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

Hydrogen storage properties of Nb-x(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 Nb-x(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. (C) 2019 Elsevier B.V. All rights reserved.