Syntheses, Structures, Physical Properties, and Electronic Structures of Ba2MLnTe5 (M = Ga and Ln = Sm, Gd, Dy, Er, Y; M = In and Ln = Ce, Nd, Sm, Gd, Dy, Er, Y)

The 12 new rare-earth tellurides Ba(2)MLnTe(5) (M = Ga and Ln = Sm, Gd, Dy, Er, Y; M = In and Ln = Ce, Nd, Sm, Gd, Dy, Er, Y) have been synthesized by solid-state reactions. The two compounds Ba(2)GaLnTe(5) (Ln = Sm, Gd) are isostructural and crystallize in the centrosymmetric space group P (1) over bar, while the other 10 compounds belong to another structure type in the noncentrosymmetric space group Cmc2(1). In both structure types, there are one-dimensional anionic (infinity)(1)[MLnTe(5)](4-) chains built from LnTe(6) octahedra and MTe4 (M = Ga, In) tetrahedra, but the connectivity between the LnTe(6) octahedra and MTe4 tetrahedra is different for the two structure types. On the basis of the diffuse-reflectance spectra, the band gaps are around 1.1-1.3 eV for these compounds. The Ba(2)MLnTe(5) (M = Ga and Ln = Gd, Dy; M = In and Ln = Gd, Dy, Er) compounds are paramagnetic and obey the Curie Weiss law, while the magnetic susceptibility of Ba2InSmTe5 deviates from the Curie-Weiss law. In addition, electronic structure calculation on Ba2MYTe5 (M = Ga, In) indicates that they are both direct-gap semiconductors with large nonlinear-optical coefficients.