Turbostratal boron nitride under high pressure and temperatures

Direct transformation of boron nitride having turbostratal structure (BNsub(T)), into cubic modification (BNsub(c)) at high pressures and temperatures as compared with direct phase transformation of three-dimensional-ordered boron nitride (BN0) is experimentally investigated. Ordering of BNsub(T) structure under effect of high pressures and temperatures is also investigated. Ordering of the structure of turbostrated boron nitride starts at 1000 K in the 3-5 GPa pressure range and it is completed at 1550 K. Threshold pressure makes up 6 GPa and initial temperature equals 1250 K BNsub(k) formation from the initial turbostratal boron nitride (BNsub(t)); when BNsub(c) is formed from the initial three dimensional-ordered boron nitride (BNsub(o)) pressure is the same and temperature is equal to 1800 K. Wurtzite-like modification results from direct BNsub(o) transformation at lower temperatures. Rate of transformation of the initial BNsub(t) into BNsub(c) is higher than the rate of formation of cubic modification from the initial three-dimensional ordered boron nitride