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 P1, 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 (1)(∞)[MLnTe(5)](4-) chains built from LnTe(6) octahedra and MTe(4) (M = Ga, In) tetrahedra, but the connectivity between the LnTe(6) octahedra and MTe(4) 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 Ba(2)InSmTe(5) deviates from the Curie-Weiss law. In addition, electronic structure calculation on Ba(2)MYTe(5) (M = Ga, In) indicates that they are both direct-gap semiconductors with large nonlinear-optical coefficients.