Crystal Structure of γ₂′ Martensite in Au-47.5 at%Cd Alloy

Crystal structure of the γ2′ martensite in a Au-47.5 at%Cd alloy has been analyzed by the single crystal X-ray diffraction method. The lattice constants were a=0.4859(11), b=0.3151(1) and c=0.4766(1) nm. The space group was Pcmm, with 4 atoms in the unit cell as Ölander reported. The structure was refined by the full-matrix least squares method to a final R factor of 4.7%, noticeably improved from that of Ölander. Moreover, the amount of shift of each atom from the ideal stacking positions in the hcp structure was discussed by using a hard sphere model of atoms; e.g. atoms in each layer are not arranged centro-symmetric.