Raman evidence of a new high-pressure phase in calcium hydride

A new high-pressure phase of solid calcium hydride at room temperature was discovered by in situ Raman scattering experiments with a diamond anvil cell. The phase transition was found to start at similar to 15.5 GPa and complete at similar to 21 GPa, and it is reversible with a hysteresis to similar to 12 GPa, when the pressure was released. Moreover, the high-pressure phase was found to be stable up to at least 42 GPa. First-principles calculations were performed to assign the measured Raman modes at zero pressure accurately and to understand the pressure dependence of the Raman frequency shift before the transition.