Investigation of stable germane structures under high-pressure

Abstract

The evolutionary structure-searching method discovers that the energetically preferred compounds of germane can be synthesized at a pressure of 190 GPa. New structures with the space groups Ama2 and C2/c proposed here contain semimolecular H2 and V-type H3 units, respectively. Electronic structure analysis shows the metallic character and charge transfer from Ge to H. The conductivity of the two structures originates from the electrons around the hydrogen atoms. Further electron-phonon coupling calculations predict that the two phases are superconductors with a high Tc of 47-57 K for Ama2 at 250 GPa and 70-84 K for C2/c at 500 GPa from quasi-harmonic approximation calculations, which may be higher than under actual conditions.

Superconductivity and unexpected chemistry of germanium hydrides under pressure

“…At 250 GPa, the tetragonal Ge 3 H 11 with space group I4m2 is still metastable and lies just above the tie-line joining Ama2-GeH 4 and Pnma-Ge 2 H. At 300 GPa, we predict stable phases: Ge 3 H (P6 3 /m), Ge 2 H (Pnma) and GeH 3 (Cccm) in accord with previous predictions 9,20 . In addition, we also found unexpected composition Ge 3 H 11 that appears in the H-rich region, its structure featuring GeH 12 distorted icosahedra and GeH 16 Frank-Casper polyhedra.…”

“…1. To our surprise, in addition to reproducing various structures of Ge-H system 4,9,20,36 , Ge 37 and H 2 38 , previously unreported and unexpected composition of germanium hydrides Ge 3 H 11 was found to be stable in wide pressure ranges.…”

“…In addition, we also found unexpected composition Ge 3 H 11 that appears in the H-rich region, its structure featuring GeH 12 distorted icosahedra and GeH 16 Frank-Casper polyhedra. Moreover, germane transforms to a new monoclinic phase with space group C2/m with 3 f.u./cell at above 300 GPa (278 GPa with inclusion of ZPE), which is lower in enthalpy than all previously proposed structures 4,9,20 (see also Fig. 2(b)).…”

“…C2/c was predicted to be a superconductor with T c = 64 K at 220 GPa. In a recent theoretical study, a more energetically stable structure of germane (with symmetry group Ama2) was predicted by Zhang et al to have T c of 47-57 K 20 . Now, with major progress of computational methods (enabling, for example, variable-composition searches), we can address all the outstanding issues.…”

The Search for Superconductivity in High Pressure Hydrides

“…292 Recently, CSP techniques have predicted two hitherto unknown GeH 4 phases, one with Ama2 symmetry at 250 GPa and one with C2/c symmetry at 500 GPa, to be thermodynamically, mechanically and dynamically stable with estimated T c values of 47-57 and 70-84 K, respectively. 293 Spectroscopic evidence has shown that germane and H 2 can form a compound with the approximate GeH 4 (H 2 ) 2 stoichiometry at pressures of 7.5-27 GPa. 297 The GeH 4 molecules within this phase are rotationally disordered and occupy fcc sites, whereas the H 2 molecules fill both octahedral and tetrahedral lattice sites.…”