Magnesium based alloys are promising solid materials for hydrogen storage. However, it is a real challenge to synthesise hydrogen storage materials with high hydrogen storage capacity and low dehydrogenation temperature. Here, we have performed extensively structural searches for ternary magnesium-based hydrogen storage compounds of Mg7NbHn with n ranging from 16 to 25 by CA-LYPSO method and first-principles calculations. We readily identified the experimentally observed Mg7NbH16 hydride and uncovered a new stable stoichiometry of Mg7NbH19 with high hydrogen storage capacity of 6.7 wt-% and low dehydrogenation temperature of 273 K. The remarkable decrease of the hydrogen release temperature is attributed to the atomic rearrangements in Mg7NbH19 which forms H-H pairs and has weakened metal-hydrogen chemical bonds compared to the stable Mg7NbH16 and MgH2 compounds. Our calculations show that Mg7NbH16 undergoes a structural phase transition from its P 42m phase to a F m 3m phase at 75 GPa, and the F m 3m phase is a potential polyhydride superconductor. The present findings offer insights for understanding the hydrogen storage and release of Mg-Nb-H ternary magnesium-based hydrogen storage compounds, which open avenues for the design and synthesis of novel magnesium-based hydrogen storage material.

A systematic investigation of ternary hydride MgVH6 within the pressure range of 0–200 GPa has been performed by means of the particle swarm optimization algorithm and density functional theory. Results of an extensive structure search and full relaxation further indicate that three new phases, P21/m, C2/m, and Pmn21, appear successively with the increasing of pressure, which contain two first-order structural phase transitions from P21/m to C2/m about 32 GPa and from C2/m to Pmn21 about 93 GPa. Three phases are all metallic phases by analyzing their band structures and density of electronic states and are also dynamically and mechanically stable based on their phonon spectra and elastic properties. More importantly, the electron–phonon coupling calculation indicates that MgVH6 with Pmn21 symmetry is a promising superconductor with an estimated superconducting transition temperature of 27.6 K at 150 GPa, which is similar to the superconducting transition temperature of 35 K at 300 GPa of ternary hydride LaSH6 (Phys. Rev. B 2019, 100, 184502). Further analysis of the electron–phonon coupling mechanism shows that the superconductivity is mainly derived from the strong electron–phonon interaction of heavier transition metal V atoms.

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The structural phase transition, ferroelectric polarization, and electric properties have been investigated for photovoltaic films CsMI3 (M = Pb, Sn) epitaxially grown along (001) direction based on the density functional theory.

We perform the first-principles calculations combined with the particle swarm optimization algorithm to investigate the high-pressure phase diagrams of NaF3 (  =  Mn, Ni, Zn). Two reconstructive phase transitions are predicted from Pv- to pPv- at about 9 GPa and pPv- to ppPv- at around 26 GPa for NaZnF3. That is not the case for NaMnF3—a direct transition (reconstructive transition in nature but with the same Pnma space group) from Pv- to ppPv- phase around 12 GPa. Strikingly, our simulated results manifest that a disproportionation phase of NaZnF3 post-perovskite is uncovered along the way, which provides a successful explanation for the observed results in experiment. Additionally, the mechanical and thermal properties, especially the dynamical property, of the four NaZnF3 phases have also been studied. Here, we reveal the obvious softening of -wave velocity and bulk sound speed in pPv-–to–ppPv- transition, which may result in the discontinuity of seismic waves propagation through the Earth’s interior.

We mainly probe into phase stabilities, structural characters, elastic anisotropy and bonding features of the iridium borides under ambient pressure.

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