Determine the superconducting phase with Tc above 210 K in Ca-H system at around 200 GPa and low temperature conditions

For calcium hydrides, CaHn (n=2, 4, 6…) were predicted to have stable structures at high pressure and show superconductivity. We just discovered experimentally the superconductivity with critical temperature Tc~ 210 K in Ca-H system. The materials are synthesized at the conditions of 160~210 GPa and ~1800 K in DAC combining with in-situ laser heating technique. The superconductivity was studied through the in-situ high pressure resistance measurements. We performed high pressure XRD experiment at room temperature and tentatively assigned the superconducting phase as CaH6 [Nature Communications, 13, 2863, 2022]. However, the superconducting state of this hydride is at around 200 K, instead of room temperature, the previous XRD experiments was not performed at correct P-T conditions yet. Therefore, we plan to carry out corresponding low temperature XRD experiment at around 160~200 GPa conditions to solve this puzzle.