Compressibility of Calcium Nitride to 137 Kb

Abstract

α-Ca₃N₂ as an opaque, red-brown crystalline powder lying in the cubic Ia3 space group, was placed into a specially designed glove box under nitrogen atmosphere, along with powdered fcc Au, and carefully loaded within the β-brass gasket of a conventional high pressure diamond anvil cell (DAC). The powdered samples were then sealed under nitrogen atmosphere to a pressure of 8.4 Kb and taken to Cornell High Energy Synchrotron Source where conventional Debeye-Scherrer diffraction photographs were recorded at 8.4, 91 and 137 Kb. The pressure of the sample was monitored by using the equation of state of Au, and no phase change from the Ia3 structure was observed in the sample of powdered α-Ca₃N₂ up to a pressure of 137 Kb, although the red-brown powder was observed to undergo a slight band gap broadening as the opaque powder became a slightly yellow-like tinged transparent phase above 8.4 Kb. A compressibility curve and a bulk modulus for α-Ca₃N₂ are derived from the data presented herein.