Ab initio study of the structural, thermodynamic and electronic properties of the Cu10In7 intermetallic phase

The physico-chemical properties of the intermetallic phases in the Cu–In system have been a matter of considerable theoretical and experimental interest in connection with, i.a., the application of In–Sn alloys as lead-free micro-soldering alloys. Recently, a new binary compound with the chemical formula Cu10In7 has been detected in a study of the η-phase field. The structure of the Cu10In7 phase has been determined as closely related to that of the Cu11In9 compound occurring in the phase diagram, but no experimental or theoretical information on its electronic structure, thermodynamic and equation-of-state properties has yet been reported. In the present work we report the lattice parameters, bulk modulus, energy of formation from the constituent elements and the electronic structure of the new phase, calculated by applying an ab initio density-functional-theory method. Our calculation technique uses the projector augmented wave potentials and the exchange-correlation functions of Perdew and Wang in the generalized gradient approximation. The present results for the Cu10In7 phase are compared with the experimental data available, and with the trends in structural and thermodynamic properties emerging from ab initio calculations also performed in the present study for various structurally related and neighboring compounds in the Cu–In phase diagram, viz., the ideal B82–Cu2In, B81–CuIn, B82–CuIn2 phases and the Cu11In9 compound.

Research highlights▶ Cu10In7 and Cu11In9 are thermodynamically stable with respect to elements at 0 K. ▶ Cu10In7 phase is more stable than the modelled Cu11In9 compound by only 0.92 kJ/mol. ▶ The present ab initio results reproduce very well the available structural data. ▶ Similar DOS for both phases, the most prominent bonding band comes from Cu-d states. ▶ Enhanced relative thermodynamic stability is predicted for phases with 40–45 at.% In.