The prediction of superconductivity above 200 K in ${\mathrm{CaH}}_6$ 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 ${\mathrm{Ca}}_8{\mathrm{H}}_{46-\delta }$ structures become thermodynamically stable at 0 K when anharmonic effects are considered. Notably, we found that the previously predicted ${\mathrm{CaH}}_6$ 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.

Close

PrevNext

View figure in article

• Anharmonic lattice dynamics
• High-pressure studies
• Superconductivity
• Clathrates
• Hydrides
• Superconductors
• Density functional calculations