Pressure-Induced Valence Change in Cerium Phosphide

The pressure-volume relationship for cerium monophosphide (CeP) has been determined to 200-kbar pressure. In this range the substance maintains the NaCl-type structure and exhibits abnormal compression. From the data we conclude that there is an electronic transition involving a change in the valence state of Ce from $3^{+}$ towards the $4^{+}$ state near 100-kbar pressure. Qualitative observations of the reflectivity of CeP under pressure support the valence transition. CeP under high pressure may be expected to exhibit superconductivity.