The fcc - bcc structural transition: II. A mean field model for finite-temperature effects.

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Abstract
We present a model for temperature induced martensitic phase transitions where the excitations leading to the phase instability are local fluctuations of the respective order parameter which describes the displacement of a single atom or an atomic plane when transforming structure A into structure B. The fluctuations of the order parameter are treated in the framework of a Landau - Ginzburg model and allow us to describe the temperature induced first-order phase transition as being driven by strain fluctuations (caused by anharmonicities) rather than by phonon softening. In some materials this phenomenological mean field treatment represents a possible model for martensitic phase transitions.