Crystal structure and phase transitions of the lithium ionic conductor Li3PS4
Abstract The crystal structures of and phase transitions in the lithium ionic conductor, Li3PS4, which is part of the thio-LISICON (LIthium Super Ionic CONductor) family, were studied using high-temperature synchrotron X-ray diffraction measurements and thermal analysis. There are three transitions among the α, β and γ-phases of this material as a function of temperature. The low-temperature γ-phase transformed to the medium-temperature β-phase at 573 K, which then transformed to the high-temperature α-phase at 746 K. The γ-phase is iso-structural with β-Li3PO4 (SG: Pmn21) with an orthorhombic cell with a = 7.70829(11), b = 6.53521(10), and c = 6.1365(7) A at 297 K. The β-phase has an orthorhombic cell with a = 12.8190(5), b = 8.2195(4), and c = 6.1236(2) A at 637 K. The apexes of the PS4 tetrahedron are ordered in the same direction in the γ-phase, while in the β-phase, they are ordered in a zig-zag arrangement. The γ-phase showed an ionic conductivity of 3.0 × 10− 7 S cm− 1 with an activation energy of 21.3 kJ mol− 1 at room temperature. The β-phase showed an ionic conductivity of 3.0 × 10− 2 S cm− 1 at 500 K with an activation energy of 15.5 kJ mol− 1.