Effect of H-induced microstructural changes on pressure-optical transmission isotherms for Mg-V thin films

摘要

Although neither V nor Ti is supposed to mix with Mg, in thin films some alloy formation is observed. On hydrogenation, these alloys show clearly different behaviors. Films of Mg-V disproportionate during repeated absorption and desorption of hydrogen, in contrast to Mg-Ti thin films which are structurally reversible upon several hydrogenation cycles. Using Hydrogenography on co-sputtered Mg-V thin films, we observe the progressive segregation of Mg and V atoms induced by the formation of the respective hydrides. A simple multi-site lattice-gas model with long range H-H interaction reproduces well the optically measured isotherms and allows to determine the evolution of the chemical short-range order parameter s with cycling. The complex features observed in the isotherms are related to micro-structural changes in the film. This paper shows how hydrogenography, being an optical technique, allows us to determine thermodynamic and structural/compositional information for a very large number of metal hydrides simultaneously.