Дисертації з теми "Novel Oxides - Structural Properties"

AFM materials with triangular cationic sublattices give rise to geometric magnetic frustration. The goal of this project is to study frustrated systems by designed and synthesis of more frustrated systems. For this purpose, the 5d system of osmium transition metal oxide was chosen. The osmium-based compounds are then successfully synthesized using the conventional solid state method. The crystal structures are then characterized by different techniques such as X-ray diffraction and neutron diffraction. To determine the ordering of the crystal systems, magnetic susceptibility and heat capacity measurements are carried out. By employing the spin dimer analysis, magnetic exchange interactions are calculated. These novel osmium-based ordered rock salt structure type systems are then being compared to similar crystal systems in the text.

There is great interest in the development of new polar dielectric ceramics and multiferroic materials with new and improved properties. A family of tetragonal tungsten bronze (TTB) relaxors of composition Ba₆M³⁺Nb₉O₃₀ (M³⁺ = Ga³⁺, Sc³⁺ and In³⁺, and also their solid solutions) were studied in an attempt to understand their dielectric properties to enable design of novel polar TTB materials. A combination of electrical measurements (dielectric and impedance spectroscopy) and powder diffraction (X-ray and neutron) studies as a function of temperature was employed for characterising the dynamic dipole response in these materials. The effect of B-site doping on fundamental dipolar relaxation parameters were investigated by independently fitting the dielectric permittivity to the Vogel-Fulcher (VF) model, and the dielectric loss to Universal Dielectric Response (UDR) and Arrhenius models. These studies showed an increase in the characteristic dipole freezing temperature (T[subscript(f)]) with increase B-cation radius. Crystallographic data indicated a corresponding maximum in tetragonal strain at T[subscript(f)], consistent with the slowing and eventual freezing of dipoles. In addition, the B1 crystallographic site was shown to be most active in terms of the dipolar response. A more in-depth analysis of the relaxor behaviour of these materials revealed that, with the stepwise increase in the ionic radius of the M³⁺ cation on the B-site within the Sc-In solid solution series, the Vogel-Fulcher curves (lnf vs. T[subscript(m)]) are displaced to higher temperatures, while the degree of relaxor behaviour (frequency dependence) increases. Unfortunately, additional features appear in the dielectric spectroscopy data, dramatically affecting the Vogel-Fulcher fitting parameters. A parametric study of the reproducibility of acquisition and analysis of dielectric data was therefore carried out. The applicability of the Vogel-Fulcher expression to fit dielectric permittivity data was investigated, from the simple unrestricted (“free”) fit to a wider range of imposed values for the VF relaxation parameters that fit with high accuracy the experimental data. The reproducibility of the dielectric data and the relaxation parameters obtained by VF fitting were shown to be highly sensitive to the thermal history of samples and also the conditions during dielectric data acquisition (i.e., heating/cooling rate). In contrast, UDR analysis of the dielectric loss data provided far more reproducible results, and to an extent was able to partially deconvolute the additional relaxation processes present in these materials. The exact nature of these additional relaxations is not yet fully understood. It was concluded application of the Vogel-Fulcher model should be undertaken with great care. The UDR model may represent a feasible alternative to the evaluation of fundamental relaxation parameters, and a step forward towards the understanding of the dielectric processes in tetragonal tungsten bronzes.

Thesis (Ph. D.)--Materials Science and Engineering, Georgia Institute of Technology, 2008.
Peter J. Hesketh, Committee Member ; Zhong Lin Wang, Committee Chair ; C.P. Wong, Committee Member ; Robert L. Snyder, Committee Member ; Christopher Summers, Committee Member.

Metal oxides are of immense technological importance. Their wide variety of structural and electronic characteristics leads to a flexibility unrivalled by other groups of materials. However, there is still much debate about the fundamental properties of some of the most widely used oxides, including TiO₂ and In₂O₃. This work presents high quality, in-depth characterisation of these two oxides in pure and doped form, including soft and hard X-ray photoelectron spectroscopy and X-ray diffraction. Bulk samples as well as thin film samples were prepared analysed. For the preparation of thin films a high quality sol-gel dip-coating method was developed, which resulted in epitaxial films. In more detail the organisation of the thesis is as follows: Chapter 1 provides an introduction to key ideas related to metal oxides and presents the metal oxides investigated in this thesis, In₂O₃, Ga₂O₃, Tl₂O₃, TiO₂, and SnO₂. Chapter 2 presents background information and Chapter 3 gives the practical details of the experimental techniques employed. Chapters 4 presents reciprocal space maps of MBE-grown In₂O₃ thin films and nanorods on YSZ substrates. Chapters 5 and 6 investigate the doping of In₂O₃ bulk samples with gallium and thallium and introduce a range of solid state characterisation techniques. Chapter 7 describes the development of a dip-coating sol-gel method for the growth of thin films of TiO₂ and shows 3D reciprocal space maps of the resulting films. Chapter 8 concerns hard x-ray photoelectron spectroscopy of undoped and Sn-doped TiO₂. Chapter 9 interconnects previous chapters by presenting 2D reciprocal space maps of nano structured epitaxial samples of In₂O₃ grown by the newly developed sol-gel based method. Chapter 10 concludes this thesis with a summary of the results.

Zirconia powders doped with different amounts of dopants (CeO2, Gd2O3, and CaO) were synthesized by a citrate technique. X-ray diffraction for samples sintered at 1500 °C revealed that the zirconia ceramics were stabilized in the cubic phase above 12 mole % CaO and 10 mole % Gd2O3, while tetragonal zirconia is obtained above 15 mole % CeO2. Relative densities up to 99.5% were obtained. The effect of dopant concentration on the lattice parameter, average crystallite size, microstrain was studied. The cubic lattice parameter increases nearly linearly with increasing the concentration in case of CaO and Gd2O3. The tetragonal lattice parameters at and ct increase nearly linearly with increasing the concentration of CeO2. The average crystallite size was found to be larger than 600 nm for the samples investigated.

Zirconia powders doped with different amounts of dopants (CeO2, Gd2O3, and CaO) were synthesized by a citrate technique. X-ray diffraction for samples sintered at 1500 °C revealed that the zirconia ceramics were stabilized in the cubic phase above 12 mole % CaO and 10 mole % Gd2O3, while tetragonal zirconia is obtained above 15 mole % CeO2. Relative densities up to 99.5% were obtained. The effect of dopant concentration on the lattice parameter, average crystallite size, microstrain was studied. The cubic lattice parameter increases nearly linearly with increasing the concentration in case of CaO and Gd2O3. The tetragonal lattice parameters at and ct increase nearly linearly with increasing the concentration of CeO2. The average crystallite size was found to be larger than 600 nm for the samples investigated.

In the potential event of a clad breach in a Sodium-cooled Fast Reactor (SFR), the sodium metallic coolant could come into contact with the (U,Pu,Np)$O_2$ nuclear fuel. The reaction products are numerous, but there is little knowledge of their structural and thermodynamic properties. Under the oxygen potential conditions of the reactor, pentavalent $Na_3AnO_4$ (An=U,Pu,Np) is expected to form, but its structure was the subject of controversy until now. We showed that $\alpha-Na_3UO_4$ adopts a monoclinic symmetry in space group $\textit{P2/c}$. Neutron diffraction combined with X-ray Absorption Near Edge Structure (XANES) spectroscopy at the U-M$_4$ edge also revealed that this phase could accommodate excess sodium on the uranium site, with subsequent charge compensation of the uranium cation from U(V) to U(VI), which was not previously foreseen. The corresponding mixed valence state composition is written $Na_3(U_{1-x},Na_x)O_4$ with 0<$\textit{x}$<0.16(2). To complete the data on the Na-U-O system, the thermodynamic functions of $Na_2U_2O_7$ and $Na_4UO_5$ were evaluated using Knudsen effusion mass spectrometry (KEMS) and thermal-relaxation calorimetry. In addition, the oxygen content required at 900 K within liquid sodium to form pentavalent $Na_3UO_4$ and hexavalent $Na_4UO_5$ were calculated to be 0.7 and 1.5 wppm, respectively, which are levels typically encountered in SFRs. A thermodynamic model for the Np-O system was then developed using the CALPHAD method. This is particularly relevant since it is envisaged to incorporate minor actinides into the fuel to minimize the nuclear waste inventory. The poorly known structures of the Na- Np-O and Na-Pu-O phases diagrams, i.e., tetravalent $Na_2AnO_3$ (An=Np,Pu), pentavalent $Na_3AnO_4$, hexavalent $Na_4AnO_5$ and $\alpha-Na_2NpO_4$, and heptavalent $Na_5AnO_6$, were also re-fined by the Rietveld method. The structures of $Na_3NpO_4$ and $Na_3PuO_4$ were determined ab initio from powder X-ray diffraction data, and found to be orthorhombic in the space group $\textit{Fmmm}$. The valence states of the neptunium cations were confirmed from the isomer shift values of their Mössbauer spectra. Having established the charge states without ambiguity, XANES spectra were collected at the $Np-L_3$ and $Pu-L_3$ edges to serve as reference data for An(V), An(VI), and An(VII) oxide phases in the solid state. Finally, KEMS studies of $\alpha-Na_2NpO_4$ showed very promising results for the determination of the enthalpies of formation of the sodium neptunates and plutonates, for which there is almost no data available. The heat capacities and entropies at 298.15 K of $\alpha-Na_2NpO_4$, $Na_4NpO_5$, $Na_5NpO_6$, and $Na_5PuO_6$ were also determined. Comparing their Gibbs energy values, the sodium neptunates were found to be slightly more stable than their isostructural uranium analogues.

Low-dimensional spin systems with S = 1/2 and a singlet ground state attract intensive research efforts because of the quantum nature of their ground state. Since the discovery of the singlet plaquette CaV4O9 compound more attention has been paid to chemical analogues with S = 1/2, V4+ (d1) ions. For example, the V2O5 network exhibits the characteristics of layered and crystallographic shear structures and there is a large vanadium oxide bronze family, MxV2O5 (M = alkali, alkaline earth metals), which shows several original [V2O5] networks. For this reason, the atomic architectures of V2O5 and its derivatives provide a stage where various lower-dimensional quantum critical phenomena can be realised. Compounds in the series LixV2O5 were synthesised via soft chemistry methods and characterised structurally and magnetically via high-resolution x-ray and neutron diffraction and magnetization measurements using a SQUID magnetometer. Additional weaker peaks observed in certain of the diffraction patterns suggested the occurrence of charge ordering of vanadium ions in an incommensurately modulated superstructure for some of the E-LixV2O5 and E'-LixV2O5 phases. Having discovered a possible magnetic transition (Tf ~ 25 K) in one of these dilute-spin phases, Li0.50V2O5, believed to be associated with the low-dimensional, chain-like arrangement of the V4+ (S = 1/2, d1) cations over the non-magnetic V5+(S = 0, d0) network, a local probe, SR, was applied to investigate its ground state and the ground states of other members of the series LixV2O5 with x = 0.55, 0.64 and 0.72 which also exhibit interesting magnetic behaviour. Lack of oscillation in the SR data revealed the absence of any long-range magnetic order for Li0.50V2O5, Li0.55V2O5, Li0.64V2O5, and Li0.72V2O5, supportive of a true one-dimensional ground state, suggesting the formation of domains of one-dimensional antiferromagnetic chains, consistent with the Bonner-Fisher model for low-dimensional magnetic behaviour which provided a good fit to the SQUID data collected.

The thesis entitled "Layered Oxides and Phosphates of Bismuth: New Structural Types and Related Properties" consists of three parts and six chapters. It begins with an introductory note providing a brief overview of the existing literature on bismuth based layered oxides. Part A of the thesis describes novel variants of the Aurivillius, Scheelite and Fluorite related phases with special emphasis on photocatalytic behavior of these materials. Chapter 1 describes two new compounds, LiBi4Nb3O14 and LiBi4Ta3O14 characterized by single crystal X-ray diffraction to depict a unique structure, which have similarities with both an ideal Aurivillius phase and a typical hexagonal tungsten bronze. Photo-degradation of a wide range of water pollutants, which include commonly, used dyes in textile industry and phenols suggest selectivity of LiBi4Nb3O14 towards hydroxyl group containing aromatic compounds. Chapter 2, Section 1 presents the structure of BaBi2Mo4O16 as a new compound among Scheelites, which shows high selectivity towards photo-degradation of non- chloro-containing aromatic systems. Further, the degradation rates are found to be significantly higher than the commercial TiO2 catalyst for nitro and methyl phenols. The solid solution, BaBi2Mo4-xWxO16 (0.25 ≤ x ≤ 1) has been analyzed to obtain insights into the compositional aspects. Section 2 has a detailed discussion on the structural stability of the Scheelite BaBi2Mo4O16 upon substitution of divalent cations, Ca, Sr and Pb at the barium site. The potential of these compounds as photocatalytic materials has been investigated. Chapter 3 describes a detailed kinetic analysis along with a single crystal X-ray structure determination of Ba2Bi24Mo10O68. Substitution at the Bi site by Ba and La results in differences in photocatalytic activity. All variants are observed to show specificity towards nitro- substitution at the ortho- position in phenols. Chapter 4 is a re-determination of the crystal structures of the triclinic polymorphs of BiNbO4 and BiTaO4 since one of the earlier reports is on a twinned crystal with large, unacceptable thermal ellipsoids and the other is a powder data -based Rietveld refinement of this model. Further BiNbO4 has been investigated to evaluate selectivity in photo degradation of dyes. In Part B, an attempt to correlate the crystal structure with relaxor ferroelectric behavior is outlined. Chapter 5 investigates a bismuth based tetratungsten bronze (TTB) relaxor material for the first time. Single crystal X-ray diffraction studies on the composition, x = 0.77 of the solid solution, Ba5x/2Bi(1-x)5/3Nb5O15 (0.52 ≤ x ≤ 0.8) depicts disorder in the occupancies of barium and bismuth atoms which is suggested to be the possible origin for relaxor behavior. Dielectric measurements correlate the structural features. Part C consists of a structure-based analysis on possible correlations with ionic conductivity. Chapter 6 describes two new crystal structures, Bi17P8O45.5 and Bi20P8O50, and the evolution of the series, Bi16+xP8O45+(3x-2)/2 (0.7 ≤ x ≤ 4.0). A rationale for the low ionic conductivity exhibited in these materials is arrived at from the arrangement of atoms in the crystal structure. Appendix A consists of a description of the crystal structure and ionic conductivity of Bi3W2O10.5.

The thesis entitled "Layered Oxides and Phosphates of Bismuth: New Structural Types and Related Properties" consists of three parts and six chapters. It begins with an introductory note providing a brief overview of the existing literature on bismuth based layered oxides. Part A of the thesis describes novel variants of the Aurivillius, Scheelite and Fluorite related phases with special emphasis on photocatalytic behavior of these materials. Chapter 1 describes two new compounds, LiBi4Nb3O14 and LiBi4Ta3O14 characterized by single crystal X-ray diffraction to depict a unique structure, which have similarities with both an ideal Aurivillius phase and a typical hexagonal tungsten bronze. Photo-degradation of a wide range of water pollutants, which include commonly, used dyes in textile industry and phenols suggest selectivity of LiBi4Nb3O14 towards hydroxyl group containing aromatic compounds. Chapter 2, Section 1 presents the structure of BaBi2Mo4O16 as a new compound among Scheelites, which shows high selectivity towards photo-degradation of non- chloro-containing aromatic systems. Further, the degradation rates are found to be significantly higher than the commercial TiO2 catalyst for nitro and methyl phenols. The solid solution, BaBi2Mo4-xWxO16 (0.25 ≤ x ≤ 1) has been analyzed to obtain insights into the compositional aspects. Section 2 has a detailed discussion on the structural stability of the Scheelite BaBi2Mo4O16 upon substitution of divalent cations, Ca, Sr and Pb at the barium site. The potential of these compounds as photocatalytic materials has been investigated. Chapter 3 describes a detailed kinetic analysis along with a single crystal X-ray structure determination of Ba2Bi24Mo10O68. Substitution at the Bi site by Ba and La results in differences in photocatalytic activity. All variants are observed to show specificity towards nitro- substitution at the ortho- position in phenols. Chapter 4 is a re-determination of the crystal structures of the triclinic polymorphs of BiNbO4 and BiTaO4 since one of the earlier reports is on a twinned crystal with large, unacceptable thermal ellipsoids and the other is a powder data -based Rietveld refinement of this model. Further BiNbO4 has been investigated to evaluate selectivity in photo degradation of dyes. In Part B, an attempt to correlate the crystal structure with relaxor ferroelectric behavior is outlined. Chapter 5 investigates a bismuth based tetratungsten bronze (TTB) relaxor material for the first time. Single crystal X-ray diffraction studies on the composition, x = 0.77 of the solid solution, Ba5x/2Bi(1-x)5/3Nb5O15 (0.52 ≤ x ≤ 0.8) depicts disorder in the occupancies of barium and bismuth atoms which is suggested to be the possible origin for relaxor behavior. Dielectric measurements correlate the structural features. Part C consists of a structure-based analysis on possible correlations with ionic conductivity. Chapter 6 describes two new crystal structures, Bi17P8O45.5 and Bi20P8O50, and the evolution of the series, Bi16+xP8O45+(3x-2)/2 (0.7 ≤ x ≤ 4.0). A rationale for the low ionic conductivity exhibited in these materials is arrived at from the arrangement of atoms in the crystal structure. Appendix A consists of a description of the crystal structure and ionic conductivity of Bi3W2O10.5.

The materials synthesised in this study were designed to have novel morphology coupled with a tightly controlled surface composition that could be varied depending on a application. Preparations with simple single metal oxides (i.e. TiO2, SiO2, Al2O3 and ZrO2) were used as the starting point with the latter stages involving multi-metal oxide coatings and materials. The research was divided into three interconnected areas; i) biotemplating, ii) alternative synthetic morphologies to biotemplating and iii) the synergy between microparticles and insecticides. For the investigation into biotemplating pollen was chosen as the main example due to its ubiquity. Here, good replication of its structure with metal oxides can be achieved by two-dimensional solgel chemistry. Such materials can be further modified to have tunable surface chemistry through dopants and optical properties (i.e. fluorescence) through the use of dyes. Materials were extensively characterised using primarily spectroscopy (UV and IR) and microscopy (i.e. SEM coupled with EDX elemental analysis). These were considered for several applications and examples investigated here included as a taggant technology and photocatalytic removal of methyl orange in an aqueous environment (TiO2-pollen only). For the latter, results have been compared with those of a commercially available alternative (P25) where the preliminary results are very promising. The method of overcoating was also shown to be transferrable to other flora and fauna biotemplates. Synthetic alternatives for the biotemplated pollen were considered in the second investigative area where solution sol-gel processes such as the Stöber method were considered in addition to other suspension based precipitation methods (i.e. refluxes and microemulsions). Processes developed in the biotemplating research were applied here and analysed again using spectroscopy and microscopy as the main techniques. As part of this aspect, a novel fast-drying water-in-oil microemulsion delivery and preparative system was also developed using low boiling point solvents such as isopentane and ethanol and low toxicity sucrose ester surfactants. Hollow oxide shells could be prepared in these using a novel low-temperature route that were comparable in thickness (but significantly smaller in size) to hollow pollen replicas. In this second area attention was shifted to more focus on oxides of Si and Al (as opposed to TiO2 that used extensively in biotemplating) to broaden the scope of the research and investigate other potential applications, such as nanoabrasives (surface roughness and ability to cleave DNA). The third and final area of interest used the materials from the previous two aspects in coatings that were applied to investigating the knockdown (KD) and total mortality (TM) of selected arthropods. Here mosquitoes of the A. Gambiae and S. Aegypti genus were considered with particular focus on synergistic effects with existing commercial insecticides (using mainly CDC bottle tests). Microscopy was used as the primary characterisation technique here to determine particle transfer after each assay. In these tests %TM suggested SiO2 microspheres were particularly effective at in enhancing mortality of the commercial l-cyhalothrin insecticide. Additionally, novel methods of recording mosquito behaviour was investigated through optical and thermographic stills and videos.

The phase relations in three oxide systems; ZnO–BiVO4, Pb2V2O7–BiVO4 and PbO– BiVO4, have been studied and their phase diagrams over the whole component concentration range up to 1273 K have been established. As a result of solid-state reaction between ZnO and BiVO4 mixed at a molar ratio of 2:1 or among ZnO, V2O5 and Bi2O3, mixed at a molar ratio of 4:1:1, a new double vanadate BiZn2VO6 has been obtained. Its crystallographic system was determined, its unit cell parameters were calculated and its incongruent melting temperature was established. A new compound is also formed in the Pb2V2O7–BiVO4 system. It has been shown that BiVO4 and Pb2V2O7 react with each other forming a compound of the formula Pb2BiV3O11, when their molar ratio is equal to 1:1, or between PbO, Bi2O3 and V2O5, mixed at a molar ratio of 4:1:3. This material melts congruently and it crystallises in the triclinic system. A new series of non-stoichiometric sulphides Ga1-xGexV4S8 (0 x 1) has been synthesised by standard solid-state reaction. The samples have been characterised by powder X-ray and neutron diffraction, SQUID magnetometry and electrical transportproperty measurements. Structural analysis reveals that a solid solution is formed throughout this composition range. Magnetic measurements suggest that the ferromagnetic behaviour of the end-member phase GaV4S8 is retained at x 0.7. By contrast Ga0.25Ge0.75V4S8 appears to undergo antiferromagnetic ordering at ca. 15 K. All materials with x ¹ 1 are n-type semiconductors whose resistivity falls by almost six orders of magnitude with decreasing gallium content, whilst the end-member phase GeV4S8 is a ptype semiconductor. Powder neutron diffraction studies show that the cubic unit cell is retained for non-stoichiometric materials to the lowest temperatures studied. Single crystals of five erbium-chromium sulphides have been grown by chemical vapour transport using iodine as the transporting agent. Single-crystal X-ray diffraction reveals that in Er3CrS6, octahedral sites are occupied exclusively by Cr3+ cations, leading to onedimensional CrS4 5- chains of edge-sharing octahedra, whilst in Er2CrS4, Er3+ and Cr2+ cations occupy the available octahedral sites in an ordered manner. By contrast, in Er6Cr2S11, Er4CrS7 and Er8Cr3S15, Er3+ and Cr2+ ions are disordered over the octahedral sites. In Er2CrS4, Er6Cr2S11, Er4CrS7 and Er8Cr3S15, the network of octahedra generates an anionic framework constructed from M2S5 slabs of varying thickness, linked by onedimensional octahedral chains. This suggests that these four phases belong to a series in which the anionic framework may be described by the general formula [M2n+1S4n+3]x-, with charge balancing provided by Er3+ cations located in sites of high-coordination number within one-dimensional channels defined by the framework. Er4CrS7, Er6Cr2S11, Er8Cr3S15 ii and Er2CrS4 may thus be considered as the n = 1, 2, 3 and members of this series. Whilst Er4CrS7 is paramagnetic, successive magnetic transitions associated with ordering of the chromium and erbium sub-lattices are observed on cooling Er3CrS6 (TC(Cr) = 30 K; TC(Er) = 11 K) and Er2CrS4 (TN(Cr) = 42 K, TN(Er) = 10 K) whereas Er6Cr2S11 exhibits ordering of the chromium sub-lattice only (TN = 11.4 K). These four materials have been studied using neutron diffraction which allowed magnetic ordering to be examined.

Our understanding of the nature of Earth’s D” region was changed significantly by a recent finding by Murakami et al. (2004), who revealed a phase transition from perovskite to post-perovskite structure in MgSiO3 at about 125 GPa and 2500 K, corresponding to conditions of the lowermost mantle. A perovskite to post-perovskite phase transition accounts for many unusual features of the D” region, including its notable seismic anisotropy, and also accounts for the unusual topology of the D” discontinuity. However, the experimentally synthesised post-perovskite phase of MgSiO3 is not quenchable to ambient conditions, which means that many of its physical properties remain difficult to determine. On the other hand, there are several post-perovskite oxides, CaIrO3, CaPtO3, CaRhO3 and CaRuO3, which can be quenched to ambient conditions, maintaining their structure. High pressure synthesis of CaIr1-xPtxO3 solid solutions (x = 0, 0.3, 0.5, 0.7) and CaIr0.5Rh0.5O3 was conducted at the University of Edinburgh and Geodynamics Research Center, Ehime University, and structures and physical properties of these novel post-perovskite materials determined. Substantial [100] grain growth was observed in all solid solutions leading to pronounced texture even in powdered materials. Temperature-independent paramagnetism above 150 K and small magnetic entropy observed in heat capacity measurements suggest that CaIrO3 is an intrinsically weak itinerant ferromagnetic metal, while electrical resistivity measurements show that it is a narrow bandgap semiconductor, possibly due to grain boundary effects. CaIrO3 undergoes a magnetic transition at 108K and possesses a saturated magnetic moment of 0.04 μB. Doping with Pt or Rh induces Curie-Weiss paramagnetism and suppresses the magnetic transition. The anisotropic structure and morphology of CaIrO3 combined with the Ir4+ spin-orbit coupling results in a large magnetic anisotropy constant of 1.77 x 106 Jm-3, comparable to values for permanent magnet materials. A new high-pressure phase of CaIr0.5Pt0.5O3 was synthesised at 60GPa, 1900K using a laser-heated DAC (diamond anvil cell) at GRC, Ehime University. Its Raman spectra resemble those of perovskite phases of CaIrO3 and CaMnO3, implying that CaIr0.5Pt0.5O3 undergoes a post-perovskite to perovskite phase transition with increasing pressure. I estimate an increase in thermodynamic Grüneisen parameter γth across the post-perovskite to perovskite transition of 34 %, with similar magnitude to (Mg,Fe)SiO3 and MgGeO3, suggesting that CaIr0.5Pt0.5O3 is a promising analogue for experimentally simulating the competitive stability between perovskite and post-perovskite phase of magnesium silicates in Earth’s lowermost mantle. Such estimation is reliable since the estimated and directly calculated thermodynamic Grüneisen parameter γth from heat capacity show consistent values. The marked effect that Pt has on stabilising the post-perovskite structure in CaIr1-xPtxO3 solid solutions explains why the post-perovskite to perovskite phase transition has not been observed for CaPtO3 in contrast to other quenchable post-perovskite oxides: CaIrO3, CaRhO3 and CaRuO3.Work presented here demonstrates that CaIrO3 solid solutions can be used to provide new insight into factors stabilising post-perovskite structures in Earth’s lowermost mantle.

Transition metal compounds, especially the oxides, containing dn (0 ≤ n ≤ 10) electronic configuration, constitute the backbone of solid state/materials chemistry aimed at realization of novel materials properties of technological importance. Some of the significant materials properties of current interest are spin-polarized metallic ferromagnetism, negative thermal expansion, second harmonic nonlinear optical (NLO) susceptibility, fast ionic and mixed electronic/ionic conductivity for application in solid state batteries, and last but not the least, high-temperature superconductivity. Typical examples for each one of these properties could be found among transition metal oxides. Thus, alkaline-earth metal (A) substituted rare-earth (Ln) manganites, Lnı.xAxMnΟ3, are currently important examples for spin-polarized magnetotransport, ZrV2O7 and ZrW2O8 for negative thermal expansion coefficient, KTiOPO4 and LiNbO3 for second harmonic NLO susceptibility, (Li, La) TiO3 and LiMn2O4 for fast-ionic and mixed electronic/ionic conductivity respectively, and the whole host of cuprates typified by YBa2Cu3O7 for high Tc superconductivity. Solid state chemists constantly endeavour to obtain structure-property relations of solids so as to be able to design better materials towards desired properties. Synthesis coupled with characterization of structure and measurement of relevant properties is a common strategy that chemists adopt for this task. The work described in this thesis is based on such a broad-based chemists' approach towards understanding and realization of novel materials properties among the family of metal oxides. A search for metallic ferro/ferrimagnetism among the transition metal perovskite oxides, metallicity and possibility of superconductivity among transition-metal substituted cuprates and second order NLO susceptibility among metal oxides containing d° cations such as Ti(IV), V(V) and Nb(V) - constitute the main focus of the present thesis. New synthetic strategies that combine the conventional ceramic approach with the chemistry-based 'soft1 methods have been employed wherever possible to prepare the materials. The structures and electronic properties of the new materials have been probed by state-of-the art techniques that include powder X-ray diffraction (XRD) together with Rietveld refinement, electron diffraction, thermogravimetry, measurement of magnetic susceptibility (including magnetoresistance), Mossbauer spectroscopy and SHG response (towards 1064 nm laser radiation), besides conventional analytical techniques for determination of chemical compositions. Some of the highlights of the present thesis are: (i) synthesis of new mixed valent [Mn(III)/Mn(IV)] perovskite-type manganites, ALaMn2O6-y (A = K, Rb) and ALaBMn3O9_y (A = Na, K; B = Ca, Sr) that exhibit ferromagnetism and magnetoresistance; (ii) investigation of a variety of ferrimagnetic double-perovskites that include ALaMnRuO6 (A = Ca, Sr, Ba) and ALaFeVO6 (A = Ca, Sr) and A2FeReO6 (A = Ca, Sr, Ba) providing new insights into the occurrence of metallic and nonmetallic ferrimagnetic behaviour among this family of oxides; (iii) synthesis of new K2NiF4-type oxides, La2-2xSr2XCui.xMxO4 (M = Ti, Mn, Fe, Ru) and investigation of Cu-O-M interaction in two dimension and (iv) identification of the structural rnotif(s) that gives rise to efficient second order NLO optical (SHG) response among d° oxides containing Ti(IV), V(V), Nb(V) etc., and synthesis of a new SHG material, Ba2-xVOSi2O7 having the fresnoite structure. The thesis consists of five chapters and an appendix, describing the results of the investigations carried out by the candidate. A brief introduction to transition metaloxides, perovskite oxides in particular, is presented in Chapter 1. Attention is focused on the structure and properties of these materials. Chapter 2 describes the synthesis and investigation of two series of anion-deficient perovskite oxides, ALaMn2O6-y (A = K, Rb, Cs) and ALaBMn3O9_y (A = Na, K; B = Ca, Sr). ALaMn2O6-y (A = K, Rb, Cs) series of oxides adopt 2 ap x 2 ap superstructure for K and Rb phases and √2 av x √2 ap x 2 ap superstructure (ap = perovskite subcell) for the Cs phase. Among ALaBMn3O9-y phases, the A = Na members adopt a new kind of perovskite superstructure, ap x 3 ap, while the A = K phases do not reveal an obvious superstructure of the perovskite. All these oxides are ferromagnetic (Tc ~ 260-325 K) and metallic exhibiting a giant magnetoresistance behaviour similar to alkaline earth metal substituted lanthanum manganites, Lai_xAxMnO3. However, unlike the latter, the resistivity peak temperature Tp for all the anion-deficient manganites is significantly lower than Tc. In Chapter 3, we have investigated structure and electronic properties of double-perovskite oxides, A2FeReO6 (A = Ca, Sr and Ba). The A = Sr, Ba phases are cubic (Fm3m) and metallic, while the A = Ca phase is monoclinic (P2yn) and nonmetallic. All the three oxides are ferrimagnetic with Tcs 315-385 K as reported earlier. A = Sr, Ba phases show a negative magnetoresistance (MR) (10-25 % at 5 T), while the Ca member does not show an MR effect. 57Fe Mossbauer spectroscopy shows that iron is present in the high-spin Fe3+ (S = 5/2) state in Ca compound, while it occurs in an intermediate state between high-spin Fe2+ and Fe3+ in the Ba compound. Monoclinic distortion and high covalency of Ca-O bonds appear to freeze the oxidation states at Fe+3/Re5+ in Ca2FeRe O6, while the symmetric structure and ionic Ba-O bonds render the FeReO6 array highly covalent and Ba2FeReO6 metallic. Mossbauer data for Sr2FeReO6 shows that the valence state of iron in this compound is intermediate between that in Ba and Ca compounds. It is likely that Sr2FeReO6 which lies at the boundary between metallic and insulating states is metastable, phase-seperating into a percolating mixture of different electronic states at the microscopic level. In an effort to understand the occurrence of metallicity and ferrimagnetism among double perovskites, we have synthesized several new members : ALaMnFeO6 (A = Ca, Sr, Ba), ALaMnRuO6 (A = Ca, Sr, Ba) and ALaVFeO6 (A = Ca, Sr) (Chapter 3). Electron diffraction reveals an ordering of Mn and Ru in ALaMnRuO6 showing a doubling of the primitive cubic perovskite cell, while ALaVFeO6 do not show an ordering. ALaMnRuOs are ferrimagnetic (Tcs ~ 200-250 K) semiconductors, but ALaVFeO6 oxides do not show a long range magnetic ordering . The present work together with the previous work on double perovskites shows that only a very few of them exhibit both metallicity and ferrimagnetism, although several of them are ferrimagnetic. For example, among the series Ba2MReO6 (M = Mn, Fe, Co, Ni), only the M = Fe oxide is both metallic and ferrimagnetic, while M = Mn and Ni oxides are ferrimagnetic semiconductors. Similarly, A2CrMoO6 (A = Ca, Sr), A2CrRe06 (A = Ca, Sr), and ALaMnRuO6 (A = Ca, Sr, Ba) are all ferrimagnetic but not metallic. While ferrimagnetism of double perovskites arise from an antiferromagnetic coupling of B and B' spins through the B-O-B' bridges, the occurrence of metallicity seems to require precise matching of the energies of d-states of B and B' cations and a high covalency in the BB'O6 array that allows a facile electron-transfer between B and B', Bn++B’m+↔B(n+1)++B’(m-1)+ without an energy cost, just as occurs in ReO3 and other metallic ABO3 perovskites. In an effort to understand the Cu-O-M (M = Ti, Mn, Fe, Ru) electronic interaction in two dimension, we have investigated K2N1F4 oxides of the general formula La2-2xSr2XCui.xMxO4 (M = Ti, Mn, Fe or Ru). These investigations are described in Chapter 4. For M = Ti, only the x = 0.5 member could be prepared, while for M = Mn and Fe, the composition range is 0 < x < 1.0, and for M = Ru, the composition range is 0 < x ≤ 0.5. There is no evidence for ordering of Cu(II) and M(IV) in the x = 0.5 members. While the members of the M = Ti, Mn and Ru series are semiconducting/insulating, the members of the M = Fe series are metallic, showing a broad metal-semiconductor transition around 100 K for 0 < x ≤ 0.15 that is possibly related to a Cu(II)-O-Fe(IV) < > Cu(III)-O-Fe(III) valence degeneracy. Increasing the strontium content at the expense of lanthanum in La2-2xSr2XCui.xFexO4 for x ≤ 0.20 renders the samples metallic but not superconducting. In a search for inorganic oxide materials showing second order nonlinear optical (NLO) susceptibility, we have investigated several borates, silicates and phosphates containing /ram-connected MO6 octahedral chains or MO5 square-pyramids, where M = d°: Ti(IV), Nb(V) or Ta(V). Our investigations, which are described in Chapter 5, have identified two new NLO structures: batisite, Na2Ba(TiO)2Si4O12, containing trans-connectd TiO6 octahedral chains, and fresnoite, Ba2TiOSi2O7, containing square-pyramidal T1O5. Investigation of two other materials containing square-pyramidal TiO5, viz., Cs2TiOP2O7 and Na4Ti2Si8O22. 4H2O, revealed that isolated TiO5 square-pyramids alone do not cause a second harmonic generation (SHG) response; rather, the orientation of T1O5 units to produce -Ti-O-Ti-O- chains with alternating long and short Ti-0 distances in the fresnoite structure is most likely the origin of a strong SHG response in fresnoite. Indeed, we have been able to prepare a new fresnoite type oxide, Ba2.xVOSi2O7 (x ~ 0.5) that shows a strong SHG response, confirming this hypothesis. In the Appendix, we have described three synthetic strategies that enabled us to prepare magnetic and NLO materials. We have shown that the reaction CrO3 + 2 NH4X > CrO2 + 2 NH3 + H2O + X2 (X = Br, I), which occurs quantitatively at 120-150 °C, provides a convenient method for the synthesis of CrO2. Unlike conventional methods, the method described here does not require the use of high pressure for the synthesis of this technologically important material. For the synthesis of magnetic double perovskites, we have developed a method that involves reaction of basic alkali metal carbonates with the acidic oxides (e.g. Re2O7) first, followed by reaction of this precursor oxide with the required transition metal/transition metal oxide (e.g. Fe/Fe2O3). By this method we have successfully prepared single-phase perovskite oxides, A2FeReO6, ACrMoO6 and ALaFeVO6. We have prepared the new NLO material Ba2_xV0Si207 from Ba2VOSi2O7 by a soft chemical redox reaction involving the oxidation of V(IV) to V(V) using Br2 in CH3CN/CHCI3. Ba2V0Si207 + 1/2 Br2 > Bai.5V0Si207 + 1/2 BaBr2. The work presented in this thesis was carried out by the candidate as part of the Ph.D. training programme. He hopes that the studies reported here will constitute a worthwhile contribution to the solid state chemistry of transition metal oxides and related materials.

Transition metal compounds, especially the oxides, containing dn (0 ≤ n ≤ 10) electronic configuration, constitute the backbone of solid state/materials chemistry aimed at realization of novel materials properties of technological importance. Some of the significant materials properties of current interest are spin-polarized metallic ferromagnetism, negative thermal expansion, second harmonic nonlinear optical (NLO) susceptibility, fast ionic and mixed electronic/ionic conductivity for application in solid state batteries, and last but not the least, high-temperature superconductivity. Typical examples for each one of these properties could be found among transition metal oxides. Thus, alkaline-earth metal (A) substituted rare-earth (Ln) manganites, Lnı.xAxMnΟ3, are currently important examples for spin-polarized magnetotransport, ZrV2O7 and ZrW2O8 for negative thermal expansion coefficient, KTiOPO4 and LiNbO3 for second harmonic NLO susceptibility, (Li, La) TiO3 and LiMn2O4 for fast-ionic and mixed electronic/ionic conductivity respectively, and the whole host of cuprates typified by YBa2Cu3O7 for high Tc superconductivity. Solid state chemists constantly endeavour to obtain structure-property relations of solids so as to be able to design better materials towards desired properties. Synthesis coupled with characterization of structure and measurement of relevant properties is a common strategy that chemists adopt for this task. The work described in this thesis is based on such a broad-based chemists' approach towards understanding and realization of novel materials properties among the family of metal oxides. A search for metallic ferro/ferrimagnetism among the transition metal perovskite oxides, metallicity and possibility of superconductivity among transition-metal substituted cuprates and second order NLO susceptibility among metal oxides containing d° cations such as Ti(IV), V(V) and Nb(V) - constitute the main focus of the present thesis. New synthetic strategies that combine the conventional ceramic approach with the chemistry-based 'soft1 methods have been employed wherever possible to prepare the materials. The structures and electronic properties of the new materials have been probed by state-of-the art techniques that include powder X-ray diffraction (XRD) together with Rietveld refinement, electron diffraction, thermogravimetry, measurement of magnetic susceptibility (including magnetoresistance), Mossbauer spectroscopy and SHG response (towards 1064 nm laser radiation), besides conventional analytical techniques for determination of chemical compositions. Some of the highlights of the present thesis are: (i) synthesis of new mixed valent [Mn(III)/Mn(IV)] perovskite-type manganites, ALaMn2O6-y (A = K, Rb) and ALaBMn3O9_y (A = Na, K; B = Ca, Sr) that exhibit ferromagnetism and magnetoresistance; (ii) investigation of a variety of ferrimagnetic double-perovskites that include ALaMnRuO6 (A = Ca, Sr, Ba) and ALaFeVO6 (A = Ca, Sr) and A2FeReO6 (A = Ca, Sr, Ba) providing new insights into the occurrence of metallic and nonmetallic ferrimagnetic behaviour among this family of oxides; (iii) synthesis of new K2NiF4-type oxides, La2-2xSr2XCui.xMxO4 (M = Ti, Mn, Fe, Ru) and investigation of Cu-O-M interaction in two dimension and (iv) identification of the structural rnotif(s) that gives rise to efficient second order NLO optical (SHG) response among d° oxides containing Ti(IV), V(V), Nb(V) etc., and synthesis of a new SHG material, Ba2-xVOSi2O7 having the fresnoite structure. The thesis consists of five chapters and an appendix, describing the results of the investigations carried out by the candidate. A brief introduction to transition metaloxides, perovskite oxides in particular, is presented in Chapter 1. Attention is focused on the structure and properties of these materials. Chapter 2 describes the synthesis and investigation of two series of anion-deficient perovskite oxides, ALaMn2O6-y (A = K, Rb, Cs) and ALaBMn3O9_y (A = Na, K; B = Ca, Sr). ALaMn2O6-y (A = K, Rb, Cs) series of oxides adopt 2 ap x 2 ap superstructure for K and Rb phases and √2 av x √2 ap x 2 ap superstructure (ap = perovskite subcell) for the Cs phase. Among ALaBMn3O9-y phases, the A = Na members adopt a new kind of perovskite superstructure, ap x 3 ap, while the A = K phases do not reveal an obvious superstructure of the perovskite. All these oxides are ferromagnetic (Tc ~ 260-325 K) and metallic exhibiting a giant magnetoresistance behaviour similar to alkaline earth metal substituted lanthanum manganites, Lai_xAxMnO3. However, unlike the latter, the resistivity peak temperature Tp for all the anion-deficient manganites is significantly lower than Tc. In Chapter 3, we have investigated structure and electronic properties of double-perovskite oxides, A2FeReO6 (A = Ca, Sr and Ba). The A = Sr, Ba phases are cubic (Fm3m) and metallic, while the A = Ca phase is monoclinic (P2yn) and nonmetallic. All the three oxides are ferrimagnetic with Tcs 315-385 K as reported earlier. A = Sr, Ba phases show a negative magnetoresistance (MR) (10-25 % at 5 T), while the Ca member does not show an MR effect. 57Fe Mossbauer spectroscopy shows that iron is present in the high-spin Fe3+ (S = 5/2) state in Ca compound, while it occurs in an intermediate state between high-spin Fe2+ and Fe3+ in the Ba compound. Monoclinic distortion and high covalency of Ca-O bonds appear to freeze the oxidation states at Fe+3/Re5+ in Ca2FeRe O6, while the symmetric structure and ionic Ba-O bonds render the FeReO6 array highly covalent and Ba2FeReO6 metallic. Mossbauer data for Sr2FeReO6 shows that the valence state of iron in this compound is intermediate between that in Ba and Ca compounds. It is likely that Sr2FeReO6 which lies at the boundary between metallic and insulating states is metastable, phase-seperating into a percolating mixture of different electronic states at the microscopic level. In an effort to understand the occurrence of metallicity and ferrimagnetism among double perovskites, we have synthesized several new members : ALaMnFeO6 (A = Ca, Sr, Ba), ALaMnRuO6 (A = Ca, Sr, Ba) and ALaVFeO6 (A = Ca, Sr) (Chapter 3). Electron diffraction reveals an ordering of Mn and Ru in ALaMnRuO6 showing a doubling of the primitive cubic perovskite cell, while ALaVFeO6 do not show an ordering. ALaMnRuOs are ferrimagnetic (Tcs ~ 200-250 K) semiconductors, but ALaVFeO6 oxides do not show a long range magnetic ordering . The present work together with the previous work on double perovskites shows that only a very few of them exhibit both metallicity and ferrimagnetism, although several of them are ferrimagnetic. For example, among the series Ba2MReO6 (M = Mn, Fe, Co, Ni), only the M = Fe oxide is both metallic and ferrimagnetic, while M = Mn and Ni oxides are ferrimagnetic semiconductors. Similarly, A2CrMoO6 (A = Ca, Sr), A2CrRe06 (A = Ca, Sr), and ALaMnRuO6 (A = Ca, Sr, Ba) are all ferrimagnetic but not metallic. While ferrimagnetism of double perovskites arise from an antiferromagnetic coupling of B and B' spins through the B-O-B' bridges, the occurrence of metallicity seems to require precise matching of the energies of d-states of B and B' cations and a high covalency in the BB'O6 array that allows a facile electron-transfer between B and B', Bn++B’m+↔B(n+1)++B’(m-1)+ without an energy cost, just as occurs in ReO3 and other metallic ABO3 perovskites. In an effort to understand the Cu-O-M (M = Ti, Mn, Fe, Ru) electronic interaction in two dimension, we have investigated K2N1F4 oxides of the general formula La2-2xSr2XCui.xMxO4 (M = Ti, Mn, Fe or Ru). These investigations are described in Chapter 4. For M = Ti, only the x = 0.5 member could be prepared, while for M = Mn and Fe, the composition range is 0 < x < 1.0, and for M = Ru, the composition range is 0 < x ≤ 0.5. There is no evidence for ordering of Cu(II) and M(IV) in the x = 0.5 members. While the members of the M = Ti, Mn and Ru series are semiconducting/insulating, the members of the M = Fe series are metallic, showing a broad metal-semiconductor transition around 100 K for 0 < x ≤ 0.15 that is possibly related to a Cu(II)-O-Fe(IV) < > Cu(III)-O-Fe(III) valence degeneracy. Increasing the strontium content at the expense of lanthanum in La2-2xSr2XCui.xFexO4 for x ≤ 0.20 renders the samples metallic but not superconducting. In a search for inorganic oxide materials showing second order nonlinear optical (NLO) susceptibility, we have investigated several borates, silicates and phosphates containing /ram-connected MO6 octahedral chains or MO5 square-pyramids, where M = d°: Ti(IV), Nb(V) or Ta(V). Our investigations, which are described in Chapter 5, have identified two new NLO structures: batisite, Na2Ba(TiO)2Si4O12, containing trans-connectd TiO6 octahedral chains, and fresnoite, Ba2TiOSi2O7, containing square-pyramidal T1O5. Investigation of two other materials containing square-pyramidal TiO5, viz., Cs2TiOP2O7 and Na4Ti2Si8O22. 4H2O, revealed that isolated TiO5 square-pyramids alone do not cause a second harmonic generation (SHG) response; rather, the orientation of T1O5 units to produce -Ti-O-Ti-O- chains with alternating long and short Ti-0 distances in the fresnoite structure is most likely the origin of a strong SHG response in fresnoite. Indeed, we have been able to prepare a new fresnoite type oxide, Ba2.xVOSi2O7 (x ~ 0.5) that shows a strong SHG response, confirming this hypothesis. In the Appendix, we have described three synthetic strategies that enabled us to prepare magnetic and NLO materials. We have shown that the reaction CrO3 + 2 NH4X > CrO2 + 2 NH3 + H2O + X2 (X = Br, I), which occurs quantitatively at 120-150 °C, provides a convenient method for the synthesis of CrO2. Unlike conventional methods, the method described here does not require the use of high pressure for the synthesis of this technologically important material. For the synthesis of magnetic double perovskites, we have developed a method that involves reaction of basic alkali metal carbonates with the acidic oxides (e.g. Re2O7) first, followed by reaction of this precursor oxide with the required transition metal/transition metal oxide (e.g. Fe/Fe2O3). By this method we have successfully prepared single-phase perovskite oxides, A2FeReO6, ACrMoO6 and ALaFeVO6. We have prepared the new NLO material Ba2_xV0Si207 from Ba2VOSi2O7 by a soft chemical redox reaction involving the oxidation of V(IV) to V(V) using Br2 in CH3CN/CHCI3. Ba2V0Si207 + 1/2 Br2 > Bai.5V0Si207 + 1/2 BaBr2. The work presented in this thesis was carried out by the candidate as part of the Ph.D. training programme. He hopes that the studies reported here will constitute a worthwhile contribution to the solid state chemistry of transition metal oxides and related materials.

This study critically investigates the material and structural behaviour of Aer-Tech material. Aer- Tech material is composed of 10% by volume of foam mechanically entrapped in a plastic mortar. The research study showed that the density of the material mix controls all other properties such as fresh state properties, mechanical properties, functional properties and acoustic properties. Appreciably, the research had confirmed that Aer-Tech material despite being classified as a light weight material had given high compressive strength of about 33.91N/mm2. The compressive strength characteristics of Aer-Tech material make the material a potential cost effective construction material, comparable to conventional concrete. The material also showed through this study that it is a structural effective material with its singly reinforced beam giving ultimate moment of about 38.7KN. In addition, the Aer-Tech material is seen as a very good ductile material since, the singly reinforced beam in tension showed visible signs of diagonal vertical cracks long before impending rapture. Consequently, the SEM test and the neural network model predictions, carried out had showed how billions of closely tight air cells are evenly distributed within the Aer-Tech void system as well as the close prediction of NN model for compressive strength and density are same with the experimental results of compressive strength and density. The result shows that the Aer-Tech NN-model can simulate inputs data and predicts their corresponding output data.

Multiferroic materials exhibit simultaneously, magnetic and electric order. In a magnetoelectric composite structure, a coupling is induced via an interfacial elastic interaction between magnetostrictive and piezoelectric materials enabling the control of the magnetisation by applying an electric field and vice versa. However, despite the potential of such coupling, experimental limits of theoretical models were observed. This work sheds some light on these limits by focusing the research on the chemistry of nanocomposite CoFe2O4 and BaTiO3, particularly at the interfaces where the coupling predominates. A comparison of the most common conductive oxides, Nb doped SrTiO3 and SrRuO3, was made for the bottom electrode application. The variation of conductive properties in Nb-SrTiO3 thin films at high temperature has been quantified when artificially strained and 60 nm SrRuO3 film was found to be the best bottom electrode choice for room temperature use. Epitaxial growth of magnetic CoFe2O4 was achieved on various metal oxide substrates despite large lattice mismatches. Crystallographic properties and strain evaluation were investigated and a Stranski-Krastanov growth mechanism, arising from the PLD deposition, was predominant. A notable drop of magnetisation was observed depending on the growth template, particularly on BaTiO3 substrates, the piezoelectric counterpart of the magnetoelectric structures. However, an encouraging magnetoelectric coupling induced by thermal phase transition of BaTiO3 was revealed. For BaTiO3, a control of the growth direction was realised by varying the deposition pressure, and the existence of both 180° and 90° ferroelectric domains was observed for films up to 300 nm in thickness. However, both the ferroelectric and piezoelectric properties were reduced in the thin films due to the clamping effect of the substrate. Finally, highly crystalline multilayers of CoFe2O4 and BaTiO3 were prepared on SrRuO3 buffered SrTiO3 substrates. It was found that the degradation of both magnetic and ferroelectric properties was proportional to the increase in the number of interfaces. A thorough microscopic study revealed interdiffusion and chemical instability occurring between CoFe2O4 and BaTiO3 at the interface. This undesired effect was partially recovered by the insertion of an ultra thin layer of SrTiO3, acting as a barrier layer at every interface. This research shows how interfacial chemistry need to be understood to achieve high magnetoelectric coupling in these types of epitaxial engineered structures.

The structural, thermal and thermodynamic properties of some Ln-Pd oxides of the Ln4Pd07 type are presented. The main results are; (i) Reduction of Ln4Pd07, either ex-situ by CO or in-situ by a synthetic car exhaust gas, results in a materialwith catalytic activity for car exhaust gas clean-up reactions. The obtained material consists of Pd nanoparticles situated on the surface of micron-sized grains of Ln2O3 Upon heat treatment of the reduced material in air, Lu4Pd07 i srapidly re-formed. This property May be utilised for reactivation/conditioning of aged Ln4Pd07-based catalysts; (ii) The Ln4Pd07 compounds with Ln = Nd, Sm, Eu and Gd dare isostructural and have a structure which is a triclinic distortion of the monoclinic La4Pd07 type; (iii) ΔH°, and ΔS ° f values for La4Pd07 and Nd4Pd07 have been calculated by a combination of data obtained from dissolution calorimetry and thermogravimetric analysis studies; ( iv ) Carbon nanotubes, having the so-called fishbone structure, can be prepared by heat treatment o f La4Pd07 in a 20% CO/He gas mixture for an extended period of time. Nanotubes have been extracted from the obtained La203/Pd/nanotube mixture, using a wet-chemical method.

Härtill 5 uppsatser

Metal oxide nanoparticles, both magnetic and nonmagnetic, have a multitude of applications in gas sensors, catalysts and catalyst supports, airborne trapping agents, biomedicines and drug delivery systems, fuel cells, laser diodes, and magnetic microwaves. Over the past decade, an inexpensive, simple, recyclable, and environmentally friendly large, scale synthesis method for the synthesis of these metal oxide nanoparticles has been sought. Many of the current techniques in use today, while good on the small, laboratory bench scale, suffer from drawbacks that make them unsuitable for the industrial scale. The aminolytic method, developed by Dr. Man Han while working for Dr. Zhang, fits industrial scale-up requirements. The aminolytic method involves a reaction between metal carboxylate(s) and oleylamine in a non-coordinating solvent. This system was shown to produce a range of spinel ferrites. Dr. Lisa Vaughan showed that this method can be recycled multiple times without degrading the quality of the produced nanoparticles. The purpose of this thesis is to test the versatility of the aminolytic method in the production of a wide range of metal oxides as well as various core/shell systems. Chapter 2 explores the effect of precursor carboxylates chain length on the aminolytic synthesis of cobalt ferrite, and manganese ferrite nanoparticles. In Chapter 3, a series of CuxMn1-xFe₂O₄, (x ranges from 0.0 to 0.2), nanoparticles were synthesized via the aminolytic method. This series allows for the investigation of the effects of orbital Jahn-Teller distortion as well as orbital angular momentum on the magnetic properties of this ferrite. The quantum couplings of magnetic ions in spinel ferrites govern their magnetic properties and responses. An understanding of the couplings between these metal ions allows for tailoring magnetic properties to obtain the desired response needed for various applications. Chapter 4 investigates the synthesis of MnO and Mn₃O₄ nanoparticles in pure single phase with high monodispersity. To the best of our knowledge, the range of sizes produced for MnO and Mn₃O₄ is the most extensive, and therefore a magnetic study of these systems shows some intriguing size dependent properties. The final part of this chapter investigates the applicability of the aminolytic method for building a MnO shell on a CoFe₂O₄ core. Chapter 5 explores the synthesis of another metal oxide, ZrO₂ in both the cubic and monoclinic phases with no impurities. The use of the aminolytic method here removes the need for dangerous/expensive precursors or equipment and eliminates the need for extensive high temperature heat treatments that destroy monodispersity which is required for most techniques. The creation of a core/shell system between CoFe₂O₄ and ZrO₂ using the aminolytic method was also tested. This core/shell system adds magnetic manipulation which is especially useful for the recovery of zirconia based photocatalyst. Chapter 6 studies the application of the aminolytic method in the synthesis of yttrium iron garnet (YIG) and yttrium iron perovskite (YIP) nanoparticles. Current synthesis techniques used to produce YIG and YIP nanoparticles often requires high temperatures, sensitive to contamination, which could be eliminated through the use of our method

Surfaces of metal oxides play a vital role in many technologically important applications. The surfaces of titanium dioxide, in particular, show quite promising properties that can be utilized in solid-state gas sensing and photocatalysis applications. In the first part of this dissertation we investigate these properties of TiO2 surfaces through a vigorous surface scientific approach. In the second part, we investigate the possibilities of modifying the TiO2 surfaces by depositing multi-component transition metal oxide monolayers so that the properties of bare TiO2 surface can be influenced in a beneficial way. For instance, via formation of new surface sites or cations that have different valance states, the chemisorption and catalytic properties can be modified. We use sophisticated experimental surface science techniques that are compatible with ultra-high vacuum technology for surface characterization. All the experimental results, except for the photocatalysis experiments, were compared to and verified by supporting DFT-based theoretical results produced by our theory collaborators. TiO2 based solid-state gas sensors have been used before for detecting trace amounts of explosives such as 2,4-dinitrololuene (DNT), a toxic decomposition product of the explosive 2,4,6-trinitrotoluene (TNT) that have very low vapor pressure. However, the adsorption, desorption and reaction mechanism were not well- understood. Here, we investigate 2,4-DNT adsorption on rutile-TiO2(110) surface in order to gain insight about these mechanisms in an atomistic level and we propose an efficient way of desorbing DNT from the surface through UV-light induced photoreactions. TiO2 exists in different polymorphs and the photocatalytic activity differs from one polymorph to another. Rutile and anatase are the most famous forms of TiO2 in photocatalysis and anatase is known to show higher activity than rutile. The photoactivity also varies depending on the surface orientation for the same polymorph. So far, a reasonable explanation as to why these differences exist was not reported. In our studies, we used high quality epitaxial rutile and anatase thin films which enabled isolating the surface effects from the bulk effects and show that it is the difference between the charge carrier diffusion lengths that causes this difference in activities. In addition to that, using different surface orientations of rutile-TiO2, we show that the anisotropic bulk charge carrier mobility may contribute to the orientation dependent photoactivity. Moreover, we show that different surface preparation methods also affect the activity of the sample and vacuum reduction results in an enhanced activity. In an effort to modify the TiO2 surfaces with monolayer/mixed monolayer oxides, we carried out experiments on (011) orientation of single crystal rutile TiO2 with few of the selected transition metal oxides namely Fe, V, Cr and Ni. We found that for specific oxidation conditions a monolayer mixed oxide is formed for all M (M= Fe, V, Cr, Ni), with one common structure with the composition MTi2O5. For small amounts of M the surface segregates into pure TiO2(011)-2×1 and into domains of MTi2O5indicating that this mixed monolayer oxide is a low energy line phase in a compositional surface phase diagram. The oxygen pressure required for the formation of this unique monolayer structure increases in the order of V2O5 mixed monolayer oxide by DFT-based simulations was verified by X-ray photoemission diffraction measurements performed at a synchrotron facility.

Examining the phenotypic variation observed within a species is an opportunity to understand the evolutionary stability and potential evolutionary trajectories of the species. Feather coloration in many birds is produced by complex biochemical networks that modify ingested, dietary carotenoids to produce colorful carotenoids deposited into feathers. Within-species color variation can be caused by variation in either the structure of this network or the flux through it. Here we tested the contribution of structural properties of biochemical networks to variation across individuals from 21 populations of house finches (Haemorphous mexicanus) in recently established populations in Montana and ancestral populations in Arizona. With the largest carotenoid networks of any studied species, the house finch provides an ideal system to address how population-specific utilization of biochemical networks contributes to population divergence in coloration. Using high performance liquid chromatography, we extracted and identified the carotenoid compounds from over 3,000 feather samples representing 1,000 individuals. We analyzed the relationship between the presence of different compounds across populations and their topological positions within the network. We then tested whether populations diverge along the same or different pathways within the network. We found that derived carotenoids contributed more to population divergence compared to dietary carotenoids, suggesting that evolution of biochemical synthesis accompanied recent population divergence in ecologically distinct locations.

En los últimos años ha habido un interés creciente en el estudio de el compuesto La2NiO4+?, debido a sus propiedades como conductor mixto iónico-electrónico, que lo hacen adecuado para su utilización en dispositivos electroquímicos, tales como cátodo para pilas de combustible de óxido sólido a temperaturas intermedias (IT-SOFC), membranas de permeación o sensores de gas. La estructura de fase La2NiO4+? está formada por láminas de LaNiO3, de tipo perovskita, alternadas con láminas de LaO de tipo cloruro sódico, en las cuales puede incorporarse oxígeno sobreestequiométrico. Esta estructura laminar es la responsable de la anisotropía en las propiedades del La2NiO4+?, dando lugar a una conductividad iónica y electrónica que es entre dos y tres órdenes de magnitud superior a lo largo del plano ab, en comparación con la dirección del eje c.
Este trabajo consiste en el estudio, desde un punto de vista fundamental, de películas delgadas epitaxiales de La2NiO4+? orientadas a lo largo del eje c y crecidas por la técnica de deposición química en fase vapor de precursores organometálicos por inyección pulsada (PI-MOCVD) sobre diferentes sustratos, con el fin de adquirir una mejor comprensión de sus características microestructurales, su variación con la tensión y la influencia de la tensión en las propiedades de transporte a elevada temperatura. Además, el crecimiento epitaxial permite la medida de las propiedades de las películas de La2NiO4+? en dos direcciones perpendiculares, obteniendo una medida directa de la anisotropía del material.
El La2NiO4+? es el primer miembro (n = 1) de la familia Ruddlesden-Popper Lan+1NinO3n+1, en la que la estructura de cada miembro está formada por un número n de bloques perovskita LaNiO3 alternados entre bloques LaO tipo cloruro sódico. Asimismo se han intentado depositar películas orientadas a lo largo del eje c de los miembros n = 2, 3 e ?, y se ha estudiado la variación las propiedades de transporte a lo largo de la serie Lan+1NinO3n+1.
En la tesis se realiza una introducción a los conductores mixtos iónicos-electrónicos (MIEC) y a los cátodos para pilas de combustible de óxido sólido (SOFC), como una posible aplicación del material La2NiO4+?. Se describen las propiedades más importantes de la fase La2NiO4+?, y de los miembros n =2, 3 e ? de la familia Lan+1NinO3n+1, así como el estado del arte de la preparación de películas delgadas de estos materiales.
A continuación se describe la técnica de deposición química en fase vapor de precursores organometálicos por inyección pulsada (PI-MOCVD), acompañada de una descripción detallada de los parámetros de depósito seleccionados, y del equipo PI-MOCVD utilizado. También se describen las técnicas utilizadas en la caracterización de las películas delgadas de Lan+1NinO3n+1.
Posteriormente se describen los parámetros de depósito optimizados para la deposición de películas epitaxiales de La2NiO4+? y se realiza una caracterización estructural, morfológica y microestructural en función del espesor de las películas, del sustrato utilizado y de la temperatura. También se detalla y describe la conductividad total de películas epitaxiales de diferente espesor medida. Para éstas películas se han medido, además, las propiedades de intercambio y de difusión de oxígeno utilizando dos técnicas diferentes: la técnica de intercambio de isótopos y la técnica de relajación de la conductividad. Los resultados de estas medidas se discuten en función de la microestructura de las películas.
Por último, se ha completado el estudio describiendo los primeros resultados de deposición de otros miembros de la familia Ruddlesden-Popper. La evolución de las propiedades de transporte total de las películas delgadas de Lan+1NinO3n+1 se han relacionado con el número de láminas tipo perovskita n.
In the last years there has been a great interest in the study of the La2NiO4+? compound due to its mixed ionic-electronic properties, which make it suitable in electrochemical devices, such as cathode in Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC), permeation membranes or gas sensors. The La2NiO4+? phase structure is formed by perovskite-type LaNiO3 layers alternated with rocksalt-type LaO layers, in which hyperstoichiometric oxygen can be incorporated. This layered structure is responsible for the anisotropy in the La2NiO4+? properties, leading to electronic and ionic conductivity three orders of magnitude higher along the ab plane, in comparison with the c-axis direction.
This work is focused on the study, from a fundamental point of view, of epitaxial c-axis oriented La2NiO4+? thin films deposited by PI-MOCVD technique on different substrates, in order to achieve a better comprehension of the microstructural characteristics, their variation with strain and their influence in its high temperature transport properties. Moreover, the epitaxial growth of the films permits the measurement of the properties of the La2NiO4+? in two perpendicular directions, to have a direct inset of the anisotropy.
The La2NiO4+? phase is the n = 1 member of the Lan+1NinO3n+1 Ruddlesden-Popper family, in which the structure of each member is formed by a n number of perovskite layers alternated between rock-salt layers. We have also attempted to deposit c-axis oriented films of the n = 2, n = 3 and n = 1 members and studied the variation of the transport properties through the different members of the family.
First, Chapter 1 consists of an introduction to the mixed ionic-electronic conductors (MIEC) and to the solid oxide fuel cell (SOFC) cathodes, as a possible application of the La2NiO4+? material. The most remarkable properties of the La2NiO4+? phase, and of the n = 2, 3 and 1 members of the Lan+1NinO3n+1 family are analyzed, as well as the state of the art in the preparation of thin films of these materials.
In Chapter 2, the Metalorganic Chemical Vapor Deposition (MOCVD) technique is described, accompanied by a detailed description of the selected experimental deposition parameters and of the Pulsed Injection MOCVD equipment used. Chapter 3 summarizes all the techniques used for the Lan+1NinO3n+1 thin film characterization.
In Chapter 4, the optimized experimental parameters for the deposition of epitaxial La2NiO4+? thin films are described. Structural, morphological and microstructural characterization is performed as a function of film thickness, substrate used and temperature. Total conductivity of epitaxial layers is also described and discussed.
In Chapter 5 we have studied the oxygen exchange and transport of the La2NiO4+? thin films by two different techniques: the oxygen isotope exchange and the electrical conductivity relaxation. Results are discussed as a function of microstructure.
Finally, in Chapter 6, the study is completed describing the first results of the deposition of the other members of the Ruddlesden-Popper family. Evolution of the total conductivity properties of the Lan+1NinO3n+1 films has been related to the n number of perovskite layers.

MnOx-CeO2 catalysts (molar ratio Mn/Ce 1) were prepared using two methods: co-precipitation and citrate methods. The prepared solids were calcined at 500°C, and characterized by XRD, nitrogen adsorp-tion-desorption technique and SEM morphological, they were, then, tested in the toluene combustion reac-tion. The catalytic performances of the prepared solids were evaluated in the temperature range 150-400°C. The XRD analysis of the two solids showed that the only crystalline phase detected is cerium oxide. BET surface area measurements showed that the incorporation of manganese led to an increase in the spe-cific surface area of ceria, the solid prepared by the co-precipitation method led to the highest specific sur-face area (156 m²/g). The solids showed good performances in the toluene combustion reaction that depend strongly on the preparation method. The best catalytic activity was obtained for the catalyst prepared by the citrate method achieving a complete conversion of toluene at 250 ° C. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35257

Indium-tin oxide (ITO) is commonly used as the transparent electrode in organic photovoltaic (OPV) devices. ITO's transparent properties come at the expense of less than ideal electrode characteristics arising from insulating over-oxidized surface species. OPVs fabricated on the native ITO surface tend to exhibit poor performance with a high degree of variability from device to device. Aggressive acid etching of the ITO surface removes the majority of the insulating surface species leading to improvements in OPV efficiency with greater reproducibility and increased device to device consistency.Organic light emitting diodes (OLEDs) are planar electroluminescent light sources that naturally couple a portion of their emission into internally reflected modes within the device substrate. Although this coupling property is well known, few attempts have been made to integrate OLEDs as light sources for internal reflection elements. Furthermore, OPVs share the optical coupling properties of OLEDs and therefore can be used as integrated internal reflection detectors. Integrating both an OLED light source and an OPV detector onto the same substrate results in an internal reflection sensing platform that requires no free-space optics, has low power consumption requirements, and can be easily fabricated on substrates occupying an area less than one square inch. In this work we establish a functional prototype design, characterize the fundamental coupling properties, and demonstrate several surface sensing responses of this fully integrated optical sensing platform.The net solar power production from OPVs arises from the interactions between multiple currents through the device. The photocurrent is the only power producing current in the device and understanding the voltage dependent nature of this current is essential in OPV research. Analysis methods of conventional, inorganic photovoltaics do not adequately describe the photocurrent behavior commonly observed in OPVs. OPV analysis is therefore somewhat limited by the methods commonly employed. To improve upon the convention methods we develop a simplified method of OPV photocurrent analysis based on electrochemical methods that accurately describes the voltage dependence of the photocurrent and leads to greater insight into the key parameters involved in solar power production from OPVs.

Under the ever-increasing requirements of higher power and higher radio-frequency in future power electronics and telecommunication applications, the thermal management of gallium nitride (GaN) based devices becomes crucial, this can be significantly improved by integrating high thermal conductivity diamond into the devices to enhance the extraction of waste heat. An important consideration is the thermal boundary resistance (TBR) of the GaN/diamond interface, which forms a bottleneck for heat transport. For incorporation as a substrate, the thermal properties of this interface and of the polycrystalline diamond (PCD) grown onto GaN using various controlled barrier layers under different growth conditions are investigated and systematically compared; SiN barrier layers were found normally producing lower TBR with a smoother interface formed. For integration of PCD as a top-side heat spreader onto AlGaN/GaN-on-Si HEMT, its thermal performance was systematically evaluated by time-domain thermoreflectance and ANSYS simulation; at best a 15% reduction in peak temperature was obtained when only the source-drain opening of a passivated AlGaN/GaN-on-Si HEMT is overgrown with PCD. Meanwhile, next generation higher compacted electronics for future communications or computing require sub-10-nm or even atomic dimension scaling, incorporation of a new two-dimensional (2D) materials channel then has emerged as a highly attractive solution to address this challenge. Gallium telluride (GaTe) is a 2D layered material that recently raised considerable interests due to its unique optoelectronic properties but is still under extensive exploration of its fundamental properties for potential applications. The pressure-dependent solid-state properties of GaTe multilayers up to 46 GPa were firstly investigated. A strong Raman mode anisotropic splitting started at ~6.5 GPa originating from phase transition was first-time revealed and understood through first-principles calculations. Then the thermal properties of free-standing GaTe multilayers were studied mainly by micro-Raman opto-thermography, displaying an anisotropic and very low thermal conductivities along the in-plane armchair and zigzag orientations. Moreover, the mechanical properties of both SiO2/Si substrates supported and free-standing GaTe multilayers were investigated mainly through nanoindentation. Concurrence of multiple pop-ins and load-drops in the loading curve were found, likely originating from interlayer sliding within the GaTe multilayer. These pressure-tuned behaviors, thermal and mechanical properties of GaTe multilayers enable new insights for investigating and manipulating the anisotropic solid-state properties of potential device applications and other low symmetry layered materials.

This thesis investigates the electrochromic NixW1-x oxide thin film system, where 0 < x < 1. The thin films were deposited by reactive DC magnetron co-sputtering from one Ni and one W metal target. In addition, Ni oxide was deposited with water vapor added to the sputtering gas. The different compositions were structurally characterized by X-ray diffraction, X-ray photoelectron-, Rutherford backscattering- and Raman spectroscopy. Possible nanostructures were studied by ellipsometry together with effective medium theory. Optical and electrochemical properties were investigated by spectrophotometry and cyclic voltammetry in 1 M lithium perchlorate in propylene carbonate (Li-PC). Li-PC electrolyte was used as it is being compatible with both W and Ni oxides. Few studies have previously been made on Ni oxides in Li-PC. Films with high Ni content, 0.85 < x < 1, were polycrystalline and all other films were amorphous. W-rich films, x < 0.5, consisted of a mixture of W oxide and NiWO4 -phases, and the Ni-rich samples, x > 0.5, probably consisted of hydrated Ni oxide and NiWO4 -phases. Films with 0 < x < 0.3 showed electrochromic properties similar to W oxide, and films with 0.7 < x < 1 behaved as Ni oxide. For 0.4 < x < 0.7 no optical change was seen. At the border of cathodic electrochromic and non-electrochromic behavior, i.e. x ~ 0.4, the sample behaved as an optically passive intercalation material. The transmittance change was 0.45 and 0.15 for the W-rich and Ni-rich films, respectively. Ni addition to W oxide improved the coloration efficiency. For the Ni-rich films the charge insertion/extraction and optical modulation was low and an aging effect resulted in strong bleaching of the samples. The advantage of W addition to Ni oxide was that the transparency at the bleached state was enhanced. Moreover, it was found that the hydrous character of the Ni oxide had a large impact on the electrochromic performance, both when electrochemically cycled in KOH and in the non-aqueous Li-PC.

Die untersuchten Ferekristalle sind neuartige Verwachsungs-Schichtverbindungen aus m Monolagen von Niobdiselenid (NbSe2), die wiederholt mit n atomaren Bilagen von Bleiselenid (PbSe) oder Zinnselenid (SnSe) geschichtet sind. Niobdiselenid als Volumenmaterial besitzt eine Schichtstruktur und ist ein Supraleiter. Aufgrund ihrer gezielt einstellbaren atomar geschichteten Struktur können Ferekristalle als Modellsysteme für geschichtete Supraleiter dienen. In dieser Arbeit werden ihre strukturellen und elektrischen Eigenschaften untersucht. Mittels Transmissionselektronenmikroskopie wird ihre turbostratisch ungeordnete, nanokristalline Struktur nachgewiesen. Die atomare Struktur innerhalb der einzelnen Schichten ist ähnlich wie in den Volumenmaterialien NbSe2, PbSe und SnSe, wobei die kristallographischen c-Achsen parallel zur Stapelrichtung der Ferekristalle zeigen. Eine quantitative Analyse unter Verwendung eines Zwei-Schicht-Modells für den spezifischen Widerstand, Hall-Koeffizienten und Magnetwiderstand liefert ähnliche Ladungsträgersorten, -dichten und –beweglichkeiten in den NbSe2-Schichten, wie sie für isolierte Einzellagen von NbSe2 berichtet wurden. Diese unterscheiden sich von denen des Volumenmaterials NbSe2. Erstmals wurde ein Übergang der Ferekristalle in den supraleitenden Zustand nachgewiesen. Die Sprungtemperaturen sind dabei in etwa auf die Hälfte der Sprungtemperaturen der jeweiligen nicht turbostratisch ungeordneten Misfit-Schichtverbindungen reduziert. Diese Reduzierung kann der turbostratischen Unordnung der Ferekristalle zugeordnet werden. Das Verhältnis zwischen der schichtsenkrechten Ginzburg-Landau-Kohärenzlänge und dem Abstand zwischen den supraleitenden Schichten ist bei den Ferekristallen kleiner als bei den nicht ungeordneten Misfit-Schichtverbindungen, was Ferekristalle zu vielversprechenden Kandidaten für (quasi-)zweidimensionale Supraleiter macht.
The investigated ferecrystals are novel layered intergrowth compounds consisting of m monolayers of niobium diselenide (NbSe2) stacked repeatedly with n atomic bilayers of lead selenide (PbSe) or tin selenide (SnSe). Bulk NbSe2 is a layered compound showing superconductivity. Due to their artificially atomic-scale layered structure, which is tunable on the atomic scale, ferecrystals can serve as model systems for layered superconductors. In this study, their structural and electrical properties are investigated. Using transmission electron microscopy their turbostratically disordered, nanocrystalline structure is revealed. The atomic structure within the individual layers is similar as for bulk NbSe2, PbSe and SnSe, with the crystallographic c-axes parallel to the stacking direction in the ferecrystals. A quantitative analysis using a two-layer model fit for the electrical resistivity, Hall coefficient and magnetoresistance yields a similar carrier type, density and mobility in the NbSe2 layers as reported for isolated NbSe2 monolayers. These values differ from those of bulk NbSe2. For the first time, a normal-to-superconducting transition has been detected in ferecrystals. The transition temperatures of the ferecrystals are reduced to about a half of those of analogous non-disordered misfit layer compounds. This reduction in transition temperature can be correlated to the turbostratic disorder in ferecrystals. The ratio between the cross-plane Ginzburg-Landau coherence length and the cross-plane distance between the NbSe2 layers for the ferecrystals is lower than for non-disordered misfit layer compounds, making ferecrystals promising candidates for (quasi-)two-dimensional superconductors.

High performance miniaturized passives are of great importance for advanced nanoelectronic packages for several applications including efficient power delivery. Low cost thin film capacitors fabricated directly on package (and/or on-chip) are an attractive approach towards realizing such devices. This thesis aims to explore fundamental frequency dependent dielectric and insulating properties of thin film high-k dielectric constant in the perovskite and perovskite-related complex oxides. Throughout this thesis, we have successfully observed the role of structure, strain and oxygen stoichiometry on the dielectric properties of thin film complex oxides, allowing a greater understanding of processing conditions and polarization mechanisms. In the first section of the thesis, we explore novel processing methods in the conventional ferroelectric, barium strontium titanate, \(Ba_{1-x}Sr_xTiO_3 (BST)\), using ultraviolet enhanced oxidation techniques in order to achieve improvements in the dielectric properties. Using this method, we also explore the growth of BST on inexpensive non-noble metals such as Ni which presents technical challenges due to the ability to oxidize at high temperatures. We observe a significant lowering of the dielectric loss while also lowering the process temperature which allows us to maintain an intimate interface between the dielectric layer and the metal electrode. The second section of this thesis explores the novel dielectric material, Lanthanum Strontium Nickelate, \(La_{2-x}Sr_xNiO_4 (LSNO)\), which exhibits a colossal dielectric response. For the first time, we report on the colossal dielectric properties of polycrystalline and epitaxial thin film LSNO. We observe a significant polarization dependence on the microstructure due to the grain/grain boundary interaction with charged carriers. We next grew epitaxial films on various insulating oxide substrates in order to decouple the grain boundary interaction. Here we observed substrate dependent dielectric properties associated with induced strain. We also observe, due to the p-type carriers in LSNO, pn junction formation when grown epitaxially on the conducting oxide degenerate n-type Nb-doped \(SrTiO_3\). Finally we explore the growth mechanism of epitaxial LSNO as a function of high oxygen content. Due to the ability for LSNO to take in interstitial oxygen, a reoriented growth is observed at a critical thickness, thereby allowing us to vary anisotropy as a function of deposition conditions.
Engineering and Applied Sciences