Ga and Ga-based alloys have received significant attention for applications in the liquid state and also for their potential as a bonding material in microelectronic assemblies. This study investigates the phase stability of the CuGa2 phase as a product of the interfacial reaction between liquid Ga and Cu-10Ni substrates at room temperature. In the binary Ga-Cu system, CuGa2 is decomposed into liquid Ga and Cu9Ga4 as the temperature increases to around 260 °C, which prevents the widespread application of this alloy. In contrast to CuGa2 grown from a pure Cu substrate, CuGa2 from the Cu-10Ni substrate shows an increase in the decomposition temperature during heating from 25 to 300 °C. According to our first-principle calculations, there is only a minor difference in the total free energy between Ni solute at the Cu sublattice and the Ga sublattice in the tetragonal CuGa2 crystal structure. This result indicates that both of the sublattices can accommodate the dilute Ni solute with comparable probability. Regardless of the sublattice where the Ni impurities are located, the presence of diluted Ni in the matrix stabilizes the CuGa2 system by inducing some localized Ni 3d states at energy levels near the Fermi level. It is also shown that the formation of Cu antisite defects, which also stabilizes CuGa2, is preferable if the CuGa2 matrix is grown on a Ni-containing substrate.
Keywords: X-ray diffraction; first-principle calculation; intermetallics; phase stability; transmission electron microscopy.