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1
Mete, Ersen. "Electronic Properties Of Transition Metal Oxides". Phd thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/1069699/index.pdf.
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Transition metal oxides constitute a large class of materials with variety of very interesting properties and important technological utility. A subset with perovskite structure has been the subject matter of the current theoretical investigation with an emphasis on their electronic and structural behavior. An analytical and a computational method are used to calculate physical entities like lattice parameters, bulk moduli, band structures, density of electronic states and charge density distributions for various topologies. Results are
discussed and compared with the available experimental findings.
2
Bogdanov, Nikolay. "Anisotropic interactions in transition metal oxides". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-234886.
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This thesis covers different problems that arise due to crystal and pseudospin anisotropy present in 3d and 5d transition metal oxides. We demonstrate that the methods of computational quantum chemistry can be fruitfully used for quantitative studies of such problems.
In Chapter 2, Chapter 3, and Chapter 7 we show that it is possible to reliably calculate local multiplet splittings fully ab initio, and therefore help to assign peaks in experimental spectra to corresponding electronic states. In a situation of large number of peaks due to low local symmetry such assignment using semi-empirical methods can be very tedious and non-unique.
Moreover, in Chapter 4 we present a computational scheme for calculating intensities as observed in the resonant inelastic X-ray scattering and X-ray absorption experiments. In our scheme highly-excited core-hole states are calculated explicitly taking into account corresponding orbital relaxation and electron polarization. Computed Cu L-edge spectra for the Li2CuO2 compound reproduce all features present in experiment.
Unbiased ab initio calculations allow us to unravel a delicate interplay between the distortion of the local ligand cage around the transition metal ions and the anisotropic electrostatic interactions due to second and farther coordination shells. As shown in Chapter 5 and Chapter 6 this interplay can lead to the counter intuitive multiplet structure, single-ion anisotropy, and magnetic g factors. The effect is quite general and may occur in compounds with large difference between charges of metal ions that form anisotropic environment around the transition metal, like Ir 4+ in plane versus Sr 2+ out of plane in the case of Sr2IrO4.
An important aspect of the presented study is the mapping of the quantum chemistry results onto simpler physical models, namely extended Heisenberg model, providing an ab initio parametrization. In Chapter 5 we employ the effective Hamiltonian technique for extracting parameters of the anisotropic Heisenberg model with single-ion anisotropy in the case of quenched orbital moment and second-order spin-orbit coupling. Calculated strong easy-axis anisotropy of the same order of magnitude as the symmetric exchange is consistent with experimentally-observer all-in/all-out magnetic order.
In Chapter 6 we introduce new flavour of the mapping procedure applicable to systems with first-order spin-orbit coupling, such as 5d 5 iridates based on analysis of the wavefunction and interaction with magnetic field. In Chapter 6 and Chapter 7 we use this new procedure to obtain parameters of the pseudospin anisotropic Heisenberg model. We find large antisymmetric exchange leading to the canted antiferromagnetic state in Sr2IrO4 and nearly ideal one-dimensional Heisenberg behaviour of the CaIrO3, both agree very well with experimental findings.
3
Sadoc, Aymeric Gaël Jocelyn. "Charge disproportionation in transition metal oxides". [S.l. : [Groningen : s.n.] ; University Library Groningen] [Host], 2008. http://irs.ub.rug.nl/ppn/.
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Lau, Bayo. "Modeling polarons in transition-metal oxides". Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/33463.
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This work is a series of reports on progress in the description of electron-electron and electron-lattice interactions in transition-metal oxides, with an emphasis to the class of high-Tc superconducting cuprates. Combinations of numerical and analytical approaches were devised and developed to study large-scale models, which distinguish cation and anion sites of the realistic
lattice structure. The many results range from incremental deviation to significant difference compared to those of the widely-accepted simple models without such distinction. A previously proposed numerical scheme and a perturbation approach were adapted to study the one-dimensional breathing-mode model, which describes a charge carrier interacting with vibrating anions. The effort yielded the first accurate benchmark result for all parameters values of the model. Based on a physical insight about the spin-1/2 Heisenberg antiferromagnet on a two-dimensional square lattice, an octapartite approach was devised to model the low-energy states. The efficiency of the resulting numerical approach was showcased with the explicit solution to a record-breaking 64-spin torus. A spin-polaron model was derived to model holes injected into cuprate's quasi two-dimensional copper-oxygen layer. Total-spin-resolved exact diagonalization was performed for a single fermionic hole in a record-breaking cluster with 32 copper and 64 oxygen sites. The solutions revealed important physics missed by previous studies. The octapartite approach was then developed to solve the spin-polaron model with two extra holes in the same cluster. The accuracy and efficiency of the method were established. Enhanced singlet correlation between two holes was observed. The preliminary results justify the need for an in-depth study.
5
Field, Marianne Alice Louise. "Transition metal oxides and oxide-halides". Thesis, University of Southampton, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401833.
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Guo, Yuzheng. "Electronic structures of transition metal oxides". Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648465.
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Gibbs, Alexandra S. "Emergent states in transition metal oxides". Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3557.
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Transition metal oxides adopt a wide variety of crystal structures and display a diverse range of physical phenomena from Mott insulating states to electron-nematics to unconventional superconductivity. Detailed understanding of these states and how they may be manipulated by structural modifications requires both precise structural knowledge and in-depth physical property measurements using as many techniques over as wide a range of phase space as possible. In the work described in this thesis a range of transition metal oxides were studied using high-resolution powder neutron diffraction and detailed low-temperature physical property measurements. The quaternary barium orthotellurates Ba₂NiTeO₆, Ba₂CuTeO₆ and Ba₂ZnTeO₆ belong to an almost unstudied family of materials. The development of procedures for synthesizing large single crystals has facilitated the investigation of interesting new anisotropic magnetic states in the Cu and Ni systems and the existence of a possible structural phase transition in the Zn-based compound. YMnO₃ is a multiferroic with improper ferrielectricity. The study of the high-temperature structural phases described in this thesis has led to the identification both of the transition path to the ferrielectric state and the identification of an isostructural phase transition within the ferrielectric phase. BiFe₀.₇Mn₀.₃O₃ is also a multiferroic material but with proper ferroelectricity. The investigation of the structural phases of this compound have provided confirmation of the high-temperature phases with the reassignment of the symmetry of the highest-temperature phase which is intriguingly different to that of the unsubstituted material. Finally, an investigation of the electronic structures of the high conductivity delafossites PdCoO₂ and PdCrO₂ using micro-cantilever torque magnetometry measurements of quantum oscillations is described. This has resolved the warping of the Fermi surface of PdCoO₂ and given insights into the complicated Fermi surface of the itinerant antiferromagnet PdCrO₂.
8
Vale, J. G. "The nature of the metal-insulator transition in 5d transition metal oxides". Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/1538695/.
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A number of 5d transition metal oxides (TMOs) either undergo, or lie proximate to, a metal-insulator transition (MIT). However these MITs frequently depart from a Mott-Hubbard picture, in which the interactions are dominated by the interplay between the on-site Coulomb repulsion and electronic bandwidth. In 5d TMOs the sizeable intrinsic spin-orbit coupling plays an important role, and gives rise to electronic and magnetic ground states -- at both sides of the MIT -- that cannot be adequately described within a purely L-S coupling scenario. In this thesis the aim is to understand the role of spin-orbit coupling in determining the electronic and magnetic properties of 5d TMOs. There has been a large amount of recent interest within this field (both experimentally and theoretically), however thus far has mostly been limited to the 5d5, j =1/2 limit. The perovskite iridates Sr2IrO4 and Sr3Ir2O7 lie within this limit. Theoretical predictions suggest a significant easy-plane anisotropy is present for the single layer Sr2IrO4. I show that this anisotropy can be observed and quantified, using magnetic critical scattering and previously published resonant inelastic X-ray scattering (RIXS) data. This differs from previous results that suggest purely 2D Heisenberg behaviour. Meanwhile the critical fluctuations in bilayer Sr3Ir2O7 have a three-dimensional nature, which can be directly related to the intra-bilayer coupling and significant anisotropy previously probed by RIXS. I also demonstrate that resonant X-ray scattering techniques can be successfully applied to other 5d systems, especially the d3 osmates. Both NaOsO3 and Cd2Os2O7 undergo MITs directly linked to the onset of antiferromagnetic order (Slater or Lifshitz mechanisms). The first ever high-resolution RIXS measurements at the Os L3 absorption edge reveal that there is a correlated evolution of the electronic and magnetic excitations through the respective MITs. The behaviour is consistent with a scenario in which the effect of spin-orbit coupling and electron correlations are reduced with respect to the iridates, yet still manifests through a strong spin wave anisotropy. Finally I show that the study of 5d TMOs can be extended into the time domain. Through the development of new instrumentation, the transient dynamics of photo-doped Sr2IrO4 were probed by time-resolved resonant (in)elastic X-ray scattering. The relevant time scales can be directly compared to the interaction strengths and anisotropies in the undoped state. Moreover, there seems to be an effective mapping of the transient behaviour in the photo-doped state to an equivalent level of bulk electron doping in (Sr_{1-x}La_x)2IrO4.
9
Mann, Peter David Alexander. "Electronic structure of layered transition metal oxides". Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612888.
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McAllister, Judith Ann. "Lattice effects in layered transition metal oxides". Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621529.
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Hickey, Peter James. "Structural studies of layered transition metal oxides". Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/173977/.
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A number of transition metal oxide materials, both new and previously reported, have been synthesised, their structures based on the n = 2 Ruddlesden-Popper layered perovskites. Their structures were determined through Rietveld refinement against X-ray and neutron powder diffraction, supported by vibrating sample magnetometry and thermal analysis. The structure of the double layered phase Gd2SrCo2O7 was determined in the temperature range 300 – 973 K by refinement of powder neutron diffraction data. The room temperature structure is tetragonal, and displays small tilts of the oxygen sublattice that are described by a 2a0 2a0 x c supercell model in the space group P42/mnm rather than the idealised Sr3Ti2O7 I4/mmm structure as previously reported. A structural transition at ~ 580 K is characterised by reduction in the unit cell symmetry and distortion of CoO6 octahedra; the behaviour is concurrent with a spin crossover in the Co (III) ions from intermediate to high spin. The structure of the new phase Nd2BaCo2O7 was determined in the temperature range 298 – 873 K by refinement of powder neutron diffraction data. At all temperatures, the structure is metrically tetragonal, however the octahedral rotations are best described in the orthorhombic space group Bbcb, with a = b = 2a0. The structures of the phases Ln2SrFe2O7 (Ln = La, Nd, Gd) have been determined by refinement of variable temperature powder neutron diffraction data. At room temperature all the materials crystallise in the tetragonal space group P42/mnm, isostructural with the phase Tb2BaFe2O7. On heating, the gadolinium and neodymium phases undergo transitions to lower symmetry; the octahedral tilts of the high temperature phases are best described in the space group Bbmm. The new phases Nd2-xSr1+xFe2-xO7 have been prepared and their structures determined by Rietveld refinement of room temperature powder neutron diffraction. All the materials crystallise in the tetragonal space group P42/mnm. The degree of octahedral tilting decreases as x increases, indicating a reduction of compression of the perovskite lattice as the average A-site cationic radius increases. The phase Sr3CoNbO7 has been prepared and its structure determined by refinement of powder neutron diffraction data. At room temperature and 3.4 K there is no evidence of magnetic ordering, B-site cationic ordering or octahedral tilting. The material is isostructural with the undistorted Sr3Ti2O7, which implies that the spin state of Co (III) in the material is low spin. The material Sr3Ti2O7 was prepared and its structure determined in the temperature range 298 – 1073 K. At all temperatures, the structure is tetragonal, with no rotations of octahedra. Unit cell parameters and bond lengths expand smoothly over the temperature range.
12
Gummow, Rosalind June. "Lithium intercalation reactions with transition metal oxides". Doctoral thesis, University of Cape Town, 1993. http://hdl.handle.net/11427/19039.
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An investigation of several lithium transition metal oxide systems has been undertaken with the aim of synthesising an optimised LiM0₂ compound (M = Mn, Co or Co/Ni mixtures) for application as a cathode in rechargeab1e lithium batteries. Attention has been focused on systems which show promise for application as cathodes in rocking-chair cells which do not contain metallic lithium anodes. A novel lithium cobalt oxide, LT-LiCoO₂ (LT for low temperature), has been synthesised at 400°C. This compound has near-cubic symmetry and can be indexed to either a trigonal unit cell (space group R3m) with a=2.830(1)Å and c=l3.875(8) Å, or to a face-centred cubic unit cell (space group Fd3m) with a=8.002(1)A. The near-cubic symmetry is maintained on delithiation. Neutron and X-ray powder diffraction refinement of the LT-LiCoO₂ sample has shown it to be best described as a layered structure (R3m symmetry) with approximately 6% of the cobalt cations in the predominantly lithium layer and vice versa. An acid-leached sample LT-Liₒ₄.4CoO₂ was, however, shown to have a defect spinel structure.
13
De, Silva Theja Nilantha. "Spin-Orbital Physics in Transition Metal Oxides". University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1092948911.
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14
Adem, Umut. "Magnetodielectric coupling in multiferroic transition metal oxides". [S.l. : [Groningen : s.n.] ; University of Groningen] [Host], 2008. http://irs.ub.rug.nl/ppn/.
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Simpson, Jeffrey Ray. "Optical properties of strongly correlated transition metal oxides". College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/2079.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2004.Thesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
16
Payne, David J. "The Electronic Structure of Post Transition Metal Oxides". Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491678.
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The electronic structure of the oxides Pb02, In203, PbO and Bh03 have been studied using high resolution X-ray photoelectron spectroscopy (XPS), ultra-violet photoemission spectroscopy (UPS), hard X-ray photoelectron spectroscopy (HXPS), and X-ray emission (XES). These techniques are supported by band structure calculations carried out within the framework of density functional theory (DFT). It has been demonstrated using UPS, XPS and HXPS that the metallic nature l Trinity Term 2008. David J. Payne Submitted for the degree of Doctor of Philosophy Trinity College, Oxford. ,. ~!II ItI \IfI [l I ofPb02 arises from the occupation of conduction band states above the Fermi level of stoichiometric Pb02, most likely arising from oxygen vacancy defects. XPS and HXPS studies of the Pb 4/ core line show that strong satellites are observed at an energy consistent with the plasmon frequency observed in electron energy loss spectra. These satellites are not present in UPS measurements of the Pb 5d core line. It has been shown using XPS, HXPS, XES and DFT that the fundamental band gap for In203 is much smaller than the often quoted value of 3.75 eV. The fundamental band gap is direct, but direct optical transitions give minimal intensity until 0.81 eV below the valence band maximum. The results are consistent with a fundamental bandgap in the region of2.67eV. Structural distortions in post-transition metal oxides are often explained in terms of the influence of sp hybrid 'lone pairs'. XPS and XES measurements on a- PbO and a-Bh03 show that this model must be revised. A high density of metal 6s states is observed at the bottom of the valence band, and would therefore be unable to directly participate in hybridization with metal 6p states which lie above the valence band. These measurements are consistent with the results of density functional theory calculations.
17
Abdoullah, Mohamad. "Supported transition metal oxides as solid base catalysts". Thesis, University of Huddersfield, 2016. http://eprints.hud.ac.uk/id/eprint/28325/.
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The initial objective of the work studied here was to investigate the effects of isomorphously-substituted transition metals in lattice sites in Layered Double Hydroxides (LDHs) in terms of basicity and catalytic activity in base-catalysed reactions and oxidation reactions. Experiments in which copper(II), nickel(II), cobalt(II), zinc(II) and iron(III) were substituted in the lattice of synthetic hydrotalcites showed that, on calcination, the resultant mixed oxides arising from hydrotalcites containing copper(II) exhibited the greatest enhancement of catalytic activity. Test reactions were the conversion of 4-methylpentan-2-ol to methylisobutylketone, the oxidation of benzyl alcohol and the Henry reaction between benzaldehyde and nitromethane. Results showed conclusively that copper(II) imparted base catalytic activity to the mixed metal oxides formed on calcination of the LDHs. This was confirmed through an extension to the study in which the copper(II) content in the LDHs was varied. It was shown that there is an optimum copper(II) loading, above which additional copper(II) is not effectively incorporated in the LDH lattice. Other supports for copper(II) as an oxide were investigated, on the basis that activity was linked to effective dispersion of copper(II) oxide. A series of copper(II) dispersions on zirconia, on silica and on magnesium oxide were prepared and tested. The zirconia-supported catalysts were the most active so work was concentrated on these. Two methods for preparing copper(II) oxide/zirconia were investigated, using a solid state reaction and using a sol-gel process. Catalysts were prepared with molar copper contents of from 2 to 60 mol%. It was possible to see from powder X-ray diffraction that copper(II) was dispersed in the zirconia matrix at levels up to about 20% depending on the synthetic method. And it was shown that base-catalytic activity of these materials correlated with the amount of fully incorporated copper(II). Activities of these were generally higher than the mixed metal oxides made from the LDHs. For comparison, another, different, approach to incorporating basicity in oxide supports was examined, in which alkylamino groups were tethered to silica supports, specifically a mesoporous molecular sieve form of silica, SBA-15. The activity of these materials were compared with those of the copper(II) based catalysts in the Henry reaction between nitromethane and benzaldehyde. An advantage of these catalysts was exploited by coordinating palladium(II) to the amine groups at different levels to impart oxidation catalytic activity. The resultant materials, in which only part of the amine functionality was coordinated by palladium(II), were tested as bifunctional catalysts, for combined oxidation and base catalytic activity, in the two step reaction between benzyl alcohol and nitromethane, which proceeds via an oxidation step to benzaldehyde followed by a base-catalysed step. The overall conclusion was that copper(II) is effective at imparting base catalytic activity to a range of support oxides, and that it does not have significant activity towards oxidation reactions., contrary to some claims in the literature. Oxidation activity can be obtained alongside base activity by preparing bifunctional catalysts but only through a different approach.
18
Millburn, Julie Elizabeth. "Structural and electronic properties of transition metal oxides". Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364166.
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Wilkins, Stuart Brian. "Charge and spin correlations in transition metal oxides". Thesis, Durham University, 2002. http://etheses.dur.ac.uk/4101/.
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Strongly correlated electron systems such as the transition metal oxides have provided important results in condensed matter physics over the past few years. They display intriguing phenomena such as superconductivity, colossal magnetoresistance and stripe ordering due to charge and spin correlations at low temperatures. This thesis presents the study of hole doped nickelate and manganite materials using X-ray scattering over an extended energy range. The development of X-ray scattering at energies ranging from 600 eV up to 130 keV is reported. High energy scattering results, are presented on the La(_2-x)Sr(_x)NiO(_4+6) system with x = 0.33. The sensitivity of X-ray scattering to the charge distribution combined with the use of high energy X-rays has allowed the bulk of the sample to be probed, and have resulted in the discovery of a 'charge stripe glass' within the bulk of the material. We compare these results to previous measurements in the near surface region using ~ 12 keV X-rays. Jahn - Teller, charge and orbital ordering has been studied in the Bi(_1-x)Ca(_x)MnO(_3) system with x = 0.74 and the bilayer manganite La(_2-2x)Sr(_1+2x)Mn(_2)O(_7) with x = 0.475 using resonant X-ray scattering techniques at the manganese K edge and high energy X-ray scattering. These results have confirmed the wavevector of ordering along with their associated correlations. The design, and commissioning of a novel diffractometer using focused X-rays from graded & spacing parabolic mirrors is presented. Results show an increase of 10 fold in intensity, together with a simultaneous increase in resolution of 7.5 over previous systems employing graphite monochromating crystals. The first single-crystal X-ray diffraction results are presented which display huge resonances at the L edges of manganese. The resonant enhancement is sufficiently large to allow the observation of magnetic scattering from a correlated antiferromagnetic alignment of spins. Resonant soft X-ray scattering will become a important technique for the study of 3d magnetic materials in the future such as the superconducting, striped cuprate systems.
20
Leonov, Ivan [Verfasser]. "Charge Order in Transition Metal Oxides / Ivan Leonov". Aachen : Shaker, 2007. http://d-nb.info/116434093X/34.
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Nicoll, Steven. "Simulation studies of transition metal and actinide oxides". Thesis, University College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308937.
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Wright, Jonathan Paul. "Powder diffraction studies of frustrated transition metal oxides". Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620972.
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Patino, Midori Amano. "Topochemical manipulation of some complex transition metal oxides". Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:e312bf34-98d5-4818-bb50-fd8772688a1d.
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This thesis is comprised of three parts. The first part concerns the investigation of the topochemical reduction of LaSrNiRuO6 in order to prepare LaSrNiRuO4 via anion deintercalation. The second part discusses the oxide-for-hydride anion exchanges performed in SrV1-xTixO3, and the resulting SrV1-xTixO2-yH1+y reduction products. Finally, the results from redox-neutral topochemical cation exchange reactions conducted in the three-dimensional perovskite structure of NaTaO3 are presented along with the characterisation of a novel product of composition Ni0.5TaO3. The topochemical reduction of LaSrNiRuO6 using CaH2 was carried out to produce a novel extended oxide phase with composition LaSrNiRuO4. This phase is composed of sheets of apex-linked Ni1+O4 and Ru2+O4 squares in a checkerboard ordered arrangement. To the best of our knowledge, this material is the first example of a B-cation ordered infinite-layer oxide phase. The low oxidation states of the transition-metal cations are confirmed by DFT calculations from which a spin moment S = ½ is determined for the nickel while the ruthenium centres adopt an intermediate-spin S = 1 configuration. LaSrNiRuO4 behaves paramagnetically at room temperature. However, upon cooling (T < 250 K) a phase transition is observed in which the nickel spins interact ferromagnetically, while the ruthenium cations appear to undergo a change in spin configuration to a diamagnetic spin state. A possible explanation is given for this observation based on an ordered arrangement of local Jahn-Teller distortions. While investigating the preparation of LaSrNiRuO4, it was observed that different samples of the LaSrNiRuO6 starting materials exhibited markedly different reactivity. The observed differing reactivity is inconsistent with the crystal structure and composition of the LaSrNiRuO6 samples, from which all the materials are identical. Careful investigation of the X-ray diffraction data collected from the LaSrNiRuO6 materials revealed that the reactivity of the samples is a consequence of the microstructure. By quenching or slow-cooling the materials during their synthesis, the size of the crystalline domains formed is affected and this in turn is observed to define the extent to which the topochemical deintercalation of oxide anions takes place. A mechanism to explain this effect is presented in which the greater 'plasticity' of small crystalline domains helps to limit the influence of lattice strain during the reaction. Similar with the observations for the LaSrNiRuO6 phases, it was found that the reactivity of SrV0.95Ti0.05O3 samples towards topochemical oxide-for-hydride exchange is also determined by the characteristics of the starting materials. The cooling rate can lead to phase segregation in SrV0.95Ti0.05O3 samples which in turn affects the reduction behaviour. A modification of the energy profile for the oxide-for-hydride exchange in SrV1-xTixO3 phases is proposed on the basis of the electronic configuration that the transition-metal cations adopt upon reduction (d2,V3+ and d1,Ti3+). Finally, topochemical exchange reactions can also be carried out between cations in complex transition metal oxides when the mobility of the species to be exchanged is sufficiently greater with respect to the host lattice. The preparation of Ni0.5TaO3 from exchange of Na+ by Ni2+ in NaTaO3 represents a synthetic approach not yet widely explored in the long-standing challenge that the preparation of magnetoelectric multiferroic materials represents. The topochemical reactions studied in this work highlight the possibility of directing and modifying the product phases, by tuning features of the reagents. This is in contrast with the limited control available in thermodynamic processes.
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Şahin, Aytaç Eanes Mehtap. "Hydrothermal Synthesis and Characterization of Transition Metal Oxides/". [s.l.]: [s.n.], 2004. http://library.iyte.edu.tr/tezler/master/malzemebilimivemuh/T000435.doc.
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Hallam, Keith Richard. "Carbon deposition on transition metal- and uranium-oxides". Thesis, Open University, 1991. http://oro.open.ac.uk/57324/.
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Advanced gas cooled nuclear reactors (AGRs) contain a range of alloys, selected for their physical and chemical performance in the conditions present. Carbon deposition on boiler and fuel pin heat transfer surfaces affects a reactor's efficiency and may necessitate downrating to maintain safety margins. This is believed to arise from decomposition of some of the coolant gas constituents. Deposition minimisation, while maintaining the structural integrity of the reactor, is technologically and economically important. This study has looked at deposition on a range of transition metal spinels, manganese oxides, uranium oxides and single crystal magnetite samples with a view to furthering knowledge of catalytic reactions that may occur within an AGR. In particular, the effect of mixed valency on deposition rates was studied. The spinels were successfully prepared by solid state reactions between the relevant oxides, oxalates and I or carbonates. A range of elemental and chemical analytical techniques were used to characterise the samples both before and after exposure under controlled gas and radiological conditions. Deposition was induced, to varying extents, on all the samples exposed. No filamentary deposits were observed. The spinels gave quantities of deposition in the order: Manganese spinels gave increasing deposition with increasing manganese content at 650°C, but decreasing deposition at 550°C. Iron-cobalt spinels showed no consistent increase or decrease in carbon deposition with changing composition. Nickel rich spinels were unstable in the reaction gas mixture and generated metallic nickel during exposure. At both temperatures, this gave levels of carbon deposition which increased with increasing nickel content of the original oxide. NiF~04 exposed at 550°C fragmented as it catalysed carbon formation. Manganese oxides converted to MnO during exposure, MnO proving also to be a most effective catalyst. Mn304' an Mn2+ I Mn3+ compound where the manganese ions do not form an electron exchanging octahedrally coordinated pair, did not yield large quantities of deposit. The uranium oxides examined converted to the interacting mixed valence U409' which gave copious carbon deposition. The U4+ I U6+ non interacting mixed valence Ot-U30 S gave the least deposition. Magnetite slices gave laminar carbon deposits, but no filamentary growth. Structured deposit was seen in two cases, including on one face oriented approximately parallel to the [111] plane, the plane previously expected to catalyse deposition most effectively.
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Smith, Adam. "Transition Metal Oxides for Solar Water Splitting Devices". Thesis, University of Oregon, 2016. http://hdl.handle.net/1794/19670.
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Although the terrestrial flux of solar energy is enough to support human endeavors, storage of solar energy remains a significant challenge to large-scale implementation of solar energy production. One route to energy storage involves the capture and conversion of sunlight to chemical species such as molecular hydrogen and oxygen via water splitting devices. The oxygen evolution half-reaction particularly suffers from large kinetic overpotentials. Additionally, a photoactive material that exhibits stability in oxidizing conditions present during oxygen evolution represents a unique challenge for devices. These concerns can be potentially addressed with a metal oxide photoanode coupled with efficient water oxidation electrocatalysts. Despite decades of research, structure-composition to property relationships are still needed for the design of metal oxide oxygen evolution materials.
This dissertation investigates transition metal oxide materials for the oxygen evolution portion of water splitting devices. Chapter I introduces key challenges for solar driven water splitting. Chapter II elucidates the growth mechanism of tungsten oxide (WOX) nanowires (NWs), a proposed photoanode material for water splitting. Key findings include (1) a planar defect-driven pseudo-one-dimensional growth mechanism and (2) morphological control through the supersaturation of vapor precursors. Result 1 is significant as it illustrates that common vapor-phase syntheses of WOX NWs depend on the formation of planar defects through NWs, which necessitates reconsideration of WOX as a photoanode. Chapter III presents work towards (1) single crystal WOX synthesis and characterization and (2) WOX NW device fabrication. Chapter IV makes use of the key result that WOX NWs are defect rich and therefore conductive in order to utilize them as a catalyst scaffold for oxygen evolution in acidic media. Work towards utilizing NW scaffolds include key results such as stability under anodic potentials and strongly acidic conditions used for oxygen evolution. Chapter V includes work characterizing nickel oxide/oxyhydroxide oxygen evolution catalysts at near-neutral pH. Key findings include (1) previous reports of anodic conditioning resulting in greater catalytic activity are actually due to incidental incorporation of iron impurities from solution and (2) through intentional iron incorporation via electrochemical co-deposition, catalytic activity is increased ~50-fold over Fe-free catalysts.
This dissertation contains previously published coauthored material.
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Teran, Escobar Gerardo. "Solution-Processed Transition Metal Oxides for Organic Solar Cells". Doctoral thesis, Universitat Autònoma de Barcelona, 2013. http://hdl.handle.net/10803/131406.
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Las celdas solares orgánicas se han convertido en una promesa para la producción de energía a bajo costo, y su potencial se refleja en los enormes esfuerzos para mejorar su eficiencia. En los últimos 30 años, esta tecnología ha crecido enormemente, con prototipos de laboratorio mostrando eficiencia mayor que 10 % . El continuo desarrollo de polímeros semiconductores, materiales de amortiguamiento, y el conocimiento profundo sobre el intercambio electrónico en las interfaces, han sido las principales razones de este crecimiento.
Sin embargo, la mejora de esta tecnología a estados de producción de bajo coste como tecnologías de impresión R2R es el objetivo, y el desarrollo de materiales de procesamiento de baja temperatura es el reto a superar.
En este trabajo, se ha explorado en profundidad la aplicación de los óxidos de metales de transición como capas tampón electrónicos como TiO2 , ZnO como capas de transporte de electrones , y V2O5 , NiO como capas de transporte de huecos. También muestra el desarrollo de una tinta base agua con procesamiento a baja temperatura de V2O5 para aplicaciones R2R, así como la aplicación de película de NiO sinterizado a baja temperatura (350oC) y la caracterización mediante diferentes técnicas espectroscópicas.
Además se muestran los estudios de estabilidad a largo plazo, como en interiores y al aire libre, la realización de estudios de degradación de los diferentes dispositivos desarrollados.Organic Solar Cells (OSCs) have emerged as a promise for low cost energy production, and its potential is reflected in the huge efforts to improve their efficiencies. In the last 30 years, this technology has grown enormously; nowadays the state of the art is showing efficiencies higher than 10%. The continuous development of semiconducting polymers, buffer materials, and the depth knowledge about the electronic exchange at the interfaces, have been the principal reasons of this growing. Nevertheless, upgrading this technology to low cost production states like roll to roll printing technologies is the goal, and the development of low temperature processing materials is the challenge to overcome. In this work, it has explored in depth the application of Transition Metal Oxides (TMOs) as electronic buffer layers like TiO2, ZnO as electron transport layers, and V2O5, NiO as hole transport layers. Also shows the development of a water base low temperature solution-processed V2O5 ink for R2R applications, as well as the application of NiO film sintered at low temperature (350oC) and the characterization by distinct techniques. As well, the long-term stability studies, like indoor and outdoor; carrying out degradation studies for the different architecture devices tested.
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Popa, Andreia Ioana. "Electrochemistry and magnetism of lithium doped transition metal oxides". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-26029.
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The physics of transition metal oxides is controlled by the combination and competition of several degrees of freedom, in particular the charge, the spin and the orbital state of the electrons. One important parameter responsible for the physical properties is the density of charge carriers which determines the oxidization state of the transition metal ions. The central objective in this work is the study of transition metal oxides in which the charge carrier density is adjusted and controlled via lithium intercalation/deintercalation using electrochemical methods. Lithium exchange can be achieved with a high degree of accuracy by electrochemical methods. The magnetic properties of various intermediate compounds are studied.
Among the materials under study the mixed valent vanadium-oxide multiwall nanotubes represent a potentially technologically relevant material for lithium-ion batteries. Upon electron doping of VOx-NTs, the data confirm a higher number of magnetic V4+ sites. Interestingly, room temperature ferromagnetism evolves after electrochemical intercalation of Li, making VOx-NTs a novel type of self-assembled nanoscaled ferromagnets. The high temperature ferromagnetism was attributed to formation of nanosize interacting ferromagnetic spin clusters around the intercalated Li ions. This behavior was established by a complex experimental study with three different local spin probe techniques, namely, electron spin resonance (ESR), nuclear magnetic resonance (NMR) and muon spin relaxation spectroscopies.
Sr2CuO2Br2 was another compound studied in this work. The material exhibits CuO4 layers isostructural to the hole-doped high-Tc superconductor La2-xSr2CuO4. Electron doping is realized by Li-intercalation and superconductivity was found below 9K. Electrochemical treatment hence allows the possibility of studying the electronic phase diagram of LixSr2CuO2Br2, a new electron doped superconductor. The effect of electrochemical lithium doping on the magnetic properties was also studied in tunnel-like alpha-MnO2 nanostructures. Upon lithium intercalation, Mn4+ present in alpha-MnO2 will be reduced to Mn3+, resulting in a Mn mixed valency in this compound. The mixed valency and different possible interactions arising between magnetic spins give a complexity to the magnetic properties of doped alpha-MnO2.
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Kimber, Simon A. J. "Spin and orbital ordering in ternary transition metal oxides". Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/3487.
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Spin and orbital orderings are amongst the most important phenomena in the solid state chemistry of oxides. Physical property and powder neutron and X-ray diffraction measurements are reported for a range of mostly low dimensional ternary transition metal oxides which display spin or orbital order. Extensive studies of the physical properties and crystal structure of In2VO5 are reported. The structure of this material consists of one dimensional zig-zag chains of orbitally ordered S = 1/2 V4+. Magnetic susceptibility measurements show an unusual crossover from dominant ferromagnetic (θ = 17 K) to antiferromagnetic (θ = -70 K) exchange at 120 K, which is attributed to ferromagnetic dimerisation driven by magnetic frustration. The magnetic moment also increases from 1.81 to 2.2μB at the 120 K crossover. Heat capacity measurements confirm this scenario as the magnetic entropy tends towards 1/2 Rln3 below 120 K before approximating to Rln2 at high temperature. Synchrotron x-ray diffraction and high resolution neutron powder diffraction show no bulk structural changes, but the b axis, along which the VO6 chains run, shows an anomalous expansion below 120 K. At low temperatures, a downturn in the magnetic susceptibility is seen at 2.5 K, signifying a spin freezing transition. Heat capacity and powder neutron diffraction measurements show no evidence for long range magnetic order down to 0.42 K. The low dimensional brannerite materials MV2O6 (M = Mn, Co, Ni) were synthesised by a sol-gel method. Magnetic properties were investigated by magnetisation, powder neutron diffraction and in the case of CoV2O6, heat capacity measurements. The structure of these materials consists of linear chains of edge sharing MO6 octahedra. Monoclinic MnV2O6 is an isotropic antiferromagnet with TN = 20 K and a reduced magnetic coherence length due to 3 % Mn/V antisite disorder. The magnetic structure consists of ferromagnetic edge-sharing chains with k = (0,0,1/2) and a refined Mn moment of 4.77(7) μB. The triclinic materials CoV2O6 and NiV2O6 are also antiferromagnetic with TN = 7 and 14 K respectively and both show metamagnetic type transitions. Unusually, M(H) isotherms recorded below 5 K for CoV2O6 show a plateau at 1/3 of the saturation magnetisation. This feature, together with a long period modulated magnetic structure, is attributed to strong single ion (Ising) type anisotropy and nearest neighbour ferromagnetic exchange. Preliminary high pressure experiments on NiV2O6 have confirmed a previously reported transition to a columbite phase at 6 GPa and 900 °C. The high pressure polymorph is also antiferromagnetic with TN = 2.5 K. The previously uncharacterised perovskite, PbRuO3 has been prepared using high pressure/temperature synthesis techniques (10 GPa, 1000 °C). Synchrotron powder X-ray diffraction measurements show that the room temperature structure is orthorhombic, Pnma. A first order orbital ordering transition occurs at 75 K with an associated metal insulator transition. Below 75 K, the dxz orbitals are preferentially occupied and the structure is orthorhombic Imma. The transition may be driven by an increase in antiferroelectric Pb2+ displacements, whcih reach a peak at ~ 125 K. A further structural transition to a larger monoclinic cell is also identified at 9.7 K. The physical properties and crystal structures of two low dimensional lead manganese oxides have also been investigated. Acentric Pb2MnO4, which has a structure consisting of edge sharing chains, is antiferromagnetic with TN = 18 K. Powder neutron diffraction shows the magnetic structure consists of antiferromagnetic chains with k = (0,0,0) and a refined Mn moment of 2.74(2) μB. The crystal point group allows piezoelectricity and the magnetic point group symmetry allows piezomagnetism. We speculate that coupled magnetic and electric properties may be observed in this material. The layered material, Pb3Mn7O15, with a structure consisting of 1/2 filled Kagomé layers has also been studied. Single crystals were prepared by a flux growth method and polycrystalline material was prepared by the ceramic method. Powder neutron and synchrotron x-ray diffraction studies show that the single crystals are hexagonal and that the polycrystalline material is orthorhombic. Furthermore, heat capacity measurements show that the hexagonal single crystal material undergoes a glassy magnetic transition. In contrast, powder neutron diffraction shows that the orthorhombic polycrystalline material has coherent long range magnetic order. These differences are attributed to an oxygen deficiency in the polycrystalline magnetic order. These differences are attributed to an oxygen deficiency in the polycrystalline material.
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Krimmel, Alexander [Verfasser]. "Electronically highly correlated ternary transition metal oxides / Alexander Krimmel". Hamburg : Diplom.de, 2005. http://d-nb.info/1179775953/34.
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Senn, Mark Stephen. "Charge, orbital and magnetic ordering in transition metal oxides". Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7828.
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Neutron and x-ray diffraction has been used to study charge, orbital and magnetic ordering in some transition metal oxides. The long standing controversy regarding the nature of the ground state (Verwey structure) of the canonical charge ordered material magnetite (Fe3O4) has been resolved by x-ray single crystal diffraction studies on an almost single domain sample at 90 K. The Verwey structure is confirmed to have Cc symmetry with 56 unique sites in the asymmetric unit. Charge ordering is shown to be a useful first approximation to describe the nature of the ground state, and the conjecture that Verwey made in 1939 has finally been confirmed. However, three-site distortions which couple to the orbital ordering of the Fe2+ ordered states (trimerons) are shown to provide a more complete description of the low temperature structure. Trimerons explain the rather continuous distribution of the valence states observed in magnetite below Tv, anomalous shortening of Fe-Fe distances and the off-centre distortions resulting in ferroelectricity. DFT+U electronic structure calculations on the experimental coordinates support the conclusion of this crystallographic study, with the highest electron densities calculated for those Fe-Fe distances predicated to participate in the trimeron bonds. The 6H-perovskites of the type Ba3ARu2O9 have been reinvestigated by high resolution neutron and x-ray power diffraction. The charge ordered state of Ba3NaRu2O9 has been characterised at 110 K (P2/c, a =5.84001(2) Å, b = 10.22197(4) Å, c = 14.48497(6) Å, β = 90.2627(3) °) and shown to consist of a structure with near integer charge ordering of Ru5+ 2O9 / Ru6+ 2O9 dimers. The ground state has been shown to be very sensitive to external perturbations, with a novel melting of charge ordering observed under x-ray irradiation below 40 K (C2/c, a =5.84470(2) Å, b = 10.17706(3) Å, c = 14.45866(5) Å, β = 90.2151(3)-° at 10 K). High pressure studies reveal that the Ru-Ru intra-dimer distance may dictate the response of the system to pressure. Empirical trends in the Ba3ARu2O9 series of compounds have shown that change in ‘chemical pressure’ in these systems may be rationalised in terms of Coulomb’s law. In A = La and Y the magnetic ordering is shown to be FM within the Ru2O9 dimers (1.4(2) μB and 0.5(1) μB, respectively per Ru), representing the first case of intra dimer FM coupling reported in a system containing face-sharing RuO6 octahedra . The overall AFM coupling of the dimers implies an as yet unobserved breaking of the parent symmetry. In A = Nd, a complex competition between the crystal field effect of Nd3+ and the magnetic ordering of the Ru2O9 FM moments has been observed, leading first vi to FM order of Nd at 25 K (1.56(7) μB) followed by ordering of Ru moments (0.5(1) μB) and a spin reorientation transition of Nd moments at 18 K. In A = Ca, the formation of a singlet ground state is observed in Ru2O9 rather than the expected AFM coupling and below 100 K Ba3CaRu2O9 is diamagnetic. All five systems indicate that the Ru2O9 dimer is the physically significant unit in these systems when considering structural trends and the ordering of charge, spin and orbital degrees of freedom.
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Hunter, Ross. "Transition metal oxides and dust in extended stellar atmospheres". Thesis, University of Nottingham, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416415.
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Adomkevicius, A. "Controlling transition metal oxides nanostructures for energy storage systems". Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3007846/.
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This thesis focuses on several approaches for the development of high charge/discharge rate lithium-ion batteries and electrochemical capacitors. The general background of lithium-ion batteries and electrochemical capacitors, and experimental techniques and methods are presented in the Chapter 1 and Chapter 2. The Chapter 3 in this thesis discusses the development of nanostructured cathodes for lithium-ion battery by introducing graphene or base washed graphene oxide as conductive additive. The carbon black is the most used conductivity enhancing additive in today’s lithium-ion batteries, nevertheless, makes it difficult for carbon black particles to form a wide-ranging “point-to-point” conductive network. Essentially, higher amounts of carbon black should be added in the electrodes to achieve percolation, leading to a lowering of the gravimetric capacity of the battery. Chapter 3 will detail the conditions used to investigate the optimal electrode composition containing different ratios and particle sizes of intercalation material and conductive additives (graphene and carbon black) in order to improve connectivity and conductivity leading to superior performance of a lithium-ion cathode material, Li(Ni1/3Mn1/3Co1/3)O2 at high charge/discharge rates. The second part of this work is focuses on electrochemical capacitors based on transition metal oxide. Manganese oxide (MnO2) is recognised as promising pseudocapacitive material, however poor ionic and electronic conductivity is the major limiting factor for its practical application. Chapter 4 discuss that through a straightforward and scalable synthesis it is possible to develop a bulk MnO2 material with randomly isolated layers. The synthesis conditions promote the formation of disordered material that allow ion transfer throughout the material that is not limited by solid state diffusion. Relatively low temperatures and inclusion of Na+ disrupt the formation of a highly crystalline material with a large domains size leading to a capacitance of ~200 F g-1 which was maintained at extremely high rates (1000 mV s-1 and 200 A g-1) for disordered Na0.35MnO2 nanosheets. In Chapter 5, an aqueous asymmetric electrochemical capacitor was assembled with Na0.35MnO2 pseudocapacitive electrode material as the positive electrode and activated carbon (AC) as the negative electrode. The optimisation charge balance between positive and negative electrodes, and modification of 0.5 M Na2SO4 aqueous electrolyte with addition of small amount of NaHCO3, is possible to suppress manganese oxide dissolution and hydrogen evolution, leading to long-term cycling at extended cell voltage of 2.4 V. In Chapter 6 following the promising results with Na0.35MnO2 within Chapter 4, other alkali metal intercalated MnO2 were investigated. Results show that the inclusion of the larger non-hydrated K+ (ionic radius = 1.52 Å) is key in the phase-controlled synthesis, where alkaline ion can serve as a template in the formation of layered structures of MnO2. Moreover, inclusion of small non-hydrated Li+ (ionic radius = 0.9 Å) was unable to prevent from forming α-MnO2 phase leading to relatively poor electrochemical performance.
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Crawford, Kevin G. "Surface transfer doping of diamond using transition metal oxides". Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8561/.
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This thesis presents a body of work which advances the use of single crystal hydrogen terminated diamond as a semiconducting material. Surface transfer doping of intrinsic diamond is investigated, examining the current state of this technology and its limitations. New techniques for producing robust, thermally stable surface transfer doped diamond were achieved through use of transition metal oxides such as MoO3 and V2O5, as demonstrated experimentally by way of Hall measurement. Through use of these materials, thermal stability was greatly increased up to temperatures of at least 300oC. To achieve this higher temperature operation, encapsulation of MoO3 and V2O5 was found to be necessary in maintaining conductivity of the diamond surface due to suspected thermally-induced loss of hydrogen termination. Similarly, long term atmospheric stability is shown to necessitate annealing of the diamond surface prior to oxide deposition and for thinner layers of oxide, down to 10 nm, encapsulation of the oxide to isolate from atmosphere is shown to be required for increased stability. As well as the improvements in stability offered by these transition metal oxides, sheet resistance of the hydrogen terminated diamond surface was also greatly reduced. Carrier densities as high as ~7.5 ×1013 cm-2 were observed for MoO3-induced surface transfer doping, resulting in a low sheet resistance of ~ 3 kΩ/□. In parallel to the development of oxide acceptor materials, conditioning of the diamond surface was explored using Atomic Force Microscopy (AFM). Techniques for smoothing the surface after mechanical polishing were developed by way of RIE and ICP etching using both chlorine and oxygen mixtures. Surface roughness down to 2 angstroms was demonstrated, showing a significant improvement in roughness over mechanical polishing alone. Similarly, observed defects produced by polishing induced damage were removed through use of this etching strategy. The effects of varied plasma density during hydrogen termination was explored on etched surfaces, which produced higher quality hydrogen-terminated surfaces as verified by surface conductivity and AFM measurements. Finally, incorporation of MoO3 into a preliminary Field Effect Transistor (FET) device on diamond was attempted. Fabrication techniques to produce a FET device on hydrogen-terminated diamond is shown with preliminary results of MoO3 encapsulated devices. Insights into the fabrication of ohmic and gate contacts, incorporating MoO3, is also discussed.
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Brammall, M. I. "Stoner criteria in transition metal oxides and heavy fermions". Thesis, University of Birmingham, 2011. http://etheses.bham.ac.uk//id/eprint/1648/.
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This thesis is an examination of the uses of mean-field theory in problems of the theory of strongly-correlated electronic systems, particularly to the problem of orbital ordering in transition metal oxides. We will apply mean-field theory to various models for orbital ordering of transition metal oxides, and also show that mean-field theory is not as bad an approximation as it might initially seem. We are also interested modelling superconductivity in heavy fermion systems. We conclude from our modelling on transition metal oxides that the mean-field theory we use based on the Stoner criterion will not be adequate to model such complicated phenomena. We propose an alternate mean-field theory based on non-linear fermionic transformations which we introduce. We suggest further improvements in the form of a non-orthogonal transformation, which we also introduce. As a diversion, we model frustrated antiferromagnetism on a pyrochlore lattice. The particular material is Gd\(_2\)Ti\(_2\)O\(_7\). We show that there are many effects in competition with each other. We conclude with a proposed magnetic structure which appears to be a better fit to experimental data than previous suggestions.
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Zhou, Fei Ph D. Massachusetts Institute of Technology. "Models for transition metal oxides and for protein design". Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/39558.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.Includes bibliographical references (p. 133-156).
A large number of properties of solid state materials can now be predicted with standard first-principles methods such as the Local Density (LDA) or Generalized Gradient Approximation (GGA). However, known problems exist when using these methods for predicting the electronic structure and total energy of transition metal oxides. We demonstrate that the LDA+U method, in which localized d electrons are treated with a Hubbard-like model, gives considerably better predictions in band gap, magnetization, lattice constants, redox potential, mixing energy and other properties of lithium transition-metal oxides. The systematic improvement of both electronic structure and total energy properties suggests that the more accurate treatment of electron correlation on the transition metal sites will greatly enhance the predictive character of ab-initio methods for these materials. In a even more dramatic example, the more accurate electronic and total energy descriptions with LDA+U have enabled us to study the finite temperature phase diagram of LixFePO4. It is found that an unexpected solid solution phase are mainly stabilized by the entropy contribution of localized d electrons. This brings the less visited problem of the effects of electronic correlation on thermodynamics into our attention.
(cont.) The second part of this thesis is focused on application of methods used in solid state materials to proteins. Protein systems are well known for having extremely large conformation space, which makes their energy evaluation expensive even with empirical energy models. We are implementing a coarse graining scheme, called the cluster expansion, to help alleviate this problem. Traditionally, the cluster expansion is a powerful tool to model the energetics of solid-state materials with configurational disorder. We have developed a generalized cluster expansion framework suitable for protein studies, in which properties such as the energy can be unambiguously expanded in the amino acid sequence space. The cluster expansion coarse-grains over non-sequence degrees of freedom (e.g. sidechain configurations) and thereby simplifies the problem of designing proteins, or predicting the compatibility of a sequence with a given structure, by many orders of magnitude. With the help of this method, we have been able to perform a full-sequence design for a small peptide within a relatively short period of time.
by Fei Zhou.
Ph.D.
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Forrest, T. R. C. "Ordering and dynamics of strongly correlated transition metal oxides". Thesis, University College London (University of London), 2010. http://discovery.ucl.ac.uk/20216/.
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This thesis describes a series of synchrotron based X-ray experiments on the lattice dynamics or magnetic ordering of several strongly correlated electron systems. Firstly, it will provide an introduction to the strongly correlated electron materials that were studied. After which a description of the experimental techniques used, specifically resonant X-ray scattering (RXS) and X-ray inelastic scattering (IXS), will be given. Finally the results of these experiments will be set out and evaluated. The experiments were as follows: X-ray inelastic scattering measurements on the effects of fluorine doping on the lattice dynamics of the newly discovered iron pnictide superconducting compound, SmFeAsO0.6F0.35 and its antiferromagnetic parent compound, SmFeAsO. The results from these experiments demonstrate the importance of antiferromagnetic fluctuations in understanding the lattice dynamics of this class of crystals. This result has been demonstrated for the ‘122’ class of pnictide crystals, but until now has not been shown for the ‘1111’ class of pnictides. Resonant X-ray scattering in the vicinity of the Mn L2 and L3 resonant enhancements was used to reassess the magnetic structure of multiferroic TbMnO3. The results indicate that the commonly accepted magnetic structure is modified, with additional a and c axis magnetic components. Therefore the ferroelectric polarisation in TbMnO3 arises from a phase transition between two non-collinear magnetic structures. It was previously believed that this phase transition was between a collinear and a non-collinear magnetic structure. Resonant X-ray scattering measurements were also taken on TbMnO3’s sister compound, DyMnO3. Data was recorded at the Mn K and Dy L3 resonant enhancements. Several unidentified incommensurate reflections, independent of this compound’s magnetic phases, were detected with photon energies close to the Mn K edge. What these reflections represent is still a mystery, although they do make a compelling case for further experimental work.
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Dixon, Edward. "The anion chemistry of transition metal oxides and oxychlorides". Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:3ddb2e1e-18e9-427a-a4a3-b7f2eba2489f.
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This investigation is based on the topotactic reduction reactions of 3 sets of phases: La₁-ₓSrₓMnO₃ (0.6 ≤ x ≤ 1), La₁-ₓCaₓMnO₃ (0.6 ≤ x ≤ 1) and Sr₃Fe₂-ₓCoₓO₅Cl₂ (0 ≤ x ≤ 1). The topotactic reduction reactions of La₁-ₓSrₓMnO₃ (0.6 ≤ x ≤ 1) perovskite phases using NaH as a solid state reducing agent result in the formation of reduced phases which contain manganese centres with a constant average oxidation state of +2.5, thus leading to an empirical composition of La₁-ₓSrₓMnO₃-(0.5+x)/2. The structures of the reduced phases contain a 6-layer OOTOOT’ stacking sequence of the octahedral (O) and tetrahedral (T) sheets and so are closely related to the 4-layer OTOT’-stacked brownmillerite structure. Close inspection reveals that the structures of the La₁-ₓSrₓMnO₃-y (x = 0.67, 0.7 and 0.75) reduced phases contain an intralayer ordered arrangement of twisted tetrahedral chains, and are the first instances of refined 6-layer structures containing such an arrangement. The driving force dictating the arrangement of the twisted tetrahedral chains in these 6-layer structures are shown to be the size of the tetrahedral chain dipole moment and the coupling between neighbouring tetrahedral layers in a similar manner to the brownmillerite structure. This logic has been applied to rationalise the ordering arrangement of the twisted tetrahedral chains in other structures containing tetrahedral layers. Variable temperature neutron diffraction data reveal that the La₁-ₓSrₓMnO₃-y (0.67 ≤ x ≤ 0.83) reduced phases adopt magnetically ordered structures incommensurate with the nuclear structures below TN. In contrast, the structures adopted by reduced phases formed by topotactic reduction reactions of La₁-ₓCaₓMnO₃ (0.6 ≤ x ≤ 1) perovskite phases using NaH are split into 2 groups as a function of the La:Ca ratio: The reduction of perovskite phases in the range (0.6 ≤ x ≤ 0.8) result in the formation of reduced phases with an empirical composition of La₁-ₓCaₓMnO₂ which adopt structures containing a disordered arrangement of layers of edge-sharing MnO₆ octahedra and layers of vertex-sharing MnO₄ tetrahedra. In contrast, reduction of the perovskite phases in the range (0.9 ≤ x ≤ 1) result in the formation of reduced phases with an empirical composition of (La₁-ₓCₓx)0.5Mn
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Popa, Andreia Ioana. "Electrochemistry and magnetism of lithium doped transition metal oxides". Doctoral thesis, Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden, 2009. https://tud.qucosa.de/id/qucosa%3A25180.
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The physics of transition metal oxides is controlled by the combination and competition of several degrees of freedom, in particular the charge, the spin and the orbital state of the electrons. One important parameter responsible for the physical properties is the density of charge carriers which determines the oxidization state of the transition metal ions. The central objective in this work is the study of transition metal oxides in which the charge carrier density is adjusted and controlled via lithium intercalation/deintercalation using electrochemical methods. Lithium exchange can be achieved with a high degree of accuracy by electrochemical methods. The magnetic properties of various intermediate compounds are studied.
Among the materials under study the mixed valent vanadium-oxide multiwall nanotubes represent a potentially technologically relevant material for lithium-ion batteries. Upon electron doping of VOx-NTs, the data confirm a higher number of magnetic V4+ sites. Interestingly, room temperature ferromagnetism evolves after electrochemical intercalation of Li, making VOx-NTs a novel type of self-assembled nanoscaled ferromagnets. The high temperature ferromagnetism was attributed to formation of nanosize interacting ferromagnetic spin clusters around the intercalated Li ions. This behavior was established by a complex experimental study with three different local spin probe techniques, namely, electron spin resonance (ESR), nuclear magnetic resonance (NMR) and muon spin relaxation spectroscopies.
Sr2CuO2Br2 was another compound studied in this work. The material exhibits CuO4 layers isostructural to the hole-doped high-Tc superconductor La2-xSr2CuO4. Electron doping is realized by Li-intercalation and superconductivity was found below 9K. Electrochemical treatment hence allows the possibility of studying the electronic phase diagram of LixSr2CuO2Br2, a new electron doped superconductor. The effect of electrochemical lithium doping on the magnetic properties was also studied in tunnel-like alpha-MnO2 nanostructures. Upon lithium intercalation, Mn4+ present in alpha-MnO2 will be reduced to Mn3+, resulting in a Mn mixed valency in this compound. The mixed valency and different possible interactions arising between magnetic spins give a complexity to the magnetic properties of doped alpha-MnO2.
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Raikar, Ganesh Narayan. "Auger lineshape analysis of semiconductors and transition-metal oxides". Thesis, Raikar, Ganesh Narayan (1987) Auger lineshape analysis of semiconductors and transition-metal oxides. PhD thesis, Murdoch University, 1987. https://researchrepository.murdoch.edu.au/id/eprint/51560/.
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This work deals with the experimental investigation of the surfaces of some of the technologically important semiconductors such as a-Si:H, InP, Zn3P2, CdS and FeS2, and transition-metal oxides such as Fe2O3, CO3O4, NiO and CuO, using Auger lineshape analysis (ALA) with a view to assessing its suitability to extract the local density of states (LDOS) information.
In addition, ALA has also been used as a probe of the local chemical environment. Chemical bonding effects are reflected in both the shape and intensity of the Auger peaks. The Auger process samples only the occupied DOS and the CVV lineshapes should reflect a fold of the ground state DOS when hole-hole interaction and other complicating effects are small. Although other spectroscopic techniques such as Xray photo-electron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) (also called core loss spectroscopy (CLS)) have been occasionally utilised in this work, the primary emphasis is placed on ALA.
The van Cittert iterative deconvolution technique has been used to recover the intrinsic Auger lineshape from the experimental data. This technique has been extensively tested on both the synthetic data as well as real data from copper and aluminium and the results are in good agreement with the published literature.
Interpretation of the deconvoluted data has been in terms of one electron theoretical DOS and/or the data from XPS and SXE (soft X-ray emission). In addition, the Cini-Sawatzky theory has also been used via the effective hole-hole interaction, Ueff' to distinguish between "bandlike" and "quasiatomic" like Auger lineshapes.
Oxygen chemisorption is studied on InP, Zn3P2 and FeS2 and substantial changes are observed in the CVV Auger lineshapes. These changes are related to changes in the chemical environment of the surface atoms and associated changes in the valence band DOS. The new peaks that arise on the low kinetic energy side of the P L2,3VV Auger line in InP and ZnsP2 are accounted for in terms of both the interatomic and the molecular orbital (MO) transitions. The splitting of Fe M2, 3VV Auger line in FeS2 upon chemisorption has been explained in terms of the "autoionisation" process.
The valence band density of states (VBDOS) of InP and ZnsP2 has also been studied using XPS. Some of the discrepancies in the previous interpretation of the XPS data of ZnsP2 have been addressed.
The main objectives of extracting local density of states and chemical information have been fulfilled to a great extent. Many of the surfaces studied in this work have not been analysed in this way previously. The main conclusion of this work is that ALA can be used successfully on a broad range of semiconductor materials to obtain band structural and chemical information.
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