Synthesis, crystal structure, and electrical properties of a new quaternary manganese mixed sulfide, BaLa₂MnS₅

A new quaternary sulfide, BaLa₂MnS₅, was prepared by the reaction of CS₂ with a mixture of BaCO₃, La₂O₃, and MnO₂ at 1323 K. The crystal structure of this compound is tetragonal with space group I4/mcm. The lattice parameters are a = 8.014(2) and c = 13.867(3) Å. The refinement of the diffraction data was carried out by the Rietveld method yielding (Ba_1/3,La_2/3) in 4a (0, 0, 1/4) and 8h (0.1620, 0.6620, 0), Mn in 4b (0, 1/2, 1/4), S(1) in 4c (0, 0, 0), and S(2) in 16l (0.1514, 0.6514, 0.6352). The final reliability factors were R_wp = 13.22, R_p = 9.91, R₁ = 2.94, and R_F = 1.82%. The interatomic distance showed a deviation according to the bonds giving distances longer or shorter than the crystal radius sums, which suggests the existence of some covalency in the crystal. The electrical conductivity and Hall coefficient were measured using the van der Pauw method in a temperature range from 18 to 300 K. The electrical conductivity was on the order of 10² Sm^-1, and it increased with increasing temperature showing that BaLa₂MnS₅ is semiconductive. The negative Hall coefficient indicated that the conduction is n-type. The activation energy of conduction was 16 meV above 200 K.