Abstract

Theoretical calculations of the thermal expansion coefficients of the solder alloy systems Sn–Pb and Sn–Ag were attempted by using a cluster expansion method. Five ordered fcc phases for each system were employed to perform the matrix inversion and to determine the correlation coefficients in cluster expansion formalism. The coefficients of thermal expansion of the ordered alloys were obtained through first-principles electronic structure calculations coupled with a Debye treatment of the vibrating lattice. The correlation functions for disordered alloys were derived through Monte-Carlo simulations. The calculated results are in very good agreement with experiments, indicating the feasibility of using cluster expansion theory for thermal expansion coefficient calculations. This study may provide a simple approach to estimating thermal expansion coefficients of disordered structures.