The main focus of this thesis is to study solid-state reaction pathways by controlling structures during the synthesis of scandium vanadium oxides. Besides the synthesis of structures involving different oxidation states, the stable phases were identified by means of ex-situ powder X-ray diffraction as well as in-situ high temperature oxidation. For the synthesis of Sc4/3V2/3O3 (Sc2VO4.5) and Sc2VO5 optimized methods are presented for the formation of a cubic bixbyite-type and tetragonal phase, respectively. In an ex-situ study Sc2VO5 was obtained by oxidation of Sc4/3V2/3O3 (Sc2VO4.5). A deeper understanding of the structural changes can be obtained by focussing on the sub-lattices throughout the reaction pathway. The phase change from cation-disordered bixbyite Sc2VO4.5 to cation-ordered tetragonal Sc2VO5 was studied through oxidation in trace amounts of oxygen. Moreover, the oxidation of bi-phasic samples of Sc4/3V2/3O3 (Sc2VO4.5) and Sc2VO5 clearly indicates the competition of thermodynamic and kinetic routes during heating. Thermodynamic and kinetic oxidation products were compared based on the high temperature in-situ oxidation as well as ex-situ experiments. The product of topotactic oxidation of bixbyite Sc4/3V2/3O3 (Sc2VO4.5) crystallizes in a defect fluorite structure Sc4/3V2/3O3+ε, (= Sc2VO5+δ). The oxidation of the Sc4/3V2/3O3 (Sc2VO4.5) bixbyite phase results in the formation of the reconstructed tetragonal Sc2VO5 structure at high. This finding is contrasted with the low temperature topotactic oxidation resulting in a disordered defect fluorite phase. Moreover, the conventional solid state method was used to explore the possibility of obtaining tetragonal Sc2VO5. The results showed that solid state methods might not be suitable for the preparation of Sc2VO5. / February 2017

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 T_N. 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<sub<0.5</sub>O which adopt the rock salt structure with a disordered arrangement of the cations. The (x < 1) reduced phases are the first reported examples of extended oxides which contain manganese centres with an average oxidation state of below 2. Variable temperature neutron diffraction data reveal that the La₁_-ₓCaₓMnO₃_-y (x= 0.6, 0.67 and 0.7) reduced phases adopt G-type antiferromagnetically ordered magnetic structures below approximately T_N ~ 220 K. The structure of Sr₃Fe₂O₅Cl₂ is closely related to that of the A₃B₂O₇ n = 2 Ruddlesden-Popper structure. The topotactic reduction reaction of Sr₃Fe₂O₅Cl₂ with LiH results in the formation of the Fe(II) phase Sr₃Fe₂O₄Cl₂. Neutron powder diffraction data show that Sr₃Fe₂O₄Cl₂ adopts a body-centred tetragonal crystal structure with anion vacancies located within the central SrO layer of the phase. The structure of Sr₃Fe₂O₄Cl₂ is therefore a rare example of a structure consisting of infinite sheets of corner-sharing Fe(II)O₄ square planes. In addition, the effect of cobalt-doping on the magnetic properties of the isostructural Sr₃Fe₂_-ₓCoₓO₄Cl₂ (0 ≤ x ≤ 1) series of reduced phases was investigated. Cobalt-doping was found to frustrate the antiferromagnetic order initially leading to a decrease in the magnetic ordering temperature but ultimately leading to spin glass behaviour.

Topochemical strategies, techniques that allow one to effectively manipulate the structures of nonmolecular solids once a crystal lattice is established, are effective in the low temperature (< 500 °C) modification of solid state structures, allowing the preparation of nonmolecular compounds not accessible by standard synthetic routes. Some of the techniques, ion exchange, intercalation/deintercalation, have proven to be excellent synthetic methods for preserving specific frameworks. The combination of these techniques can allow one to create a multistep approach that can be used to design new compounds with interesting properties. As an expansion to the field of topotactic reactions, a multistep approach was developed towards the synthesis of the new compounds (A xM0.5Cly)LaNb2O7 (where A = Rb, Cs; M = Fe, Ni; x ≈ 1.5;y ≈ 1) at temperatures below 400oC. The first reaction step involved the ion exchange of the host materials (ALaNb2O7, A = Rb, Cs) to form the products M0.5LaNb2O7 (where M = Fe, Ni), a structure open to further chemistry. The next step involved reductive intercalation with Rb or Cs metal to form the air sensitive mixed-valence products with the nominal compositions, A1.5M0.5LaNb2O7. The last step involved the oxidative intercalation of chlorine using chlorine gas to obtain the final compounds. This multistep approach is a design to form mix-metal halide layers, specifically those with divalent cations, within layered perovskites, opening the doors to compounds that can have interesting properties. This reaction series was also applied to the tantalate layered oxides, leading to the formation of the new compound Ni 0.5LaTa2O7 through ion exchange. The further multistep topochemical manipulation of this new compound was not successful and was indicative of the difference in chemical behavior of the tantalates versus the niobates. We have also investigated the oxidative intercalation of halogens into a series of Ruddlesden-Popper (R-P) ruthenate oxides with the formula Ae n+1RunO3n+1 (Ae = Ca, Sr; n = 1, 2, 3) using several sources of fluorine, chlorine, and bromine. A new method was developed to intercalate chlorine into layered systems; this new approach avoids the use of chlorine gas which is highly toxic. The new phase Sr3Ru2O7Cl0.7 was synthesized by the new method and further topotactic manipulations were explored. The chemistry was not limited to the n = 2 phase but was also applied to the n = 3 phase, Sr4Ru3O10.

Over the last decade progress towards step-wise structural transformations in solid state chemistry has been made using metal hydride reductants. Alkali and alkali-earth metal hydrides can effectively reduce transition metal oxides resulting frequently in novel oxygen defect structures. This provides access to control over cation oxidation states and magnetic exchange pathways, and thus electronic and magnetic properties. The goal for this research was to investigate a representative system that could be used both for exploration of novel oxygen defect phases and for investigating the fundamental parameters governing successful solid state reductions. The systems chosen for investigation were Sr2-xCaxMnO4 (0<x<2) and Sr2-xBaxMnO4 (x< 0.04). Detailed analysis of metal hydride reactivity with Sr2MnO4 is presented in addition to proof of the solid state reduction mechanism. As a result a number of novel oxygen defect phases have been produced, Sr2MnO4-x (0<x<0.37). The potential for producing novel lithium doped Sr2MnO4-x phases using a reduction/insertion approach with LiH has also been identified. Lastly as a test of application for metal hydrides as reductants the ability to topotactically reduce ScVO4 has been investigated.

Over the last decade progress towards step-wise structural transformations in solid state chemistry has been made using metal hydride reductants. Alkali and alkali-earth metal hydrides can effectively reduce transition metal oxides resulting frequently in novel oxygen defect structures. This provides access to control over cation oxidation states and magnetic exchange pathways, and thus electronic and magnetic properties. The goal for this research was to investigate a representative system that could be used both for exploration of novel oxygen defect phases and for investigating the fundamental parameters governing successful solid state reductions. The systems chosen for investigation were Sr2-xCaxMnO4 (0<x<2) and Sr2-xBaxMnO4 (x< 0.04). Detailed analysis of metal hydride reactivity with Sr2MnO4 is presented in addition to proof of the solid state reduction mechanism. As a result a number of novel oxygen defect phases have been produced, Sr2MnO4-x (0<x<0.37). The potential for producing novel lithium doped Sr2MnO4-x phases using a reduction/insertion approach with LiH has also been identified. Lastly as a test of application for metal hydrides as reductants the ability to topotactically reduce ScVO4 has been investigated.

The full crystal structures of three polymorphs of 4-methyl-2-nitroacetanilide (MNA) are described. The white form (MNA-l), is the most stable form. The least stable form is the amber farm (MNA-2). The yellow form (MNA-3) has been found to change in a topotactic manner into the white form. The relationships between the three polymorphs are discussed and possible mechanisms to account for the topotactic phase changes are presented. The polymorphs show different i.r. and Raman spectra in the solid state. These spectra, and those of deuterated analogues are interpreted and their differences explained. A study of the proton and 13-C n.m.r. spectra show that the conformation of flexible MNA molecules is markedly dependent on the nature of the solvent. The ability of other o-nitroacetanilides to exist in a white (intermolecular) and yellow (intramolecular hydrogen bonded) forms has been examined. Finally, details of the synthesis of these compounds and an account of the examination of MNA polymorphs by differential scanning calorimetry (d.s.c) are described. A description of computer programs used, including one in BASIC which will enable the contents of unit cell(s) to be viewed, is given.

Orientador: Heloise de Oliveira Pastore / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-21T15:14:46Z (GMT). No. of bitstreams: 1 Ramos_FranciscaSolaneadeOliveira_M.pdf: 5550553 bytes, checksum: c97e45758df14cd712ea691a6174a574 (MD5) Previous issue date: 2012 / Resumo: A aplicação dos silicatos lamelares como catalisadores apresenta como limitações as baixas área superficial e acidez, porém, esses sólidos têm como principais propriedades a reatividade dos grupos Si-OH e Si-ONa da superfície de suas lamelas e sua capacidade de troca iônica. Em função disso, esses sólidos podem sofrer uma variedade de modificações em sua superfície e em seu espaço lamelar e até passar de uma estrutura 2D para uma estrutura 3D. As lamelas do silicato lamelar Na-RUB-18, além de serem recobertas por Si-OH e Si-O, são constituídas de cavidades de quatro anéis de cinco membros [5], presentes tanto no RUB-24 quanto na MOR, assim como em outros zeólitos, indicando que tal lamelar seja potencial precursor de estruturas zeolíticas. Por tais motivos, o presente trabalho teve como objetivo estudar e descrever como o Na-RUB-18 se transforma nas estruturas zeolíticas MOR e RUB-24, por processos hidrotérmico e topotático, respectivamente, e como essas estruturas 2D e 3D se relacionam. A gradual aproximação das lamelas do Na-RUB-18 e conseqüente condensação dos grupos Si-OH, ou seja, unidades Q ([O4Si]3Si-OH), ocasiona a formação de ligações Si-O-Si, unidades Q ([O4Si]4-Si), gerando a estrutura 3D. No caso do zeólito MOR, esse processo é induzido pela adição de uma fonte de alumínio, Al[OCH(CH3)2]3 ou Na2Al2O4. O presente trabalho também investiga a etapa de aproximação das lamelas do Na-RUB-18, ocasionando na sua condensação em RUB-24. A condensação das lamelas do precursor lamelar no RUB-24 via processo topotático é conduzida por um agente direcionador de estrutura, o íon trietilenotetramônio, comprovando que tal processo, como a transformação hidrotérmica, não acontece aleatoriamente / Abstract: The application of the layered silicates in heterogeneous catalysis has limitations such as low surface area and acidity. However, these solids also have ion exchange capacity and their surfaces can be covalently modified with silylation reagents. As a result, they can undergo a variety of surface changes yielding modifications in interlayer space and in the structure lamellar that may even cause collapse of a 2D structure to a 3D. The framework of layered silicate Na-RUB-18 is composed of four five-membered rings, [5] and its surface made of Si-OH and Si-ONa. The [5] cage is a building unit also found in zeolitic structures, as RUB-24 and MOR, indicating that the structure of Na-RUB-18 contains important elements of microporous materials structures and should be regarded as a potential precursor structure to the three-dimensional four-connected microporous framework silicates. This work aimed of studying and describing the transformations of the Na-RUB-18 into MOR and RUB-24 by hydrothermal and topotactic process, respectively. The gradual reduction of interlayer distance of the Na-RUB-18 led to the condensation of the Si-OH groups, Q units ([O4Si]3Si-OH), forming Si-O-Si bonds, Q units ([O4Si]4-Si), i.e., a 3D structure. In the preparation of MOR zeolite by hydrothermal transformation, the process is conducted through addition of a aluminum source, Al[OCH(CH3)2]3 or Na2Al2O4. This work also investigated the formation of RUB-24 through Na-RUB-18 collapsing. The topotactic reaction between Si-OH groups of the lamellar precursor was conducted by a structure-directing agent, triethylenetetrammonium ion, proving that this process, as the hydrothermal transformation, does not occur randomly / Mestrado / Quimica Inorganica / Mestra em Química

Double layer capacitors owe their large capacitance to high specific surface area carbon-based electrode materials adhered to a current collector via an adhesive. However, recent studies attribute greater electrical energy storage capacity to transition metal oxides/nitrides: a new generation of electrode materials for use in super-capacitors with mixed double-layer and pseudo-capacitive properties. Solution precursor plasma spray deposition is a technique that allows coatings to be fabricated with fine grain sizes, high porosity levels, and high surface area; characteristics ideal for application as super-capacitor electrodes. This investigation established conditions for deposition of porous, high specific surface area α-MoO3. It further identified a two-step temperature-programmed reaction for topotactic phase transformation of the α-MoO3 deposits into high specific surface area molybdenum nitrides of higher conductivity and higher electrochemical stability window. The electrochemical behavior of molybdenum oxide/nitride deposits was also studied in order to assess their potential for use in super-capacitors.

Double layer capacitors owe their large capacitance to high specific surface area carbon-based electrode materials adhered to a current collector via an adhesive. However, recent studies attribute greater electrical energy storage capacity to transition metal oxides/nitrides: a new generation of electrode materials for use in super-capacitors with mixed double-layer and pseudo-capacitive properties. Solution precursor plasma spray deposition is a technique that allows coatings to be fabricated with fine grain sizes, high porosity levels, and high surface area; characteristics ideal for application as super-capacitor electrodes. This investigation established conditions for deposition of porous, high specific surface area α-MoO3. It further identified a two-step temperature-programmed reaction for topotactic phase transformation of the α-MoO3 deposits into high specific surface area molybdenum nitrides of higher conductivity and higher electrochemical stability window. The electrochemical behavior of molybdenum oxide/nitride deposits was also studied in order to assess their potential for use in super-capacitors.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21122号 / 工博第4486号 / 新制||工||1697(附属図書館) / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 田中 庸裕, 教授 陰山 洋, 教授 佐藤 啓文 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM