New high-pressure phase of calcium

An angular dispersive X-ray diffraction experiment on calcium metal (Ca) has been performed at high pressures up to 139 GPa. Ca forms a face-centered cubic (fcc) lattice at ambient conditions, transforms to a body-centered cubic (bcc) lattice at 20GPa, and further transforms to a simple cubic structure at 32 GPa. We found the simple cubic phase in a wide pressure range, from 32 to about 109 GPa, and discovered a new high-pressure phase above 113 GPa.