First-principles density functional calculation of mechanical, thermodynamic and electronic properties of CuIn and Cu2In crystals

► CuIn and Cu2In are crucial interconnect materials for next generation 3D chip stacking packaging. ► Their mechanical, thermodynamic and electronic properties are for the first time studied. ► They are an elastically anisotropic, low stiff and very ductile material and also a conductor. ► Cu2In shows higher elastic anisotropy and stiffness, Debye temperature and heat capacity than CuIn. ► Their heat capacity strictly follows with the T3-law at temperature below the Debye temperature. The study aims at assessing the mechanical, thermodynamic and electronic properties of single-crystalline and polycrystalline CuIn and Cu2In intermetallic compound (IMC) crystals using first-principles calculation based on the density functional theory within the generalized gradient approximation. The lattice constants and the five independent elastic constants of the two hexagonal single crystal structures are first calculated as a function of hydrostatic pressure, and their elastic anisotropy is examined through the computation of the crystal direction-dependent elastic modulus and the Zener anisotropy factor. Subsequently, their associated pressure-dependent polycrystalline elastic properties are also predicted, by which the ductility or brittleness of the IMC materials is characterized. Moreover, the temperature-dependent Debye temperature and heat capacity of these two IMC nanocrystals are determined using a quasi-harmonic Debye model, and their electronic band structures and density of states profiles are examined through analysis of electronic characteristics. The calculation results show that these two IMC crystals are not only an elastically anisotropic, low stiff and very ductile material but also a conductor. The elastic anisotropy, Debye temperature and heat capacity of Cu2In single crystal all surpass those of CuIn, and also, Cu2In crystal tends to be much stiffer than CuIn. Besides, the heat capacity of these two nanocrystals strictly follows with the well-known T3-law at temperature below the Debye temperature and would reach the Dulong–Petit limit at temperature above the Debye temperature.