SYNTHESIS AND CHARACTERIZATION OF QUATERNARY SULFIDES WITH THCR2SI2-TYPE STRUCTURE - KCO2-XCUXS2 LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1.5) AND ACOCUS(2) (A=K, RB, CS)

Synthesis, electrical, and magnetic properties of new quaternary alkal i metal mixed-transition metal sulfides [ACoCuS(2) (A = K, Rb, Cs) and KCo2-xCuxS2 (0.5 less than or equal to x less than or equal to 1.5)] are reported. The synthesis was accomplished by sulfurization of a mix ture of corresponding alkali metal carbonate and copper and cobalt oxi des. All of the phases form in the tetragonal ThCr2Si2-type structure in space group I4/mmm. The electrical resistivity measurements show th at the new phases are semiconducting, with room temperature resistivit ies rho(RT) similar to 10(-2) Omega . cm; KCo0.5Cu1.5S2 is metallic wi th a metal-to-nonmetal transition at similar to 120 K. Seebeck measure ments indicate that the majority of charge carriers are holes. The tem perature dependence of magnetic susceptibility shows an anomalous tran sition to the ferromagnetic state in the ACoCuS(2) phases. The electri cal and magnetic properties of the new quaternary phases are compared with those of ternary ACo(2)S(2) (A = K, Rb, Cs). (C) 1996 Academic Pr ess.