Role of defect structure on hydrogenation properties of Zr _0.9Ti_0.1V₂ alloy

The pseudobinary Zr_0.9Ti_0.1V₂ compound was prepared by induction melting method. The microstructure and phase compositions were examined by the scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). Hydrogen absorption pressure composition isotherms (P-C isotherms) were investigated by pressure reduction method using Sievert apparatus at temperature ranging from 673 to 823 K. The compositional homogeneity of the alloy was achieved under the homogenizing treatment at 1373 K for 100 h. Twin defects with {111}<022> orientation relationship were observed in the Zr_0.9Ti_0.1V₂ annealed at 1373 K for 100 h. The phase compositions of the annealed Zr _0.9Ti_0.1V₂ alloy could be attributed to ZrV₂ Laves phase and V BCC solid solution. After hydrogenation, the alloy hydrides were consisted of ZrV₂H_3.6 and V ₄H_2.88. Titanium substitution in the Zr _0.9Ti_0.1V₂ alloy induced the formation of twin defect structures and the multiphase consisting of Laves (C15 type) related with BCC solid solution phases. The especial phase compositions and structures in the alloy were favorable to decrease the equilibrium pressure and improve the hydrogen absorption kinetics due to the twin defects in Zr_0.9Ti _0.1V₂ comparing with the primary ZrV₂ alloy. The desorption hysteresis could be decreased to a certain extent in the Ti-doped alloy under the experimental condition. V-based BCC phase in the Zr _0.9Ti_0.1V₂ alloy could improve hydrogen absorption and desorption properties by an autocatalytic mechanism.