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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