CPM Seminar

An effect of the misfit elastic energy on the thermodynamics of the weakly discontinuous solid-state phase transitions is analyzed within the Landau theory. The phase diagram in the coordinates of temperature, hydrostatical pressure and symmetrized shear strain is presented and the critical points are identified. The effect of external pressure on the associated anomalies of the specific heat, isothermal compressibility and linear thermal expansion coefficient is analysed. Role of fluctuations is considered and the criteria of the Landau theory applicability to the solid-state phase transitions are found. The model is shown to be relevant to a proper ferroelastic phase transition ("thermo-elastic martensite") as well as to orientational ordering transition in crystalline fullerenes.

The thermodynamics of two-phase coherent equilibrium is also analyzed. The contribution to the Gibbs free energy associated with an elastic distortion of the matrix of parent phase by the inclusion of product phase is considered. It is found that the phase transformation proceeds in a finite temperature region with the equilibrium volume fraction depending on temperature rather than at a fixed temperature as it would be expected from the Gibbs phase rule for the first-order transition. An available experimental data is shown to support suggested mechanism for the "athermal" kind of martensitic transition and for the equilibrium phase coexistence in the epitaxial films of MnAs on GaAs.

Thursday, November 1st 2001, 15:30
Ernest Rutherford Physics Building, room 115