Theoretical study of the structural stability of CuPd and CuPt alloys: Pressure-induced phase transition of CuPt alloy

CuPd and CuPt have unique aspects in their equilibrium ordered structures. CuPd takes the bcc-based B2 (CsCl-type) structure despite the fcc structure for each constituent metal, while CuPt is the sole example of the L1₁ structure. We demonstrate that the local-density-functional electronic-structure calculation can reproduce the correct stable structures for both compounds among the three ordered phases, B2, L1₁, and L1₀ (CuAu type). Furthermore, a pressure-induced phase transition for CuPt from the L1₁ to B2 structure is predicted. The critical pressure is estimated to be about 41 GPa, but a possible lowering of this value by Cu enrichment is expected. Experimental tests for these predictions are encouraged.