Shear mechanisms of phase transitions in boron nitride

Abstract

The behaviour of rhombohedral modification of boron nitride has been studied under static pressures within the range from 3.5 to 7.7 GPa. At low temperatures when diffusion processes are ruled out a great amount of wurtzite boron nitride was found to form. The analysis of the texture phase relation for compacts prior to and after thermobaric treatment indicates unambiguously that a transformation mechanism is realized which is associated with the splitting of basic layers by buckling. For this mechanism of phase transformation the orientation relation of crystal lattices is as follows

(100)_w//(001)_r; [1100]_w//[0001]_r

which corresponds to texture relations found experimentally.

Key Words:

• rhombohedral boron nitride
• phase transition mechanism
• high pressure
• orientation relation