Abstract
An extended model of turbostratic stacking faults in hexagonal boron nitride crystals has been presented. In addition to the current state, the proposed model considers tilting in the layers of hexagonal boron nitride paracrystals. Besides reducing the velocity of phonons due to low periodicity in the turbostratic solid, the tilting causes an increase in hardness to 50% higher than that in crystalline material.
In sites of BN crystals where the interlayer distance is shorter than that in perfect hexagonal crystals, a secondary hybridization (spx), to which sp2 was the main contributor but already resembling that in metastable BN (sp3), is suggested for explaining higher hardness of turbostratic materials. The symmetry of four spx orbitals is that of a trigonal pyramid with three basal and one vertex bond.
To verify the proposed turbostratic model, extensive research work must be carried out on detail study of the effect of the crystallinity of layered boron nitride on the phase composition of products of high-pressure phase transformation, especially from the aspect of topology. Moreover, theoretical calculations are desirable to establish the hypothetical secondary hybridization proposed here.
