# Superconductivity and unexpected chemistry of germanium hydrides under pressure

## TL;DR

This study predicts new stable germanium hydrides under high pressure, revealing their structures, stability, and superconducting properties, and highlights their unique phase behavior compared to similar elements.

## Contribution

It introduces a new stable germanium hydride structure with superconductivity, expanding understanding of high-pressure hydrides and their phase stability.

## Key findings

- New C2/m germanium hydride stable above 278 GPa
- Superconductivity with T$_c$ = 67 K at 280 GPa
- Decomposition to Ge$_3$H$_{11}$ with T$_c$ = 43 K above 285 GPa

## Abstract

Following the idea that hydrogen-rich compounds might be high-T$_c$ superconductors at high pressures, and the very recent breakthrough in predicting and synthesizing hydrogen sulfide with record-high T$_c$ = 203 K, ab initio evolutionary algorithm for crystal structure prediction was employed to find stable germanium hydrides. In addition to the earlier structure of germane with space group Ama2, we propose a new C2/m structure, which is energetically more favorable at pressures above 278 GPa (with inclusion of zero point energy). Our calculations indicate metallicity of the new C2/m phase of germane with T$_c$ = 67 K at 280 GPa. Germane is found to exhibit thermodynamic instability to decomposition to hydrogen and the new compound Ge$_3$H$_{11}$ at pressures above 300 GPa. Ge$_3$H$_{11}$ with space group I$\bar{4}$m2 is found to become stable at above 285 GPa with T$_c$ = 43 K. We find that the pressure-induced phase stability of germanium hydrides is distinct from its analogous isoelectronic systems, e.g., Si-hydrides and Sn-hydrides. Superconductivity stems from large electron-phonon coupling associated with the wagging, bending and stretching intermediate-frequency modes derived mainly from hydrogen.