Asymmetric mixing behavior and stability of the predicted phases in the W-Cu system

The W-Cu system is strongly immiscible both in the solid and liquid phases. By combining cluster expansion method with first-principles calculations, present calculations clearly show that there is asymmetric mixing behavior for both FCC and HCP lattices in the W-Cu system. This asymmetric behavior affects the cohesion of the immiscible W-Cu system and is confirmed by Cu/W multilayers ion-bean mixing experiment and Compton scattering observation in the literature. Moreover, the predicted energetically metastable phases of L12 CuW3 and D019 CuW3 are confirmed to be mechanically and vibrationally stable at zero temperature. The further calculated Helmholtz free energy of formation as a function of temperature from lattice dynamics shows that the L12 phase is more stable than D019 phase when temperature is lower than 350 K.