Polymorphous transformations of graphite-like boron nitride of different degree of crystalline perfection under high pressure

For the first time systematic structural study was made on features of BNsub(g) polymorphous transformations of different degree of crystalline perfection under the effect of high pressure at temperatures from room up to 1200 deg C. It is shown that mechanism of polymorphous transformations of graphite-like boron nitride at high pressures as well as their rate and the type of formed modification of BN are determined by the degree of perfection of initial structure. Three-dimensional oredered BNsub(g) structure in 20-1200 deg C range at 11 GPa is subjected to martensite transformation, in result of which wurtzite modification forms. Turbostratic BNsub(g) under the same conditions is characterised by diffuse transformation with formation of sphalerite phase. Both mechanisms of polymorphous transformations are manifested during compression of partly ordered BNsub(g)