Compressibility and Electrical Conductivity of Cadmium Sulfide at High Pressures

The compressibility and electrical conductivity of CdS were investigated to over 60 kbar under nearly hydrostatic conditions. Volume change was measured by the inductive-coil technique. In single-crystal samples, the wurtzite {→} rocksalt phase transformation starts at 23±{}1 kbar at 25^∘{}C. At the transition a sudden volume change of 21% occurs, and the electrical resistivity decreases by several orders of magnitude. The average volume compressibilities are 18.2×{}10^-4 kbar^-1 for the wurtzite phase (0-23 kbar) and 9.5×{}10^-4 kbar^-1 for the rocksalt phase (40-60 kbar). Both phases exhibit semiconducting behavior. For the high-resistivity samples used (ρ>10⁵ {Ω} cm), an activation energy of 0.9 eV and a band gap of {}2.3 eV were obtained for the wurtzite phase. Both increase with pressure. For the rocksalt phase an activation energy of 0.1-0.2 eV and a band gap of {}1.3 eV were obtained. The progress of the forward and reverse transitions was followed visually under high magnification, and some observations are made concerning the mechanism of the transformation.