Synthesis, structure and physical properties of layered quaternary sulfides NaLiMS2 (M = Mn, Fe, Co)

Three layered quaternary sulfides, NaLi M S 2 ( M  = Mn, Fe, Co) were synthesized by solid-state reactions. They adopt a trigonal CaAl 2 Si 2 -type structure (S.G. P -3 m 1) with Li and M randomly distributed at the tetrahedral metal site. Magnetic measurements reveal spin-glass ground states for these compounds, in contrast to the long-range antiferromagnetic order in the ternary counterpart NaFe 1.6 S 2 . As evidenced by electrical resistivity and optical measurements , all these three compounds show semiconducting nature, consistent with the results of first-principles calculations. The measured band gaps are 3.4 eV and 1.25 eV for NaLiMnS 2 and NaLiCoS 2 , respectively. Photoelectric measurements on NaLiCoS 2 demonstrate its potential application in photovoltaic devices .