In-situ X-ray observation of phase transformation of rhombohedral boron nitride under static high pressure and high temperature

Abstract

Abstract In-situ X-ray diffraction study for phase transformation of rhombohedral boron nitride (rBN) to a denser phase was performed under static high pressure (HP) and high temperature (HT) up to 9 GPa and 1600 °C. It was found that the layer stacking sequence of rBN structure began to change at less than 1 GPa, and the phase transformation to wurtzite structure (wBN) was observed at 6–7 GPa and room temperature. After conversion to wBN, further transformation to the zincblend type cubic structure (cubic BN) at 8 GPa and 1400 °C was observed, which is quenchable and the P-T conditions yielding cBN form were similar to that from hexagonal boron nitride. The observed behavior of the phase transformation of rBN by using in-situ X-ray diffraction study is well consistent with the results obtained from the quenching experiment from HP/HT by using belt type HP apparatus. No structural change was observed at 600°C isothermal compression up t0 8GPa, while wBN formation was observed at room temperature compression at 7 GPa. This variation of the transformation behavior under HT isothermal compression may essentially be caused by the reduction of shear stress which affects the rotation and/or slip of hexagonal plane of rBN under HP.