Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5441391 | Journal of Non-Crystalline Solids | 2017 | 6 Pages |
Abstract
A first-order polyamorphic (amorphous-amorphous) phase transition is often observed in amorphous materials that have a tetrahedral structure, such as ice, carbon, or silicon, but it has yet to be observed in amorphous boron nitride (a-BN). We investigated the existence of a first-order phase transition in a-BN by means of first-principles molecular dynamics (MD) simulations at a constant temperature and various pressures. At 300Â K, the volume of a-BN gradually decreases at applied pressures of 0 to 18Â GPa; it then rapidly decreases by about 3% at pressures of 18 to 24Â GPa, providing evidence of a first-order phase transition. The structure remains amorphous throughout the transition. As the pressure is released from 24 to 0Â GPa, the volume gradually increases with preservation of the difference at the phase transition, showing that the structure of the high-density phase is maintained at 0Â GPa. An analysis of the coordination number revealed that a-BN consists mainly of sp2-hybridized BN bonds at 0Â GPa. At the phase transition, sp2 bonds are rapidly converted into sp3 bonds, which subsequently account for about 30% of all bonds. This mechanism resembles that of the phase transition of amorphous carbon, in which the conversion rate is almost 100%. The low conversion rate in a-BN is probably attributable to the relative inflexibility of the structure.
Keywords
Related Topics
Physical Sciences and Engineering
Materials Science
Ceramics and Composites
Authors
Wataru Hayami,