Changing the bond graph—reconstructive phase transitions

5 Changing the bond graph—reconstructive phase transitions 

Reconstructive phase transitions occur when major changes are made in the topology, i.e. when the bond graph is reorganized. The transitions usually observed in structures with lattice-induced strain are displacive and often second order (no latent heat). Reconstructive transitions arise when two quite different structures with the same composition have similar free energies. Unlike the displacive transitions they involve the dissolution of one structure and the recrystallization of a quite different structure. These phase transitions possess a latent heat and often display hysteresis. 

Conceptual reconstructive transitions can be valuable in modelling in cases where a proposed high-symmetry structure is so excessively strained that a drastic rearrangement of the bonds is needed. As an example consider the high-symmetry bond graph of CaCrFs (10286, Fig. 12.6(a)) drawn by connecting Cr to each of the five F ions, with one bond doubled to give the expected six 

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