Hydrogen storage properties of Nb-based solid solution alloys with a BCC structure

Abstract Hydrogen storage properties of Nbx(Ti0.7Cr0.3)1-x (x = 0.3, 0.4, 0.5, 0.6) alloys with a body centered cubic (BCC) structure and the crystal structure of their hydrides were investigated. These alloys absorbed hydrogen up to around 1.8 H/M by forming a di-hydride phase in the absorption process, and desorbed to 0.8 H/M to transform to a mono-hydride phase during the desorption process. These behaviors are similar to those of Ti–Cr–V and Ti–Cr–Mo alloys with the BCC structure. XRD patterns indicated that the alloys transformed to the mono-hydride with a slightly distorted BCC structure (orthorhombic structure), and then to the di-hydride with a CaF2 structure. With increasing Nb content, both the lattice constants for all phases, and the equilibrium pressures for the absorption and desorption processes increased. This indicated that Nbx(Ti0.7Cr0.3)1-x does not follow the well-known relationship of equilibrium pressures decreasing with increasing lattice constants. However, the logarithmic equilibrium pressures had a linear relationship with their estimated bulk modulus.