Mechanochemical synthesis of rock salt-type Na2CaSnS4 as a sodium-ion conductor

Abstract

Na₂CaSnS₄ was prepared by mechanochemical synthesis from a mixture of Na₂S, CaS, and SnS₂. The crystal structure was determined from X-ray powder diffraction data. The chemical composition was confirmed by energy dispersive X-ray spectroscopy, and the ionic conductivity was measured using electrochemical impedance spectroscopy. Na₂CaSnS₄ crystallizes with a rock salt-type structure, space group Fmm, a = 5.6842 (3) Å, V = 183.66 (2) ų, and Z = 1. All the cations are statistically disordered over a unique crystallographic site and are octahedrally coordinated to the sulfur atoms. The ionic conductivity of Na₂CaSnS₄ is 4.2 × 10⁻⁸ S cm⁻¹ (E_a = 0.6 eV) at 33 °C.