Mechanisms for the reconstructive phase transition between the B1 and B2 structure types in NaCl and PbS -: art. no. 174111

Three possible mechanisms for the reconstructive phase transition from the B1 to the B2 structure types are examined: (1) a modified Buerger (MB) pathway, (2) the Watanabe (W) pathway, and (3) a new pathway (T) proposed by Toledano [Phys. Rev. B 67, 144106 (2003)]. We use first-principles energy calculations to obtain barrier heights for these pathways in NaCl and in PbS. In both NaCl and PbS, the barriers for the MB and T pathways are approximately equal. In NaCl, the barrier for the W pathway is somewhat higher. Both the MB pathway and the T pathway pass through an intermediate B33 structure type. As a result, the fact that a stable B33 intermediate structure is actually observed in PbS does not favor the T pathway over the MB pathway. We also examine experimentally obtained relations between the orientations of the B1 and B2 structures and conclude that they do not definitively favor any pathway over the others.