Synthesis and Lithium-ion Conductivity of Sr(La1-xLi3x)ScO4 with a K2NiF4 Structure

K2NiF4-type oxides are expected to be potential lithium-ion conductors because they have a structure similar to that of perovskites, which provide a reasonably flexible framework for accommodating defects such as charge carriers within the lattice. However, the K2NiF4-type structure as a framework for lithium conductors is scarcely reported. This article presents the preparation of Sr(La1-xLi3x)ScO4 with a K2NiF4 structure by a solid-state reaction at a high pressure of 2 GPa, and elucidates its lithium-ion-conducting properties. Sr(La1-xLi3x)ScO4 forms solid solutions in the x range of 0.05-0.20. Its orthorhombic lattice expands with lithium doping, indicating the incorporation of lithium ions as interstitial species in the structure. The highly doped samples exhibit high ionic conductivities (e.g., 4.66 x 10(-6 ) S cm(-1) at 250 degrees C for x = 0.15 and 4.29 x 10(-2) S cm(-1) at 375 degrees C for x = 0.2) with an activation energy of similar to 100 kJ mol(-1). The samples show an abnormal increase in the ionic conductivity at similar to 300 degrees C, possibly due to the increase in the orthorhombicity of Sr(La1-xLi3x)ScO4. As the electronic conductivities of the developed oxide materials are a few orders of magnitude lower than their total conductivities, they can be used as solid electrolytes in all-solid-state lithium batteries. The study reveals that K2NiF4-type oxides are attractive candidates for developing novel lithium-ion conductors. (C) The Author(s) 2021. Published by ECSJ.