Abstract
A compound richer in Ga, VGa2, was formed on the surface of V tapes dipped into a molten Ga bath. By heat treatment at 700°C the VGa2 was changed to V3Ga2 and then V3Ga was formed by diffusion between the V3Ga2 and the V substrate. Effects of Cu additions to the Ga bath and Cu plating before the heat treatment on the diffusion process were studied using optical metallography and electron probe microanalysis. Superconducting transition temperatures of the tapes were also measured.
Without Cu addition, diffusion between V3Ga2 and V proceeds through grain boundaries. By the Cu addition, the diffusion mode changes to bulk diffusion and formation rate of the V3Ga is increased by one order of magnitude. By the Cu plating before the heat treatment the diffusion is also much enhanced. The plated Cu layer rapidly absorbs Ga from the VGa2 and V3Ga2 compounds and Cu diffuses into the compounds. The main reason for the enhancement of the diffusion seems to be the lowering of melting points of VGa2 and V3Ga2 by the Cu addition. The Cu does not penetrate into the V3Ga and makes the formation of V3Ga much easier without deteriorations of the intrinsic superconducting properties.
