Heterophase fluctuations of incommensurate omega phase in Cu-Zn system

A heterophase fluctuation of omega ((omega)) phase in the body-centered cubic matrix is studied by evaluating the reciprocal free energy modulus which includes the properties of coherent strain energy and the bulk free energy change. As a consequence, analytical expressions are obtained for the concentration, dimensions and distribution of heterophase (omega) clusters. The incommensurate (omega) cluster having a dual phase ((omega) and (beta)) structure is suggested to form in the heterophase fluctuation. On the basis of the theoretical analysis of the distribution of (omega) clusters, quantitative calculation of diffuse intensity of X-ray diffraction was carried out for the Cu-Zn system. The estimated diffuse intensities I(h)/I0 are in good agreement with the experimental results: the offset of the diffuse intensity peak and ellipsoidal shape of the intensity having streaks towards the nearest fundamental spot. The diffuse peak of X-ray diffraction is manifested to behave like a central phonon peak of heterophase fluctuation as T/(T - T0) where T0 is the coherent transformation temperature.