First-principles investigation of the Cu–Ni, Cu–Pd, and Ni–Pd binary alloy systems

• Cu–Ni–Pd binaries can be modelled theoretically by GGA level DFT CE.
• Significant errors can be avoided by updating LDA-DFT to PBE-DFT.
• Small amount of Ni magnetize fcc Pd to 0.26 Bohr magnetons.
• Small amount of Ni should be miscible to Cu even in 0 K.

Phase diagrams of copper–nickel–palladium binary alloys were determined by density functional theory cluster expansion method. The system has both magnetic and non-magnetic binaries and subtle phase coexistence areas between similar and different kind of lattice types. Furthermore, the CuPd binary has several ordered structures. Cluster expansion models were constructed by heuristic cluster selection for all of the fcc structures and for the CuPdbcc structure. Both configurational and magnetic phase diagrams were determined. Small amount of nickel magnetize fcc palladium to 0.26 μB from which the magnetic moment rises almost linearly to that of pure Ni. In CuNi, 0.46 x-Ni is needed for the magnetic transition. In CuPd alloy in 0 K, configurational free energy difference between bcc and fcc lattice resulting to phase separation is only about 1.1 kJ/mol-atoms. Low temperature energetics and magnetic phase diagrams have good quantitative agreement with available experimental and theoretical results. Finite temperature properties of the alloys are in good qualitative agreement with experimental results.