Role of Nb in Improving the Cyclic Stability of V-Ti-Cr Alloys

抄録

The degradation of reversible hydrogen storage capacity of V-Ti-Cr alloys can be greatly reduced by dissolving a small amount of Nb, yet the exact role of Nb in improving cyclic stability is not known. In this study, we have investigated local structural changes in V_0.25Ti_0.25Cr_0.5H₂ and V_0.25Ti_0.25Cr_0.45Nb_0.05H₂ during hydrogen cycling using the X-ray atomic pair distribution function and the extended X-ray absorption fine structure spectra to understand the effect of Nb. Our study suggests that during hydrogen cycling large Ti atoms are dragged to dislocation cores to reduce strain induced by dislocations. This leaves Ti-poor regions near dislocations for which higher hydrogen gas pressure is required for hydrogen uptake. It is most probable that Nb prevents the segregation of Ti.