NEW QUATERNARY CHALCOGENIDES BALNMQ3 (LN = RARE-EARTH M=CU,AG Q=S,SE)

The new quaternary compounds BaLaCuQ3 (Q = S, Se) have been synthesized by the reaction of the constituent binary chalcogenides and elements at 1000-degrees-C. The crystal structures have been determined by X-ray diffraction techniques. Crystal data: BaLa CuS3-space group D2h16-Pnma, M = 435.97, Z = 4, a = 11.316(2), b = 4.236(1), c = 11.724(2) angstrom (T = 115 K), V = 562.0(2) angstrom3, R(w)(F2) = 0.059 for 1051 observations and 38 variables, R(F) = 0.019 for 1037 observations having F(o)2 > 2sigma(F(o)); BaLa CuSe3-space group D2h16-Pnma, M = 576.67, Z = 4, a = 11.111(4), b = 4.293(2), c = 13.830(4) angstrom (T = 115 K), V = 659.7(4) angstrom3, R(w)(F2) = 0.129 for 1385 observations and 38 variables, R(F) 0.050 for 1313 observations having F(o)F > 2sigma(F02). The BaLaCuS3 structure has a three-dimensional framework with channels that accommodate barium ions. The lanthanum atoms have monocapped trigonal prismatic coordination and the copper atoms have tetrahedral coordination. BaLaCuSe3 crystallizes into two phases, an alpha phase that is isostructural with BaLaCuS3 and a layered beta phase that is isostructural with Eu2CuS3. The layers, which are separated by Ba2+ ions, consist of edge-sharing octahedral chains and corner-sharing tetrahedral chains. The two structures are closely related and beta-BaLaCuSe3 undergoes a phase transformation to alpha-BaLaCuSe3 upon mechanical grinding. The reverse phase transition occurs when alpha-BaLaCuSe3 is annealed at elevated temperatures. (C) 1994 Academic Press, Inc.