Synthesis, structure, and ionic conductivity of solid solution, Li10+δM1+δP2−δS12 (M = Si, Sn)

Abstract

Solid solutions of the silicon and tin analogous phases of the superionic conductor Li₁₀MP₂S₁₂ (M = Si, Sn) were synthesized by a conventional solid-state reaction in an evacuated silica tube at 823 K. The ranges of the solid solutions were determined to be 0.20 < δ < 0.43 and −0.25 < δ < −0.01 in Li_10+δM_1+δP_2−δS₁₂ (0.525 ≤ k ≤ 0.60 and 0.67 ≤ k ≤ 0.75 in Li_4−kM_1−kP_kS₄) for the Si and Sn systems, respectively. The ionic conductivity of these systems varied as a function of the changing M ions: the Si and Sn systems showed lower conductivity than the Ge system, Li_10+δGe_1+δP_2−δS₁₂. The conductivity change for different elements might be due to the lattice size and lithium content affecting the ionic conduction. The relationship between ionic conduction, structure, and lithium concentration is discussed based on the structural and electrochemical information for the silicon, germanium, and tin systems.