Abnormal Freezing Effect on Electron Conduction of Ball-milled Lanthanum Trihydride for Superionic Conductor

A recent finding shows that lattice deformation could transform the mixed electronic/hydride (H^-) conducting lanthanum trihydride (LaH₃) to a superionic H^- conductor. Such a feature would enable the development of a brand-new all-solid-state hydride ion battery. It is essential to elucidate the mechanism of such a phenomenon. Here, we disclose an abnormal freezing effect on the electronic conductivity (σ_e) of the ball-milled LaH₃; that is, σ_e can be lowered by over 2 orders of magnitude upon a low-temperature treatment. Low-temperature Raman reveals that at low temperatures, lattice deformation has a noticeable influence on the interaction of hydrogen at octahedral (H_o) and tetrahedral (H_t) sites, which may play a crucial role in hindering electron conduction. This freezing effect can significantly improve the ionic transfer number of rare earth-based H^- conductors and provide a new direction to the development of solid electrolytes for low-temperature all-solid-state batteries.