Phase Diagrams to High Pressures of the Univalent Azides Belonging to the Space Group D4h18-I4 / mcm

Abstract

The high‐pressure phase diagrams of CsN₃, TlN₃, RbN₃, and KN₃ were studied by means of differential thermal analysis and volume displacement. These substances decompose explosively near ∼ 460°C even at high pressures. CsN₃, TlN₃, and RbN₃ each have a new high‐pressure transformation with a volume change of ∼ 3.5% near 6 kbar at 25°C. The transition pressures increase with temperature. In the case of CsN₃ this transition line meets the tetragonal/bcc transition line at a triple point at 173°C, 8 kbar. The resulting CsN₃ III/bcc phase boundary was followed to 37 kbar, where it is terminated by explosive decomposition. The TlN₃ tetragonal/bcc boundary was followed to 20 kbar, where it is also terminated. The melting curves of KN₃ and TlN₃ were followed only to ∼ 5 kbar, where they are terminated.