Alkali (A) and alkaline earth (AE) metals can form carbides and intercalated graphites with carbon. The carbides mostly represent acetylides which are salt-like compounds composed of C22− dumbbell anions and metal cations. Both the acetylide carbides and intercalated graphites are technologically important. Superconductivity has been observed in several intercalated graphites such as KC8 and CaC6. Li intercalated graphites are a major ingredient in Li ion batteries. CaC2 is an important commodity for producing acetylene and the fertilizer CaCN2. In spite of the extensive research on A–C and AE–C compounds, phase diagrams are largely unknown. The thermodynamic and kinetic properties of both carbides and intercalalated graphites are discussed controversially. Recent computational studies indicated that well-known carbides, like CaC2 and BaC2, are thermodynamically unstable. Additionally, computational studies predicted that acetylide carbides will generally form novel polymeric carbides (polycarbides) at high pressures. This thesis is intended to check the validity of theoretical predictions and to shed light on the complicated phase diagrams of the Li–C and the Ca–C systems. The Li–C and the Ca–C systems were investigated using well-controllable metal hydride–graphite reactions. Concerning the Li–C system, relative stabilities of the metastable lithium graphite intercalation compounds (Li-GICs) of stages I, IIa, IIb, III, IV and Id were studied close to the competing formation of the thermodynamically stable Li2C2. The stage IIa showed distinguished thermal stability. The phase Id showed thermodynamic stability and hence, was included in the Li–C phase diagram. In the Ca–C system, results from CaH2–graphite reactions indicate compositional variations between polymorphs I, II and III. The formation of CaC2  I was favored  only  at  1100  ◦C or  higher  temperature  and  with  excess calcium, which speculates phase I as carbon deficient CaC2−δ . To explore the potential existence of polycarbides, the acetylide carbides Li2C2 and CaC2 were investigated under various pressure and temperature conditions, employing diamond anvil cells for in situ studies and multi anvil techniques for large volume synthesis. The products were characterized by a combination of diffraction and spectroscopy techniques. For both Li2C2 and CaC2, a pressure induced structural transformation was observed at relatively low pressures (10–15 GPa), which was followed by an irreversible amorphization at higher pressures (25–30 GPa). For Li2C2 the structure of the high pressure phase prior to amorphization could be elucidated. The ground state with an antifluorite Immm structure (coordination number (CN) for C22− dumbbells = 8) transforms to a phase with an anticotunnite Pnma structure (CN for C22− dumbbells = 9). Polycarbides, as predicted from theory, could not be obtained. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.</p>

The synthesis of a scandium aluminium methylphosphonate ScAl₃(CH₃PO₃)₆ isostructural to the aluminium methylphosphonate AlMePO-α and with permanent microporosity is reported here for the first time. Structural characterisation of three lanthanide bisphosphonate structures (I,II,III) with the light lanthanides and N,N'-piperazine bis-(methylenephosphonic acid) and its 2-methyl and 2,5-dimethyl derivatives is described. The framework of structure type I shows considerable flexibility upon dehydration with a symmetry change from C2/c, a = 23.5864(2) Å, b = 12.1186(2) Å, c = 5.6613(2) Å, β = 93.040(2)˚) in the hydrated state to P2₁/n, a = 21.8361(12) Å, b = 9.3519(4) Å, c = 5.5629(3) Å, β = 96.560(4)˚ after dehydration. This cell volume reduces by 27% on dehydration and is accompanied by a change in the conformation of the piperazine ring from chair to boat configuration. The structures of type I (hydrated and dehydrated) were refined against synchrotron powder X-ray diffraction data. Despite the reversible hydration and flexibility, the structures possess no permanent porosity. Investigation of the solvothermal chemistry of scandium carboxylates identified routes to 7 framework structures 5 of which were previously unreported in the scandium system. Lower temperature solvothermal reactions using terephthalic acid (80 - 140°C using dimethylformamide and diethylformamide) yielded two scandium terephthalates, MIL-88B(Sc) and MIL-101(Sc), identified by laboratory X-ray powder diffraction. Whereas higher temperature (160 – 220°C), reactions gave MIL-53(Sc) and Sc₂BDC₃. Further study with the tri- and tetra-carboxylate linkers, trimesic acid, 3,3',5,5'-azobenzenetetracarboxylic acid and pyromellitic acid yielded MIL-100(Sc), Sc-ABTC and Sc₄PMA₃ respectively. Structural identification of MIL-100(Sc) and Sc-ABTC was performed by means of X-ray powder diffraction analysis and of Sc₄PMA₃ by single crystal X-ray diffraction. The structure of a small pore scandium terephthalate Sc₂BDC₃ was investigated as a function of temperature and of functionalization. In situ synchrotron X-ray diffraction data, collected on a Sc₂BDC₃ in vacuo, enabled a phase change from orthorhombic Fddd to monoclinic C2/c and the associated structural effects to be observed in detail. The orthorhombic structure displayed a negative thermal expansivity of 2.4 × 10⁻⁵ K⁻¹ over the temperature range 225 – 523 K which Rietveld analysis showed to be derived from carboxylate group rotation. Motion within the framework was studied by ²H wide-line and MAS NMR on deuterated Sc₂BDC₃ indicating π flips can occur in the phenyl rings above 298 K. The effects of functionalization on the Sc₂BDC₃ framework were investigated by reactions using the 2-amino- and 2-nitroterephthalic acid and gave evidence for a strong structural effect resulting from inclusion of the functional groups. The structure of Sc₂BDC₃ and the functionalised derivatives were solved using Rietveld analysis on synchrotron X-ray powder diffraction data. Sc₂(NH₂-BDC)₃ was solved using the orthorhombic Sc₂BDC₃ framework starting model and, over the temperature range studied, stayed orthorhombic Fddd. Sc₂(NO₂-BDC)₃, was shown to be monoclinic C2/c over the same temperature range, a result of the steric effects of the bulky –NO₂ group in a small pore framework. Partial ordering of the functional groups was observed in both Sc₂(NH₂-BDC)₃ and Sc₂(NO₂-BDC)₃. The strength of interaction for the Sc₂(NH₂-BDC)₃ with CO₂ was higher than that of the parent Sc₂BDC₃ due to the strong –NH₂•••CO₂ interaction. Despite the inclusion of a relatively large –NO₂ group along the walls of a channel ~4 Å in diameter the Sc₂(NO₂-BDC)₃ still showed permanent microporosity to CO₂ (2.6 mmol g⁻¹) suggesting that there must be some motion in the -NO₂ group to allow the CO₂ molecules to diffuse through the channels. The scandium analogue of the flexible terephthalate MIL-53, a competitive phase in the synthesis of Sc₂BDC₃, was prepared and characterised by Rietveld analysis on synchrotron X-ray powder diffraction data using a combination of literature structural models and models obtained from single crystal X-ray diffraction experiments. Experimental solid state ⁴⁵Sc, ¹³C and ¹H NMR data combined with NMR calculations on the structural models produced from diffraction analysis were used to identify the hydrated (MIL-53(Sc)-H₂O), calcined (MIL-53(Sc)-CAL) and high temperature (MIL-53(Sc)-HT) structures of MIL-53(Sc). Further to this the 2-nitroterephthalate derivative, MIL-53(Sc)-NO₂, was prepared and characterised using single crystal X-ray diffraction. The adsorptive properties of the parent terephthalate and the functionalised derivative were compared and in both cases showed a breathing behaviour, exemplified by steps in the adsorption isotherms. MIL-53(Sc)-CAL was found to possess a closed pore configuration in the dehydrated state, a previously unreported structural form for the MIL-53 series, and its presence can be observed in the low pressure region of the CO₂ adsorption isotherm as a non-porous plateau. The selectivity and separation properties of two MOFs, the nickel bisphosphonate, STA-12(Ni) and the scandium carboxylate, Sc₂BDC₃ were measured using breakthrough curves on mixtures of CH₄ and CO₂. The results showed both materials to be highly selective in the adsorption of CO₂ over CH₄. Column testing using a PLOT column of STA-12(Ni) and a packed column of Sc₂BDC₃ showed promising preliminary results with STA-12(Ni) displaying effective, baseline separation on low boiling point hydrocarbon mixtures (C1 – C4) while the smaller pore channels of Sc₂BDC₃ were effective in the size selective separation of higher boiling point branched and straight-chain hydrocarbons (C5 – C7).

The response of materials under extreme temperature and pressure conditions is a topic of great significance because of its relevance in astrophysics, geophysics, and inertial confinement fusion. In recent years, environments exceeding several hundred gigapascals in pressure have been produced in the laboratory via laser-based dynamic loading techniques. Shock-loading is of particular interest as the shock provides a fiducial for measuring time-dependent processes in the lattice such as phase transitions. Time-resolved x-ray diffraction is the only technique that offers an insight into these shock-induced processes at the relevant spatial (atomic) and temporal scales. In this study, nanosecond resolution x-ray diffraction techniques were developed and implemented towards the study of shock-induced phase transitions in polycrystalline materials. More specifically, the capability of a focusing x-ray diffraction geometry in high-resolution in situ lattice measurements was demonstrated by probing shock-compressed Cu and amorphous metallic glass samples. In addition, simultaneous lattice and free surface velocity measurements of shock-compressed Mg in the ambient hexagonal close packed (hcp) and shock-induced body centered cubic (bcc) phases between 12 and 45 GPa were performed. These measurements revealed x-ray diffraction signals consistent with a compressed bcc lattice above a shock pressure of 26.2±1.3 GPa, thus capturing for the first time direct lattice evidence of a shock-induced hcp to bcc phase transition in Mg. Our measurement of the hcp-bcc phase boundary in Mg was found to be consistent with the calculated boundary from generalized pseudopotential theory in the pressure and temperature region intersected by the principal shock Hugoniot. Furthermore, the subnanosecond timescale of the phase transition implied by the shock-loading conditions was in agreement with the kinetics of a martensitic transformation. In conclusion, we report on the progress and future work towards time-resolved x-ray diffraction measurements probing solid-liquid phase transitions in high Z polycrystalline materials, specifically Bi. / text

<p>This thesis is concerned with <i>in-situ</i> time-, temperature- and pressure-resolved synchrotron X-ray powder diffraction investigations of a variety of inorganic compounds with twodimensional layer structures and three-dimensional framework structures. In particular, phase stability, reaction kinetics, thermal expansion and compressibility at non-ambient conditions has been studied for 1) Phosphates with composition <i>M</i><i>IV</i>(HPO₄)₂·<i>n</i>H₂O (<i>M</i><i>IV</i> = Ti, Zr); 2) Pyrophosphates and pyrovanadates with composition<i> M</i><i>IV</i>X₂O₇(<i>M</i><i>IV</i> = Ti, Zr and X = P, V); 3) Molybdates with composition ZrMo₂O₈. The results are compiled in seven published papers and two manuscripts.</p><p>Reaction kinetics for the hydrothermal synthesis of α-Ti(HPO₄)₂·H₂O and intercalation of alkane diamines in α-Zr(HPO₄)₂·H₂O was studied using time-resolved experiments. In the high-temperature transformation of γ-Ti(PO₄)(H₂PO₄)·2H₂O to TiP₂O₇ three intermediate phases, γ'-Ti(PO₄)(H₂PO₄)·(2-x)H₂O, β-Ti(PO₄)(H₂PO₄) and Ti(PO₄)(H₂P₂O₇)_0.5 were found to crystallise at 323, 373 and 748 K, respectively. A new tetragonal three-dimensional phosphate phase called τ-Zr(HPO₄)₂ was prepared, and subsequently its structure was determined and refined using the Rietveld method. In the high-temperature transformation from τ-Zr(HPO₄)₂ to cubic α-ZrP₂O₇two new orthorhombic intermediate phases were found. The first intermediate phase, ρ-Zr(HPO₄)₂, forms at 598 K, and the second phase, β-ZrP₂O₇, at 688 K. Their respective structures were solved using direct methods and refined using the Rietveld method. <i>In-situ</i> high-pressure studies of τ-Zr(HPO₄)₂revealed two new phases, tetragonal ν-Zr(HPO₄)₂and orthorhombic ω-Zr(HPO₄)₂ that crystallise at 1.1 and 8.2 GPa. The structure of ν-Zr(HPO₄)₂ was solved and refined using the Rietveld method.</p><p>The high-pressure properties of the pyrophosphates ZrP₂O₇ and TiP₂O₇, and the pyrovanadate ZrV₂O₇were studied up to 40 GPa. Both pyrophosphates display smooth compression up to the highest pressures, while ZrV₂O₇ has a phase transformation at 1.38 GPa from cubic to pseudo-tetragonal β-ZrV₂O₇ and becomes X-ray amorphous at pressures above 4 GPa.</p><p>In-situ high-pressure studies of trigonal α-ZrMo₂O₈ revealed the existence of two new phases, monoclinic δ-ZrMo₂O₈and triclinic ε-ZrMo₂O₈ that crystallises at 1.1 and 2.5 GPa, respectively. The structure of δ-ZrMo₂O₈was solved by direct methods and refined using the Rietveld method.</p>

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.