The thermodynamic properties of disorder CuZn solid solution and nonstoichiometric Cu-Zn alloy: Pseudo-atomic lattice inversion potential method

Abstract In the process of heating, atomic thermal motion causes an increase in Cu or Zn anti-sites and the degree to which atoms randomly occupy sublattices. The disordered solid solution can be separated into partially disordered and fully disordered solid solutions, and the transition from a fully ordered structure to a fully disordered structure of the solid solution should occur as an evolutionary process of atoms that randomly occupy sublattices to different degrees. In this paper, the concept of “disorder degree” is proposed, and a pseudo-atomic lattice inversion potential method is used to simulate the order to disorder transition of CuZn solid solution. The potential parameters can be obtained using density functional theory (DFT) calculation and Chen's lattice inversion method. The results indicate that the lattice distortion exhibits a quadratic relationship in which the disorder degree weakens the cohesive energy in the order-disorder transition process. The calculated vibrational entropy difference between the fully ordered B2 and fully disordered A2 CuZn solid solution is 0.24 kB/atom. Furthermore, a new pseudo-atom γ-(Zn or Cu) system is built to calculate the thermodynamic properties of a non-stoichiometry Cu-Zn alloy system, and the results show that the vibrational entropy, specific heat capacity, and bulk modulus exhibit an approximately linear change with Zn concentration. The vibrational entropy and bulk modulus are sensitive to the phase transition, and the slope mutation facilitates the determination of the phase boundary.