Pd_2Cd_(11-δ) (0.21≤δ≤0.51)-a partly disordered γ-brass type phase and Pd_(0.238)Cd_(0.762)-a γ-brass related incommensurate phase in the palladium-cadmium system

摘要

The Cd rich part of the Cd-Pd phase diagram was reassessed by means of synthesis and single crystal and powder X-ray diffraction. The region contains two phases that have been reported to have substantial compositional widths, Cd_(11)Pd_2 and Cd_4Pd. The phase Cd _(11)Pd_2 that has previously been reported to be a disordered γ-brass crystallizing is space group P43m is here shown to crystallize in I43m and the mechanism for compositional variation is explained. The phase Pd_4Cd has previously been shown to constitute a phase field or a phase bundle of modulated structures and here we determine the structure of a compound Pd_(0.238)Cd_(0.762) which crystallizes in the orthorhombic superspace group Fmmm(α00)0s0 (F=[(1/2, 1/2, 0, 0); (1/2, 0, 1/2, 0); (0, 1/2, 1/2, 0)] with the fundamental cell dimensions a=4.687(2) ?, b=10.000(1) ?, c=14.140(2) ?, q=0.6432(6)a.