Model for the structural changes occurring at low temperatures inPdDx. II. Extension to lower concentrations

The concept of "mixed" microdomains presented in a previous paper for the description of the complicated diffuse intensity contours occurring in ${\mathrm{PdD}}_x$ at low temperaturers for $x>\mathrm{}0.71\mathrm{}$ has been extended to describe the diffuse scattering at lower concentrations, i.e., $x$ near 0.65. A diffuse neutron scattering experiment in Pd${\mathrm{D}}_{0.69}$ is presented and the results in this intermediate-concentration range can easily be explained in the framework of the extended model. The model shows that the simple isointensity contours at lower concentrations can be described by "mixed" microdomains whose components are cells having a (100) mirror plane. The transition to the complicated contours for $x>\mathrm{}0.71\mathrm{}$ occurs when in the composition of the "mixed" domain the contribution of cells asymmetric relative to the (100) plane is progressively increased at higher concentrations.