Heterophase fluctuations of incommensurate omega phase in Cu-Zn system

A heterophase fluctuation of omega (ω) 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 ω clusters. The incommensurate ω cluster having a dual phase (ω and β) structure is suggested to form in the heterophase fluctuation. On the basis of the theoretical analysis of the distribution of ω 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.