posted on 1999-12-22, 00:00authored byFu Qiang Huang, Paul Brazis, Carl R. Kannewurf, James A. Ibers
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) Å, b = 8.5882(14) Å, c = 6.3115(10) Å, T = 153
K), NdCu0.37Te2 (a = 7.6349(7) Å, b = 8.3980(8) Å, c = 6.18388(6) Å, T = 153 K), SmCu0.34Te2 (a =
7.6003(10) Å, b = 8.3085(11) Å, c = 6.1412(8) Å, T = 153 K), GdCu0.33Te2 (a = 7.5670(15) Å, b = 8.2110(16)
Å, c = 6.0893(12) Å, T = 107 K), and DyCu0.32Te2 (a = 7.5278(13) Å, b = 8.1269(14) Å, c = 6.0546(11)
Å, T = 107 K) crystallize with four formula units in space group D2h11-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) Å in LaCu0.40Te2 to 3.0273(3) Å 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 μV/K in the vicinity of 150 K, followed by a rapid
decrease at lower temperatures. This behavior deviates from the trend expected for semiconductors. Hückel
calculations predict that the Te(1+x)- chains in LnCuxTe2 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 μeff = 7.74(3) μB, typical for Gd3+.