Evaluation of the sites occupied by Ti in the TiVFeZr multicomponent alloy with C14-type laves phase structure

Hydrogen is an energy vector and if associated with renewable energy sources becomes a reasonable solution for the next generation and storage of energy. Metal hydrides can improve the density of stored energy, since hydrogen is a low-density gas. Among metal hydrides, multicomponent intermetallic metal hydrides have been intensively studied. The most common intermetallic phase found in metal hydrides is the AB2 C14-type Laves phase. A-type atoms (4f) are larger than B-type atoms (B1: 2a and B2: 6h), so that the structure presents three interstices to store hydrogen: A2B2, AB3 or B4. From a hydrogen store perspective, the A-type elements are frequently hydride-forming elements, such as Ti, Zr and V, while B-type non-hydride forming elements, such as Fe. In the case of the equiatomic TiVFeZr multicomponent alloy previously reported by the candidate, from the structure point of view, Ti and Zr occupies A-type sites and V and Fe B-type sites. C14-type Laves phase alloys typically absorb a maximum capacity of about 1 H/M (hydrogen to metal ratio). However, the TiVFeZr alloy absorbs 1.5 H/M, consequently, to maintain the stoichiometric of the alloy due to the measured composition and the larger capacity, Ti must occupy both A and B sites activating more interstices, which can only be determined by neutron diffraction. In this context, determining whether Ti occupies both sites using GEM line will improve our thermodynamic model for C14-type Laves phase alloys for hydrogen storage.