Stability and electronic structure of magnesium hydride and magnesium deuteride under high pressure

Metal polyhydrides have attracted considerable attention because some of them become a metal under high pressure, and some undergo a phase transition into a superconductor. Some superconducting metal polyhydrides have recently been discovered with a high value of critical temperature (Tc) under pressure. In this research, we calculated the structures of MgH2, MgH3 and MgD3 under pressure between 0-300 GPa in order to determine the formation enthalpy and electronic property of their structures under high pressure by using density functional theory (DFT) based on the Quantum Espresso code. We found that the band structures reveal the metallic character of the compounds under high pressure. The energy band structures of MgHx and MgDx are exactly the same. However, their phonon dispersions are different due to the so-called isotope effect. We determined the composition stability by using the convex hull of Mg, H and the compounds. We found that MgH3 becomes thermodynamically more stable than MgH2 at around 150 GPa. The results of phonons confirm that they are dynamically stable. This finding is served as a basis for future superconducting calculations.

Сверхтонкие взаимодействия в узлах меди диэлектрических и сверхпроводящих металлооксидов меди

The method of Mössbauer spectroscopy on isotopes 61Cu (61Ni) shows that for bivalent copper dielectric metal oxides, a combined quadrupole and Zeeman interaction of 61Ni nuclei with local fields in copper sites is observed, whereas for superconducting metal oxides, only quadrupole interaction of the nuclei 61Ni is detected. For all the metal oxides under consideration, the equal in value valence contribution to the electric field gradient tensor was found.

Сверхтонкие взаимодействия в узлах меди антиферромагнитных соединений, аналогов сверхпроводящих металлооксидов меди

Emission Mössbauer spectra of 61Cu(61Ni) in dielectric metal oxides of divalent copper Ca1−xSrxCuO2, Ca2CuO2Cl2, Sr2CuO2Cl2, YBa2Cu3O7−x, La2−xSrxCuO4 and Nd2−xCexCuO4 correspond to the combined quadrupole and Zeeman interaction of 61Ni nuclei with local fields at the sites of copper. For the superconducting metal oxides, on the other hand, spectra correspond to the interaction of the quadrupole moment of 61Ni nuclei with the electric field gradient. The both groups of metal oxides show linear dependences of the quadrupole interaction constants on the calculated values of the principal components of the lattice electric field gradient tensor at the copper sites for 61Ni nuclei (emission 61Cu(61Ni) Mössbauer spectroscopy data) as well as for 63Cu nuclei (63Cu nuclear magnetic resonance data). This fact is explained by invariable values of the valence component of electric field gradient for both 61Ni2+ and 63Cu2+ probes in all divalent copper metal oxides under investigation.