Rare-earth indium selenides RE 3InSe6 (RE = La−Nd, Sm, Gd, Tb): Structural evolution from tetrahedral to octahedral sites

Highlights: • Selenides RE₃InSe₆ (RE=La−Nd, Sm, Gd, Tb) were obtained by reaction of elements. • Stacks of In-centred tetrahedra gradually evolve to chains of edge-sharing octahedra. • The compounds are semiconductors with optical band gaps of 1.2–1.4eV. 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 1.2–1.4eV. Magnetic measurements indicated that La₃InSe₆ is diamagnetic and Nd₃InSe₆ is paramagnetic with no transitions occurring down to 2K.