Crystal Structure and Electrical Property of Calcium under Very High Pressure

An angular dispersive X-ray diffraction experiment on calcium metal (Ca) has been performed at high pressures up to 158 GPa. Ca forms an fcc lattice at ambient conditions and transforms to a bcc lattice at 20 GPa and to a simple cubic lattice (sc) at 32 GPa to the phase of Ca-IV. We confirmed another high-pressure phase (Ca-V) following to Ca-IV above at about 143 GPa. The electrical resistance at room temperature as well as the superconducting transition temperature T c was found to increase in the sc structure with increasing pressure and moderately increase in Ca-IV and Ca-V.