Revisiting phase stability and superconductivity in Ca-H superhydrides with anharmonic effects

Abstract

The prediction of superconductivity above 200 K in CaH6 revolutionized research on hydrogen-rich superconductors, and subsequent experiments have verified this prediction, while unidentified peaks in x-ray diffraction and the decrease in superconducting temperature upon decompression indicate that unresolved issues remain. In this work, we reconstructed the accurate temperature-pressure phase diagram of the Ca-H system and determined the stability ranges of its candidate superconducting phases by considering anharmonic effects. Our results demonstrate that type-I clathrate Ca8H46−δ structures become thermodynamically stable at 0 K when anharmonic effects are considered. Notably, we found that the previously predicted CaH6 phase achieves stability above 500 K, underscoring the significant role of temperature and anharmonic effects in stabilizing this high-pressure phase. Our findings offer insights into the structure and superconducting mechanisms of hydrides.

Source-reported materials — not catalogue approval

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