum-doped barium titanate samples, have been studied. All three commercial PTCR samples measured were found to be electrically inhomogeneous with two PTCR-exhibiting regions and a conductive grain core. The conductive core resistance had a characteristic temperature dependence, with a minimum occurring in the vicinity of the tetragonal to cubic phase transition (Tc) of barium titanate. The phase relations and electrical behaviour of two joins in the lanthanum-doped BaTiO3 system, join A (Ba4-4xLa4xTi4-xO12) and join B (Ba1-yLayTiO3+), were also studied. Compositions on joins A and B for 0x0.195 and 0y0.1 respectively, crystallised as single phase barium titanate. Charge compensation on both joins (at these concentrations) was achieved by a mixture of both titanium vacancies and free electrons. The electron compensation mechanism, Ba_1-yLa_yTi. 4+_1-yTi. 3+O_3, significantly complicates determination of phase relations in this system, since it occurs off the BaO-TiO_2-La_2O_3 ternary phase diagram. Ac impedance measurements indicated that samples on join A were electrically inhomogeneous resulting in the presence of different regions with variable Tx values; furthermore, the phase transitions in each region were themselves complex. The tetragonal to cubic phase transition was studied by a combination of x-ray diffraction, ac impedance and by varying dopant concentration. The resulting behaviour was complex, with both first order and continuous transitions occurring. There was also evidence of a two phase, (i.e. both cubic and tetragonal barium titanate) region associated with a distribution in particle size: small particles (&60 2m) were cubic; larger ones were tetragonal. It is apparent that the combined, complicating effects of grain size and segregation phenomena make it inappropriate to give an explanation for the phase relations and electrical behaviour of lanthanum-doped barium titanate in terms of classical phase equilibria and phase transition theories.
18
Smetana, Volodymyr. "Subnitride im System Alkalimetall-Barium-Stickstoff". [S.l. : s.n.], 2008. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-36312.
Testo completo
19
De, Palatis Michael V. "Production of cold barium monohalide ions". Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50251.
Testo completoAbstract (sommario):
Ion traps are an incredibly versatile tool which have many applications throughout the physical sciences, including such diverse topics as mass spectrometry, precision frequency metrology, tests of fundamental physics, and quantum computing. In this thesis, experiments are presented which involve trapping and measuring properties of Th³⁺. Th³⁺ ions are of unique interest in part because they are a promising platform for studying an unusually low-lying nuclear transition in the 229Th nucleus which could eventually be used as an exceptional optical clock. Here, experiments to measure electronic lifetimes of Th³⁺ are described. A second experimental topic explores the production of sympathetically cooled molecular ions. The study of cold molecular ions has a number of applications, some of which include spectroscopy to aid the study of astrophysical objects, precision tests of quantum electrodynamics predictions, and the study of chemical reactions in the quantum regime. The experiments presented here involve the production of barium monohalide ions, BaX⁺ (X = F, Cl, Br). This type of molecular ion proves to be particularly promising for cooling to the rovibrational ground state. The method used for producing BaX⁺ ions involves reactions between cold, trapped Ba⁺ ions and neutral gas phase reactants at room temperature. The Ba⁺ ion reaction experiments presented in this thesis characterize these reactions for producing Coulomb crystals composed of laser cooled Ba⁺ ions and sympathetically cooled BaX⁺ ions.
20
Thorner, Gentien. "Nanostructures de titanate de Baryum : modélisation,simulations numériques et étude expérimentale". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLC093/document.
Testo completoAbstract (sommario):
Des simulations numériques conduites sur un ferroélectrique, le Titanate de Baryum, permettent d'extraire les températures où se produisent les transitions pour chacune des composantes et elles utilisent le plus souvent des conditions limites périodiques. Cependant, il est possible de modifier la simulation de manière à rendre compte d'une particule isolée, et les conditions limites électriques de type court-circuit ou bien circuit ouvert affectent alors le résultat. Réduire la taille accorde encore davantage d'importance à de tels effets de surface par rapport aux effets de volume. Expérimentalement, la formation de nanocubes creux ou de nanotores a été observéelors de synthèses solvothermales. De possibles mécanismes de morphogénèse sont évoqués. Dans ce travail, les simulations ont ensuite été conduites sur des particules nanométriques, dont les formes avaient été obtenues expérimentalement. Pour des cubes creux, il a été constaté que la taille de l'inclusion vide modifiait la valeur du coefficient d'écrantage critique à partir duquel le comportement de la polarisation passe d'une configuration de type court-circuit à une configuration de type circuit fermé. Pour des nanotores aux basses températures, une modification du rapport entre petit et grand rayon donne lieu à des configurations possédant un moment toroïdal seul ou accompagné d'un moment hypertoroïdal voire d'oscillations de ce dernierNumerical simulations performed on a ferroelectric, Barium Titanate, yield all the transition temperatures under periodic boundary conditions. However, the same simulation can be modified to model an isolated particle under short-circuit or opencircuit electrical boundary conditions. Reducing size makes these surface effects even more important with regard to volume effects.From an experimental point of view, solvothermal synthesis of hollow nanocubesand nanotori is reported and various morphogenesis mechanisms are listed.In this work, simulations were performed on nanometric particles that had experimentally obtained shapes. In hollow cubes, it was shownthat the hole size changed the numerical value of the critical screening coefficient at which the system changes its behavior from aconfiguration that is short-circuit like to another one that is open-circuit like. For nanotori at low temperatures, a modification of the ratio between torus minor and major radius gives either configurations with only toroidalmoment or configurations in which it coexists with homogeneous or oscillating hypertoroidal moment
21
Kaur, Mehar. "The Terrestrial Biogeochemical Cycle of barium: A proposed study to examine barium flux in Mojave Desert dust". Scholarship @ Claremont, 2013. http://scholarship.claremont.edu/scripps_theses/150.
Testo completoAbstract (sommario):
Barium is a relatively abundant element in the crustal environments, Ba quantities can range from anywhere between 200ppm to 900ppm. Most common forms of Ba-minerals found in the environment are barite (BaSO4), witherite (BaCO3) and hollandite (Ba2Mn8O16). Ba is a useful element; it is used in various industries as a component in drilling fluids, in medical research and in manufacturing of various substances such as glass, ceramics, printing paper etc. However high quantity of Ba can be potentially toxic for the human body and can impair plant growth. It is therefore, important to review the terrestrial biogeochemical cycle of Ba, which is less studied and less understood than the oceanic biogeochemical cycle of Ba. Additionally, terrestrial systems face a diverse climate and are not as stable as the oceanic systems. Due to this the terrestrial biogeochemical cycle of barium is continuously changing and is more dynamic than the oceanic cycle. By studying one part of the cycle, i.e. the interaction of Ba in the atmosphere with the geosphere in the Mojave desert, NV, I propose a study to test the hypothesis that occurrence of, Ba-mineral, barite, in desert soils is mainly driven by dust flux. The proposal includes methodology for dust collection, sample analysis using XRF, XRD and SEM.EDS techniques and potential budget and timeline. Evidence supporting this claim would suggest that dust transports such minerals, affects the soil chemistry of desert soils and the interaction of various terrestrial systems.
22
Niggli, Stefan. "Klassische und laser-spektroskopische Untersuchungen an Barium /". [S.l.] : [s.n.], 1987. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=8416.
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Wu, Wenzhong. "Low Temperature Sintering Semiconductive Barium Strontium Titanate". FIU Digital Commons, 2007. http://digitalcommons.fiu.edu/etd/76.
Testo completoAbstract (sommario):
Low temperature sintering has become a very important research area in ceramics processing and sintering as a promising process to obtain grain size below 100nm. For electronic ceramics, low temperature sintering is particularly difficult, because not only the required microstructure but also the desired electronic properties should be obtained. In this dissertation, the effect of liquid sintering aids and particle size (micrometer and nanometer) on sintering temperature and Positive Temperature Coefficient Resistivity (PTCR) property are investigated for Ba1-xSrxTiO3 (BST) doped with 0.2-0.3mol% Sb3+ (x = 0.1,0.2,0.3,0.4 and 0.5). Different sintering aids with low melting point are used as sintering aids to decrease the sintering temperature for micrometer size BST particles. Micrometer size and nanometer size Ba1-xSrxTiO3 (BST) particles are used to demonstrate the particle size effect on the sintering temperature for semiconducting BST. To reduce the sintering temperature, three processes are developed, i.e. 1 using sol-gel nanometer size Sb3+ doped powders with a sintering aid; 2 using micrometer size powders plus a sintering aid; and 3 using nanometer size Sb3+ doped powders with sintering aids. Grain size effect on PTCR characteristics is investigated through comparison between micrometer size powder sintered pellets and nanometer size powder sintered pellets. The former has lower resistivity at temperatures below the Curie temperature (Tc) and high resistivity at temperatures above the Curie temperature (Tc) along with higher ñmax/ñmin ratio (ñmax is the highest resistivity at temperatures above Tc, ñmin is the lowest resistivity at temperatures below Tc), whereas the latter has both higher ñmax and ñmin. Also, ñmax/ñmin is smaller than that of pellets with larger grain size. The reason is that the solid with small grain size has more grain boundaries than the solid with large grain size. The contribution z at room temperature and high temperature and a lower ñmax/ñmin ratio value.
24
Gallagher, Andrew James. "Modelling barium isotopes in metal-poor stars". Thesis, University of Hertfordshire, 2012. http://hdl.handle.net/2299/9224.
Testo completoAbstract (sommario):
The principal theory concerning the origin of the elements heavier than the Fe-peak, such as Ba, strongly suggest that for old, metal-poor environments, the rapid (r-) process is the most likely path taken in their synthesis, while the slow (s-) process becomes more substantial in younger, more metal-rich stellar populations. In this work I test this theory by evaluating the isotope ratios of Ba. It is understood that Ba consists of seven stable isotopes, five of which are synthesised by the two neutron-capture processes. The two odd isotopes, 135,137Ba, as well as 138Ba are synthesised via both the r- and s-processes while two of the even isotopes, 134,136Ba are synthesised via the s-process only. The relative contribution of the r- and s-process to these isotopes can be understood via nucleosynthesis calculations and is described using the parameter fodd, where fodd = [N (135Ba) + N (137Ba)] /N (Ba). Low values of fodd (~0.11) indicate an s-process regime, while high values of fodd (~0.46) indicate an r-process regime. In the Ba II 4554 A line the even isotopes lie close to the line centre, while the odd isotopes, which are hyperfine split because of their non-zero nuclear spin, lie in the wings of the line. From an analysis of the line profile shape, one can determine whether Ba has been synthesised primarily through the r-process or s-process; a broad, asymmetric line would indicate a high r-process contribution, while a line with a deeper core and shallower wings would indicate a high s-process contribution. Using the radiative transfer code ATLAS, which assumes local thermodynamic equilibrium (LTE) and employs 1-dimensional (1D) KURUCZ06 model atmospheres, I synthesised line profiles for six metal-poor stars: HD140283, HD122563, HD88609, HD84937, BD-04 3208 and BD+26 3578 - for a range of isotope ratios. All six are of sufficiently low metallicity that Ba was expected to have an r-process origin. These were fit to high resolution (R\equiv \lamda/\Delta\lamda = 90 000 - 95 000), high signal-to-noise to the Ba II 4554 A line which has multiple components. In the first test, synthetic spectra were computed using the non local thermodynamic equilibrium (NLTE) radiative transfer code MULTI. The synthetic line profiles were fit to a number of lines in HD140283. Although this technique might have improved the fit in the line core, it was found that such a treatment did not improve upon fitting errors associated with the best fit 1D LTE synthetic profiles. The second test used a 3-dimensional (3D) radiative transfer code (LINFOR3D) that employed 3D, time-dependent atmospheres produced with CO5BOLD. The 3D synthetic pro les were fit to a selection of Fe lines and improvements over the poor fits produced by the 1D LTE synthesis were seen. It was found that the 3D synthesis could almost completely reproduce the line asymmetries seen in the observed stellar spectrum. This result suggests that further work to refine the 3D calculations and synthesis code would be valuable.
25
Wegmann, Markus Rolf. "Microextrusion of barium titanate for PTCR applications". Thesis, University of Strathclyde, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248863.
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Cui, Yongfei. "Ferroelectric barium titanate for semiconductor photocatalytic application". Thesis, Queen Mary, University of London, 2015. http://qmro.qmul.ac.uk/xmlui/handle/123456789/9530.
Testo completoAbstract (sommario):
Semiconductor photocatalysis has received extensive attention due to its wide applications in water and indoor air purification, solar fuel production, etc. Charge carrier separation is a crucial step in semiconductor photocatalysis and influences the overall efficiency. It has been demonstrated that internal depolarisiation field of ferroelectric materials can drive spatial separation of charge carriers, which results in spatial separation of reduction and oxidation reactions, and improved charge carrier separation. In this thesis, ferroelectric barium titanate was chosen and its photocatalytic performance in decolourisation of organic dye molecules was investigated. Photodeposition method was adopted to deposite silver nanoparticles on the surface of barium titanate. Silver modified barium titanate showed increased photodecolourisation rate compared with bare barium titanate due to its role of electron traps and hindered charge carrier recombination. A simple thermal treatment was used to alter the phase composition of the as-received barium titanate. Samples which contained more ferroelectric tetragonal phase were found to possess higher photocatalytic activity compared with non-ferroelectric samples. This was associated with stronger ferroelectricity after thermal treatment, which enhanced dye molecule adsorption and aid charge carrier separation. The mechanism and intermediates generated in photodegradation of Rhodamine B with silver modified ferroelectric barium titanate were studied. Cleavage of chromophore was demonstrated to dominate in the initial process. Benzoic acid was identified as the main intermediate and no siginificant discrepancy in intermediates distribution between ferroelectric photocatalytic system and non-ferroelectric system was observed. The influence of ferroelectric dipole of barium titanate on photocatalytic activity of heterostructured barium titanate/hematite was also studied. The synthesised heterostructured barium titanate/hematite showed higher photodcolourisation rate than both barium titanate and hematite. This phenomenon was attributed to the improved charge carrier separation and extended charge carrier lifetime arising from heterojunction and an interaction between the ferroelectric dipole and the carriers in the hematite.
27
Lea, David Wallace. "Foraminiferal and coralline barium as paleoceanographic tracers". Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/54332.
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28
Jette, Bruce Donald. "Feasibility of electrodeposition of yttrium and barium". Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/79452.
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29
Fallon, Joseph John. "Multiscale theory and simulation of barium titanate". Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/28089.
Testo completoAbstract (sommario):
Although barium titanate is one of the most widely studied ferroelectric materials, questions about the nature of its phase transition remain. There are two competing models for this transition (displacive and order-disorder) and experiments detect signs of both types of transition. To study this issue computationally requires the simulation of large, disordered systems on the atomic scale. In this PhD I have developed a new classical force field for BaTiO3 which, in essence, is an ionic model. The free parameters within this force field were fitted to data generated from density-functional theory (DFT) simulations. Properties that were not used in the fitting procedure calculated with the resulting force field were found to be in excellent agreement with those calculated via DFT. The potential energy surface of BaTiO3 has been explored in detail using DFT and the force field, enabling both sublattice and single ion displacements to be studied, and highlighting in particular the important role played by the oxygen ions. Dynamical simulations show behaviour compatible both with experiments that have been interpreted as evidence for displacive transitions and with experiments interpreted as evidence for order-disorder transitions. In particular, when the local structure of the phases was studied, the locations of the ions were found to be consistent with a displacive model, whereas the calculated distribution of polarisation densities was more characteristic of an order-disorder model. The direction of the local relative displacements of titanium and oxygen ions was also considered. The deviation of this displacement from the < 111 > directions produced excellent agreement with experimental measurements of the tetragonal phase, and a similar effect was found in the orthorhombic phase. These dynamical simulations were found to be very sensitive to a range of factors such as supercell size.
30
Fathi, Ariya Reza. "Barium Solidification/Stabilization of Legacy Fly Ash". University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1523014706886586.
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31
Fung, Sing Chor. "Conductivity fluctuations in yttrium barium cooper oxides". HKBU Institutional Repository, 1994. http://repository.hkbu.edu.hk/etd_ra/34.
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32
Rauch, William L. "Fabrication and properties of barium cerate based electrolytes". Thesis, Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/19638.
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33
Yobregat, Elsa. "Les isotopes du strontium et du baryum dans le Système Solaire précoce". Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEN002/document.
Testo completoAbstract (sommario):
Des anomalies nucléosynthétiques ont été observées dans des météorites pour plusieurs éléments. L’ampleur de ces anomalies ainsi que leur répartition entre les objets du système solaire renseigne sur le degré d’hétérogénéité de la nébuleuse solaire. L’étude des phases porteuses de ces anomalies procure des informations sur les processus à l’origine de cette hétérogénéité. Les datations par radiochronomètres de courte période reposent sur la répartition hétérogène des éléments père et fils. L’utilisation de ces outils nécessite donc l’étude parallèle des variations nucléosynthétiques de ces élémentsNucleosynthetic anomalies have been observed in meteorites for many elements. The magnitude and repartition of these anomalies provide information about the degree of heterogeneity of the solar nebula. The study of the nucleosynthetic anomalies carriers could also give insight into the processes responsible for this heterogeneity. The presence or absence of small variations in nucleosynthetic processes is a key for the use of the short-lived radiochronometers. Small variations in the repartition of the parent or daughter isotope can lead to misinterpretations of relative ages
34
SUBRAMANIAM, SRINIVAS. "EFFECTS OF PROCESSING ON PTCR BARIUM TITANATE SYSTEMS WITH BARIUM OXIDE AND TITANIUM OXIDE ADDITIONS IN THE NEAR STOICHIOMETRIC REGION". University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1047057044.
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35
Janowski, Mary Patricia. "An investigation of the high barium oxide portion of the BaO-Sc₂O₃-Al₂O₃ ternary phase diagram". Thesis, Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/19414.
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36
Aydogan, Eda. "Processing And Characterization Of Textured Barium Ferrite Ceramics". Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614465/index.pdf.
Testo completoAbstract (sommario):
Technological advances results in the fact that quite a large number of electronic equipment interacts with its environment leading to the malfunction of the devices. This brings about the necessity of using proper electromagnetic (EM) wave absorbers/shields to avoid such interactions. In order to absorb EM waves in a large frequency band from several MHz to GHz, barium hexaferrite (BaHF) ceramics which are produced as textured ceramics as well as in multilayered form can be used. Textured ceramics are processed by tape casting using templated grain growth (TGG) phenomenon. In order to obtain textured ceramics, BaHF powders and platelets are required as raw materials in such a way that during sintering small size powders are directioned by large platelet surfaces. In this study, ferrite powders were synthesized by mixed oxide technique while the platelets were produced by both molten salt synthesis (MSS) and reactive templated grain growth (RTGG) methods. In the case of platelet synthesis by MSS, effects of calcination temperature and time as well as type and composition of the flux on the formation and morphology of platelets were investigated based on the XRD and SEM results. Studies have shown that KCl flux led to the formation of sharper platelet morphology, while NaCl resulted in more round shapes. However, extent of BaHF formation in the case of NaCl was higher when compared to KCl flux due to its higher wettability characteristic, and hence faster interaction with the raw materials. Since the aspect ratio of the synthesized platelets was only ca. 2-4, these platelets were not efficient for further TGG studies. Alternatively, BiFeO3 (BiF) particles having ~30-40 &mum average size were synthesized as seed crystals for the synthesis of BaHF platelets by RTGG method. After the washing of these platelets with dilute HNO3, pure BaHF powders and platelets were directed by tape casting which was followed by sintering using TGG phenomenon. Degree of achieved texturing in the processed ceramics was studied using Rietveld analysis, pole figure measurement and electron backscattered diffraction (EBSD).
37
Chen, Michael H. "Magnetic phase transitions in praseodymium-barium doped manganites". To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2007. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Lin, Wen-yi. "Barium polytitanate dielectric resonators for microwave wireless communication". Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/19666.
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39
Barry, Nicholas Peter. "Investigations of photorefractive barium titanate at high intensity". Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362353.
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Wilcock, Jennifer Ruth. "Biological minerals formed from strontium and barium sulphates". Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238199.
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41
Ridgway, Leah M. "Magneto-dieletric properties of bismuth substituted barium hexaferrite". Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/12183/.
Testo completoAbstract (sommario):
The work contained within this thesis seeks to address the dielectric and magnetic properties of bismuth substituted barium hexaferrite (composition BaBixFe12-xO19 where x = 0.0, 0.2, 0.5, 0.8, 1.0 and 1.5) across a broad frequency spectrum. This material is potentially of interest in antenna applications (specifically a dielectric resonator antenna) where high permittivity and permeability materials can be exploited to physically minimize the size of antenna devices. At low frequencies (20Hz - 3MHz) LCR meter based analysis was used to investigate the capacitance and inductance of the materials. The highest measured permittivity at 1MHz was Er = 86.18 - 9.910j, tanδ = 0.11. High frequency (45MHz - 20GHz) permittivity was investigated using a vector network analyser (VNA) and coaxial probe. The highest recorded permittivity at 2.45GHz was Er = 14.69 - 1.664j, tanδ = 0:08. A link between substitution level and permittivity and substitution level and inductance was made at either 1MHz or 2.45GHz. The homogeneity of the samples was explored using a near- field permittivity sensor. This showed small localized variations of permittivity across the surface but not significant enough to adversely effect bulk measurements. A dielectric resonator antenna was fabricated using a bismuth substituted barium hexaferrite sample. Resonant frequencies were identified at 6.6, 9.55 and 13.6GHz and radiation patterns for the system showed agreement with published theoretical results. This confirmed the suitability of the material in this application as a high permittivity material with relatively low loss. This thesis contributes to scientific knowledge by characterising a broad range of bismuth composition materials across a wide frequency range, investigating the link between permittivity/inductance and doping level and presenting full results. The material has also been characterised using a near-field permittivity technique and used to fabricated a dielectric resonator antenna which have not previously been undertaken.
42
Goulding, Philip S. "Formation damage arising from barium sulphate scale precipitation". Thesis, Heriot-Watt University, 1987. http://hdl.handle.net/10399/964.
Testo completoAbstract (sommario):
Formation of scale in oilfield pipework has long been a problem. It is also likely that scale might form in the near well-bore region of the reservoir. This thesis examines the simulation of the formation damage possible due to scale, supported by experiments involving mixing brines in sandstone cores. Simulation was performed using a network model to represent the sandstone. The model was "damaged" using precipitation theory and observations on the damage caused to experimental cores. Experiments were performed, using quarried sandstone, to provide data for tuning and matching the model. The experiments used a pressure-tapped core holder to provide more detailed information on the scaling process and a new, two fluid, injection system for better control over mixing of the brines. The experiments demonstrated that permeability loss would be most rapid in the initial stages of scaling. The rate of permeability loss decreased with decreasing supersaturation of the brine mix and Increasing distance from the point of mixing. Characterisation of the permeability decline demonstrated a linear correlation between the damage rate and the initial permeability. Some effects on permeability damage due to morphology of the scale crystals were noted. The crystal morphology was shown to be mainly dependant on the solution composition rather than its supersaturation. Results from the model indicated a great sensitivity to the "poro-perm" characteristics of the network model representing the sandstone. No matching of results to experiments was achieved, but the trends with relation to the permeability change were modelled successfully.
43
Alipanah, Razieh. "Structure development in sol-gel derived barium hexaferrites". Thesis, University of Warwick, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402998.
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Liu, Yang. "Synthesis and Characterisation of Ho-doped Barium Titanate". Thesis, University of Sheffield, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.521852.
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Mavredaki, Eleftheria. "Barium sulphate formation kinetics and inhibition at surfaces". Thesis, University of Leeds, 2009. http://etheses.whiterose.ac.uk/21106/.
Testo completoAbstract (sommario):
This study refers to experimental work and analysis of the barium sulphate deposition onto surfaces. In the oil field the formation of barium sulphate is a major flow assurance issue. The build up of the BaS04 inorganic scale on surfaces and facilities is undesirable as it causes increased function, reduction in production and other flow assurance issues. To date the overwhelming amount of research has been on the bulk precipitation of barite and little attention has been paid to deposition onto surfaces. This study shows an integrated approach to access the formation kinetics of barite at surfaces. Both the formation kinetics and the crystallography of the deposited barite are explored under examined conditions intended to imitate in some part the off-shore environment. In addition the effect of chemical additives performing as inhibitors of the barite growth is kept as a main concern of this study. Understanding the behavior of the inhibitors and their retardation mechanisms can further target the improvement of inhibition and overall antiscaling techniques. The thesis work has demonstrated that the surface growth kinetics of barite is largely different to bulk kinetics and interesting phenomena occur at surfaces especially when inhibitors are used. There are complex interactions of the inhibitor with the scale and both growth kinetics and crystal morphology are affected with threshold concentrations. The input of the inhibition mechanisms is discussed.
46
Skellern, Matthew G. "Structural and electronic properties of barium lanthanum vanadates". Thesis, University of Aberdeen, 2003. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU167989.
Testo completoAbstract (sommario):
A study of the subsolidus region of the BaO-La2O3-V 2O5 phase diagram has been carried out. Four ternary phases can be prepared, one of which has not been previously identified. The four ternary phases are a palmierite solid solution Ba3-3xLa2x V2O8, Ba2LaV3O11, BaLa10V4O26 (new phase) and Ba3La 40V12O93. Addition of BaLa10V 4O26 and the previously omitted phase La1.42V 0.58)3.58 to the ternary system has resulted n a re-determination of the complete phase diagram. A comprehensive study of the Ba3-3xLa 2xV2O8 solid solution has been carried out, employing a number of techniques including x-ray diffraction, infra-red spectroscopy, thermogravemetric analysis, impedance spectroscopy, electron paramagenetic resonance spectroscopy, inductively coupled plasma mass spectroscopy and x-ray absorption near edge structure spectroscopy. Conductivity measurements show the end-member Ba3V2O8 to be an oxide ion conductor, with the conduction mechanism being facilitated by the ease of transformation of the BaO3 layers to BaO2 and vice versa. The La-doped members show an increase in conductivity, with electrons becoming the dominant conducting species. The crystal structure of Ba2LaV 3O11 was confirmed to be isostructural with Ba2BiV 3O11. A full refinement of the structural parameters has been performed. The unit cell is primitive monoclinic, a = 12.44510(3)A, b = 7.78854(12)A, c = 11.26245(21)A and beta = 103.134(4)°, space group P21/c. Preliminary structural studies have begun on the new phase BaLa10V4O26. The x-ray powder pattern has been fully indexed and a possible monoclinic unit cell of a = 20.2939A, b = 5.886A, c = 12.6234A and beta = 118.05° is proposed. The serendipitous synthesis of a barium-deficient celsian phase, Ba0.8A11.6 Si2.4O8, is reported; the structure was solved using Patterson methods. The phase has a monoclinic unit cell with, a = 8.6090(8)A, b = 13.0858(12)A, c = 7.2047(7)A and beta = 115.418(2)°, space group C2/m.
47
Alshoaibi, Adil. "Electrical properties of rare earth-doped barium titanate". Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/17289/.
Testo completoAbstract (sommario):
Samples of undoped BaTiO3, BT were prepared by three mixed oxide routes; hand mixing, HM using a pestle and mortar, ball milling, BM using Y2O3-stabilised zirconia balls and planetary ball milling, PBM using tungsten carbide balls. The electrical properties of slow cooled (SC) and quenched (Q) BT material for HM, BM and PBM samples were studied by impedance spectroscopy, IS after heat treatments in air at different temperatures. IS measurements with application of applied voltage and in atmospheres of different oxygen partial pressure were used to determine the conduction mechanism. The application of bias voltage was used during IS measurements to separate Schottky barrier interfacial impedances from sample impedances. In general, two types of Schottky barrier can be detected: (i) barriers at electrode-sample interfaces due to Fermi level mismatch and (ii) barriers between grains associated with partial oxidation of sample surfaces. In-Ga electrodes were considered to yield ohmic contacts and associated with partial oxidation that also produced the positive temperature coefficient of resistance, PTCR effect. A methodology has been developed to understand the effect of an applied voltage and changing oxygen partial pressure on electrical properties and possible explanations. Rare earth dopants can occupy either Ba or Ti sites or a mixture of Ba and Ti sites depending on their size. This requires charge compensation mechanisms which can be ionic or electronic. The ionic mechanism can involve either cation or oxygen vacancies. A survey has been carried out of the charge compensation mechanism for different rare earth ions (Gd, Dy, Ho, Y, Er and Yb). It was found that Y3+ preferentially occupied the Ti4+ site with charge compensation by oxygen vacancies and therefore, Y behaved as an acceptor with solid solubility limit of ~ 15%. Y3+ can also simultaneously occupy both Ba and Ti sites with a solubility limit of ~ 7.5%, but exclusive occupancy of Ba sites is limited to ~ 1.5%. A partial phase diagram BaO-TiO2-Y2O3 can been presented showing the different solid solutions and the polymorphism of doped BaTiO3. Several parameters affected the electrical properties of pure and doped BT ceramics: the charge compensation mechanism, whether ionic or electronic; the sample preparation methods; the cooling rate at the end of sample heat treatment because many samples lost a small amount of oxygen at high temperature and showed n-type semiconductivity. A common observation was that many slow cooled samples showed weak p-type behaviour attributed to uptake of oxygen on cooling. The holes may be associated with either underbonded oxide (O - ) ions or unavoidable impurities such as Fe3+. Leaky dielectric properties were observed for extrinsic n-type region whereas, normal dielectric properties were observed for extrinsic p-type region. The electrical properties of BaTi1-xYxO3-x/2 samples fired and cooled in air were ferroelectric insulators at x . 0.05 and relaxor ferroelectrics at higher x with no evidence of semiconductivity in any of the samples, whether they were cooled slowly or quenched from high temperatures (1200-1600 .C). The possible occurrence of a resistivity minimum in rare earth doped BT was investigated. Three possible mechanisms for semiconductivity were considered for generating Ti3+ ions: direct donor doping, oxygen loss at high temperatures and a more complex double doping mechanism involving Y3+ and Ti3+ ions to chargebalance the oxygen vacancies. No semiconductivity and resistivity minimum were observed for Yb-BT for all three joins and Er-BT. Semiconductivity was observed for other RE dopants and the total resistivity passed through a minimum at 0.1% RE substitution then increased generally for > 1% Y, Ho, Dy and Gd substitution on all three joins.
48
Chien, Hsin-I. "Microfabrication of barium strontium titanate BaxSr(1-x)TiO3". Thesis, London South Bank University, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.618692.
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Fardin, Ernest Anthony, e efardin@ieee org. "Barium Strontium Titanate Thin Films for Tunable Microwave Applications". RMIT University. Electrical and Computer Engineering, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080104.135507.
Testo completoAbstract (sommario):
There has been unprecedented growth in wireless technologies in recent years; wireless devices such as cellular telephones and wireless local area network (WLAN) transceivers are becoming ubiquitous. It is now common for a single hardware device, such as a cellular telephone, to be capable of multi-band operation. Implementing a dedicated radio frequency (RF) front-end for each frequency band increases the component count and therefore the cost of the device. Consequently, there is now a requirement to design RF and microwave circuits that can be reconfigured to operate at different frequency bands, as opposed to switching between several fixed-frequency circuits. Barium strontium titanate (BST) thin films show great promise for application in reconfigurable microwave circuits. The material has a high dielectric constant which can be controlled by the application of a quasi-static electric field, combined with relatively low losses at microwave frequencies. Tunable microwave components based on BST-thin films have the potential to replace several fixed components, thereby achieving useful size and cost reductions. This thesis is concerned with the growth and microwave circuit applications of BST thin films on c- and r-plane sapphire substrates. Sapphire is an ideal substrate for microwave integrated circuit fabrication due to its low cost and low loss. Electronically tunable capacitors (varactors) were fabricated by patterning interdigital electrode structures on top of the BST films. High capacitance tunabilities of 56% and 64% were achieved for the films grown on c-plane and r-plane sapphire, respectively, at 40 V bias. A novel electronically tunable 3 dB quadrature hybrid circuit was also developed. Prototypes of this circuit were initially implemented using commercial varactor diodes, in order to validate the design. An integrated version of the coupler was then fabricated using BST varactors on c-plane sapphire. The results achieved demonstrate the potential of sapphire-based BST thin films in practical microwave circuits.
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Price, Tony S. "Nonlinear Properties of Nanoscale Barium Strontium Titanate Microwave Varactors". Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4390.
Testo completoAbstract (sommario):
Barium strontium titanate thin film varactors have been widely investigated for the purpose of creating tunable front-ends for RF and microwave systems. There is an abundance of literature observing the capacitance-voltage behavior and methods on improving tunability. However, there is a lack of thorough investigations on the nonlinear behavior, specifically the third order intermodulation distortion, and the parameters that impact it. There is also a research void that needs to be filled for nanoscale barium strontium titanate varactors as nanotechnology becomes increasingly prevalent in the design of RF and microwave components.
This work aims to advance the understanding of nonlinear properties of barium strontium titanate varactors. Temperature and voltage impacts on the third order intermodulation distortion products of BST varactors are observed by two-tone measurements. The material properties of the films are correlated with the nonlinear behavior of the varactors. Additionally, size reduction capabilities are shown by fabricating planar barium strontium titanate interdigital varactors with nanoscale size gaps between the electrodes. Modeling techniques are also investigated.