CVM-based calculation of the Pd-H phase diagram in the high temperature region

By combining the Tetrahedron-Octahedron approximation of the Cluster Variation Method with a phenomenological expression for the atomic interaction energies, the phase diagram of the Pd-H system in the disordered region is calculated. A miscibility gap is confirmed. The phase separation is caused by the configuration-independent atomic interactions originating from elastic interactions. The temperature dependency of the Short Range Order Diffuse Intensity Spectrum is calculated at four special points. It is found that, with decreasing temperature, the short range order diffuse intensity at (1 1/2 0) in k-space is amplified, implying the existence of a chalcopyrite-type (I4(1)/amd) ordered phase at lower temperatures.