Amorphous boron nitride at high pressure

Abstract

The pressure-induced phase transformation in hexagonal boron nitrite and amorphous boron nitrite is studied using ab initio molecular dynamics simulations. The hexagonal-to-wurtzite phase transformation is successfully reproduced in the simulation with a transformation mechanism similar to one suggested in experiment. Amorphous boron nitrite, on the other hand, gradually transforms to a high-density amorphous phase with the application of pressure. This phase transformation is irreversible because a densified amorphous state having both sp³ and sp² bonds is recovered upon pressure release. The high-density amorphous state mainly consists of sp³ bonds and its local structure is quite similar to recently proposed intermediate boron nitrite phases, in particular tetragonal structure (P4₂/mnm), rather than the known the wurtzite or cubic boron nitrite due to the existence of four membered rings and edge sharing connectivity. On the basis of this finding we propose that amorphous boron nitrite might be best candidate as a starting structure to synthesize the intermediate phase(s) at high pressure and temperature (probably below 800 °C) conditions.

Keywords:

• Polyamorphism
• boron nitride
• amorphous
• phase transformation

Acknowledgement

The calculations were partially run on TÜBİTAK ULAKBİM, High Performance and Grid Computing Center (TRUBA resources).

Funding

This work was supported by the Scientific and Technical Research Council of Turkey (TÜBİTAK) [grant number 114C100].