Abstract
Realization of the vulnerability of current rechargeable battery systems drives the research of solid electrolytes. In the search for a new Li ion conductor, we explore the rich crystal chemistry of Li 4 Zn(PO 4) 2 which presents a low temperature monoclinic (α-) and a high temperature orthorhombic (β-) polymorph. We solved the crystal structure of the β-phase and found that it has a disordered Li/Zn-sublattice while showing the largest conductivity; however it could not be stabilized at room temperature by quenching. We discovered that the partial substitution of Zn 2+ with Ga 3+ in Li 4-x Zn 1-x Ga x (PO 4) 2 first leads to an intermediate β' phase. Increasing the Ga content to 0.5 mol pfu. enables to stabilize the pure β-phase at room temperature, which exhibits a conductivity by several orders of magnitudes higher than the pristine sample. The crystal structures of the new β'/β-phases have been solved to elucidate the conduction mechanism, which confirms the high sensitivity of ionic conductivity on disorder.