Relation between surface phenomena and phase stability in polymorphism of carbon and boron nitride

To find out the reason of hysteresis in transformations α-BN → γ-BN (graphite-like → wurtzite-like boron nitride), the structure of BN crystal surfaces in considered. A conclusion is made that spontaneous crystal phase transformation will only take place under conditions when: 1)thermodynamic conditions correspond to stability area of the new phase; 2)conditions are sufficient for overcoming the process energy barrier; 3)the stability of the new phase nuclei is ensured; 4)the equality range of the energies of atoms on the surfaces of the two phases is obtained