New Low-Dimensional Quaternary Sulfides NaCuMS2 (M = Mn, Fe, Co, and Zn) with the CaAl₂Si₂-Type Structure: Synthesis and Properties

The synthesis, structure, and electronic properties of a series of new quaternary layered sulfides, NaCuMS₂ (M = Mn, Fe, Co, Zn) are reported. The synthesis was accomplished by sulfurization of a mixture of oxide or sulfide and carbonate precursors of the corresponding metals by nitrogen gas charged with CS₂. All of the phases crystallize in the trigonal CaAl₂Si₂-type structure in space group P3m1. The electrical resistivity measurements show that all of the new phases are semiconducting, with room-temperature resistivities ρ_RT varying from 6.2 × 10^-1 to 5 × 10^-2 Ω·cm, depending upon the transition metal M. The magnetic susceptibility measurements indicate the presence of localized Mn²⁺ ions in NaCuMnS₂. The NaCuMS₂ (M = Fe, Co) phases display temperature-independent paramagnetism, whereas the NaCuZnS₂ phase is diamagnetic as expected. In addition, detailed low-temperature magnetic studies of the NaCuFeS₂ phase revealed spin-glass-type behavior with the freezing temperature T_f ∼ 50 K.