PHASE DIAGRAMS TO HIGH PRESSURES OF UNIVALENT AZIDES BELONGING TO SPACE GROUP D4H18-I4/MCM

The high-pressure phase diagrams of CsN3, TlN3, RbN3, and KN8 were studied by means of differential thermal analysis and volume displacement. These substances decompose explosively near ∼460°C even at high pressures. CsN8, TlN3, and RbN3 each have a new high-pressure transformation with a volume change of ∼3.5% near 6 kbar at 257deg;C. The transition pressures increase with temperature. In the case of CsNs 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.