3. Kinetics of pressure-induced phase transitions

Historically, the classification of phase transitions has been based either on the rate of transformation or on the nature of the crystalline forms encountered (Ehrenfest). For pressure-induced phase transformations, it is perhaps more general to consider two categories of solid-solid transition :

• displacive polymorphic transformations, for which the activation energy is relatively low and the transformation rather rapid. They occur at relatively low temperatures (ambient or lower) and no diffusion processes are involved;

• reconstructive transformations, where activation...