A comparison of different Fourier transform procedures for analysis of diffraction data from noble gas fluids

A comparison is made between the three principal methods for the analysis of neutron and x-ray diffraction data from noble gas fluids by direct Fourier transform. All three methods (standard Fourier transform, Lorch modification, and Soper–Barney modification) are used to analyze four different sets of diffraction data from noble gas fluids. The results are compared to the findings of a full-scale real-space structure determination, namely, Empirical Potential Structure Refinement. Conclusions are drawn on the relative merits of the three Fourier transform methods, what information can be reliably obtained using each method, and which method is most suitable for the analysis of different kinds of diffraction data. The mathematical validity of the Lorch method is critically analyzed

Magnesium based materials for hydrogen based energy storage: Past, present and future

Magnesium hydride owns the largest share of publications on solid materials for hydrogen storage. The “Magnesium group” of international experts contributing to IEA Task 32 “Hydrogen Based Energy Storage” recently published two review papers presenting the activities of the group focused on magnesium hydride based materials and on Mg based compounds for hydrogen and energy storage. This review article not only overviews the latest activities on both fundamental aspects of Mg-based hydrides and their applications, but also presents a historic overview on the topic and outlines projected future developments. Particular attention is paid to the theoretical and experimental studies of Mg-H system at extreme pressures, kinetics and thermodynamics of the systems based on MgH2, nanostructuring, new Mg-based compounds and novel composites, and catalysis in the Mg based H storage systems. Finally, thermal energy storage and upscaled H storage systems accommodating MgH2 are presented

High-Pressure Synthesis of Novel Polyhydrides of Zr and Hf with a Th₄H₁₅-Type Structure

The reaction of ZrH2 and HfH2 with molecular hydrogen was studied by in situ X-ray diffraction in a diamond anvil cell at room temperature at high pressures of up to 39 GPa. The formation of novel zirconium and hafnium hydrides was observed at 8.2(5) and 12.4(5) GPa, respectively. These new hydrides had the cI16-type structure of a metal lattice, identical to that of Th4H15, and the compositions of new hydrides were estimated to be Zr4H15 and Hf4H15 on the basis of their lattice volumes. The decomposition of these hydrides back into ZrH2 and HfH2 during decompression was observed at 3.5(3) and 3(1) GPa, respectively. Electrical resistance measurements indicated that Hf4H15 is a superconductor with Tc ≈ 4.5 K at 23 GPa

Pressure-induced metallization in Erbium trihydride

Electrical resistivity and Raman spectra of ErH3 were studied in a diamond anvil cell under high pressure up to 140 GPa in the temperature range 4–300 K. A crossover from a semiconductor-like to a metallic temperature dependence of resistivity at fixed pressures was observed at about 50 GPa. In the pressure range 80–140 GPa a resistivity maximum was observed at the R(T) dependencies. The temperature corresponding to this maximum linearly increased with pressure increase, reaching 26 K at 140 GPa. No superconductivity was observed in the studied pressure-temperature range

Synthesis of osmium hydride under high hydrogen pressure

The osmium-hydrogen system was studied at pressures up to 186 GPa by in situ synchrotron x-ray diffraction in a diamond anvil cell. Hydrogen solubility in the hexagonal close-packed (hcp) osmium metal at room temperature was found to be negligibly small in the studied pressure range. After laser heating of the osmium sample at the maximal H2 pressure, it transformed to hydride with a face-centered cubic (fcc) metal lattice. The equation of state V(P) for this hydride was then measured at room temperature and decreasing pressure. The hydrogen-induced volume expansion of the Os lattice proved to be weakly dependent on the pressure, and its estimated value of 1.35Å3/Os atom at 100 GPa suggested the formation of monohydride OsH with hydrogen atoms occupying all octahedral interstices in its fcc metal lattice. The OsH sample began to gradually lose hydrogen at pressures below about 55 GPa and completely decomposed to hcp-Os and molecular H2 at about 25 GPa

Superconductivity at 215 K in lanthanum hydride at high pressures

We synthesized lanthanum hydride (LaHx) by laser heating of lanthanum in hydrogen atmosphere at pressure P = 170 GPa. The sample shows a superconducting step at 209 K and 170 GPa and temperature dependence of resistance. By releasing the pressure to 150 GPa, the superconducting transition temperature Tc increases to 215 K - the record Tc. This finding supports a way of achieving Tc higher than the one in H3S (203 K) in hydrides with sodalite-like structures, first proposed for CaH6 (Tc=245 K) and later for yttrium and lanthanum hydrides where higher, room temperature superconductivity is expected