Syntheses, structures, physical properties, and theoretical study of LaCu0.40Te2, NdCu0.37Te2, SmCu0.34Te2, GdCu0.33Te2, and DyCu0.32Te2

Five rare-earth copper tellurides have been synthesized by the reactions of the elements at 1073 K. The isostructural compounds LaCu0.40Te2 (a = 7.7063(13) Angstrom, b = 8.5882(14) Angstrom, c = 6.3115(10) Angstrom, T = 153 K), NdCu0.37Te2 (a = 7.6349(7) Angstrom, b = 8.3980(8) Angstrom, c = 6.18388(6) Angstrom, T = 153 K), SmCu0.34Te2 (a = 7.6003(10) Angstrom, b = 8.3085(11) Angstrom, c = 6.1412(8) Angstrom, T = 153 K), GdCu0.33Te2 (a = 7.5670(15) Angstrom, b = 8.2110(16) Angstrom, c = 6.0893(12) Angstrom,T = 107 K), and DyCu0.32Te2 (a = 7.5278(13) Angstrom, b = 8.1269(14) Angstrom, c = 6.0546(11) Angstrom, T = 107 K) crystallize with four formula units in space group D-2h(11)-Pbcm of the orthorhombic system. In each, the rare-earth (Ln) atom is coordinated by a bicapped trigonal prism of Te atoms and the Cu atom is coordinated by a tetrahedron of Te atoms. Infinite linear Te(1+x)- chains run parallel to c, with Te-Te distances decreasing from 3.1558(5) Angstrom in LaCu0.40Te2 to 3.0273(3) Angstrom in DyCu0.32Te2. Both the thermopower and conductivity data in the c direction show LaCu0.40Te2 to be a semiconductor at all temperatures, and NdCu0.37Te2, SmCu0.34Te2, and GdCu0.33Te2 to be semiconductors above 150-200 K. The thermopower data for these three compounds exhibit very high peaks of approximately 900 mu V/K in the vicinity of 150 K, followed by a rapid decrease at lower temperatures. This behavior deviates from the trend expected for semiconductors. Huckel calculations predict that the Te(1+x)- chains in LnCu(x)Te(2) should show metallic properties. Possible reasons for this discrepancy between theory and experiment involve distortions of the Te chains or disorder of the Cu atoms. GdCu0.33Te2 is paramagnetic with mu(eff) = 7.74(3) mu(B), typical for Gd3+.