Fluoride-ion conductivity of scheelite-type LiYb1-MF4± (M = Mg, Ca, Sr, Hf)

Fluorite-type fluoride-ion conductors have been widely studied, whereas fluorite-derivative structures remain untapped material spaces as fluoride-ion conductors. In this study, fluoride-ion conductivities in scheelite-type LiYb 1- x M x F 4± x ( M = Mg, Ca, Sr, and Hf) solid solutions were investigated. Introduction of fluorine-vacancy through aliovalent cation-substitution significantly enhanced ionic conductivity, with 15 % Ca 2+ substitution for Yb 3+ exhibiting a maximum conductivity of 1.7 × 10 −5 S cm −1 at 473 K. Structural analysis confirmed the formation of F vacancies, whereas bond valence energy landscape calculations revealed low-barrier conduction pathways. Furthermore, molecular dynamics simulations revealed distinct fluoride migration pathway near the Ca 2+ -doped and undoped regions. These findings offer new insights into the fluoride-ion conduction mechanisms in fluorite-related structures. • Aliovalent cation-doped scheelite-type fluorides were synthesized via mechanochemical milling. • The introduction of fluorine vacancy enhanced F − conductivity. • LiYb 0.85 Ca 0.15 F 3.85 exhibited an ionic conductivity of 1.7 × 10 −5 S cm −1 at 473 K. • Distinct F − migration pathways, near dopants vs undoped regions, were revealed.