Abstract
The ternary rare-earth indium selenides RE3InSe6 have been prepared by reactions of the elements at 850 °C and the range of rare-earth substitution has been determined to be RE = La−Nd, Sm, Gd, Tb. Single crystals of La3InSe6, Ce3InSe6, and Nd3InSe6, obtained in the presence of KBr flux, were analyzed by X-ray diffraction, which revealed an orthorhombic structure in space group Pnnm with Z = 4 and cell parameters of a = 14.4722(18)−14.2793(11) Å, b = 17.636(2)−17.4401(14) Å, and c = 4.2123(5)−4.1013(3) Å. The structure consists of two types of linear stacks built from In-centred polyhedra, which are separated by the RE cations in seven and eightfold coordination. Careful examination of the In sites shows that there is a gradual evolution from the noncentrosymmetric La3InS6-type (space group P21212, adopted by most of the sulfides RE3InS6) to the centrosymmetric U3ScS6-type structure (space group Pnnm, adopted by most of the selenides RE3InSe6). Diffuse reflectance spectroscopy showed that all members of RE3InSe6 are semiconductors with optical band gaps of 1.2–1.4 eV. Magnetic measurements indicated that La3InSe6 is diamagnetic and Nd3InSe6 is paramagnetic with no transitions occurring down to 2 K.
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