Electronic phase transitions in cadmium at high pressures

Abstract

Elemental solid Cd crystallizes in the hcp structure with a large c/a value of 1.89. This leads to anisotropy in the Fermi-surface topology, electron-transport and other physical properties. Application of pressure reduces this anisotropy, with the c/a ratio decreasing to the ideal value corresponding to a spherical Fermi surface. There is long standing interest in the detection of departures of c/a from a smooth variation with pressure, and in associating such anomalies with electronic topological transitions. Angular x-ray diffraction measurements were carried out on Cd up to 25 GPa at room temperature. Variations of c/a with pressure reveal anomalies near 2, 7, 15 and 22 GPa; we find anomalies in the pressure-volume compression curve close to these pressures, which are also associated with electronic topological transitions determined from first-principles calculations. Independent in-situ x-ray powder-diffraction determinations of melting for Cd show departures from Lindemann predictions above 1 GPa, consistent with the occurrence of electronic topological transitions.