Ni interdiffusion coefficient and activation energy in Cu ₆Sn ₅

Ni diffusion in Cu ₆Sn ₅ intermetallic compound was investigated. First, we successfully fabricated preferred-orientation Cu ₆Sn ₅ crystal by liquid-phase electroepitaxy (LPEE). Then, Ni/Cu ₆Sn ₅ diffusion couples were produced by sputtering from a Ni thin film onto the Cu ₆Sn ₅ crystal. Ni/Cu ₆Sn ₅ diffusion couples were annealed at different temperatures of 120°C, 160°C, 200°C, 255°C, 290°C, and 320°C for 2 h in a vacuum. The Ni atomic profile across the Ni/Cu ₆Sn ₅ interface was obtained by electron spectroscopy for chemical analysis (ESCA). From the Ni atomic profiles, the Matano method was used to evaluate the Ni interdiffusion coefficients (D _Ni) in the Cu ₆Sn ₅ crystal obtained with different annealing temperatures, which then yields the activation energy for Ni diffusion in the Cu ₆Sn ₅ crystal at a particular Ni content. We found that, as Ni diffuses in the ternary Cu _6-x Ni _x Sn ₅ compound phase, the activation energy of Ni interdiffusion decreases with the Ni content.