Structural changes of wurtzite-type and zincblende-type boron nitrides by shock treatments

Abstract

Wurtzite-type boron nitride (w-BN) and zincblende-type boron nitride (z-BN) powders were shock-treated in the pressure range of 60 to 200 GPa to clarify their polymorphic transformations. The recovered BN powders revealed the effects of the shock wave and residual temperature on phase transition of BN. W-BN was partly transformed to z-BN by shock compression at a pressure of about 100 GPa. At pressures greater than 100 GPa, portions of the w-BN and z-BN powders changed into the BN having a turbostratic structure. Subsequently, this form was crystallized to graphite-like BN (g-BN) and a new form of BN due to high residual temperatures. This new BN modification, probably stabilized by the high surface energy associated with its fine crystallite size of less than 50 nm, was identified as fcc structure with a lattice parameter ofa ₀ = 0.8405 nm. The transformation of z-BN to w-BN was not detected in this post-shock study, as was observed in static high pressure studies.