Studies on hydrogen loaded V-Fe8 at% films on Al2O3 substrate

Hydride formation of V-Fe8 at% films with different microstructures was investigated by measuring the electromotoric force (EMF), in-plane stress and, additionally, the local chemistry by performing tomographic atom probe (TAP). The phase boundaries of the films were found to be microstructure dependent: the alpha-phase solubility limit was found to be c(H,alpha) = 0.1 H/V and c(H,beta) = 0.45 +/- 0.02 H/V for films with small-domain size, and c(H,alpha) = 0.1 H/V and c(H,beta) = 0.6 +/- 0.02 H/V for films with large domain size. Stress release also depends on the microstructure; it is more efficient for small-domain samples resulting in smaller total stress. It is shown that the plateau pressure and the plateau slope of the films increase with hydrogen-induced in-plane compressive stress increase. TAP analysis at about 20 K monitors the occurrence of a plate-like hydride VD0.65-precipitate at the V/Pd interface. The detected concentrations are in good agreement with those expected at low temperatures. (C) 2007 Elsevier B.V. All rights reserved.