Unravelling the rare-earth (RE) element-induced magnetic and optical properties in the structures of quaternary selenides SrRECuSe3

https://doi.org/10.1016/j.inoche.2023.111183

We report novel selenides SrRECuSe₃ (RE = Nd, Sm, Tb–Yb), which crystal structures complete the series of the whole row of SrRECuSe₃ (RE = Sc, Y, La–Nd, Sm, Gd–Lu). Polycrystalline samples were obtained by reductive selenidation with stepwise heating from 870 to 1070 K. Selenides SrRECuSe₃ (RE = Y, Gd, Lu) were also obtained using the same synthetic approach. The resulting compounds crystallize in two space groups, namely Pnma (RE = Y, Nd, Sm, Gd–Dy) and Cmcm (RE = Sc, Ho–Lu). Both types of crystal structures consist of the RESe₆ octahedra and CuSe₄ tetrahedra but differ in the coordination polyhedron of the Sr²⁺ cation. In SrRECuSe₃ (RE = Y, Nd, Sm, Gd–Dy), the Sr²⁺ cation is characterized by a monocapped trigonal prism, while in SrRECuSe₃ (RE = Sc, Ho–Lu) the coordination environment of Sr²⁺ is described by highly symmetrical trigonal prismatic coordination. Both structural types are formed by layers separated either by chains formed by monocapped trigonal prisms or by alternating chains formed by trigonal prisms. The band gap value of SrRECuSe₃ varies from 1.45 eV to 2.21 eV. Selenides SrRECuSe₃ (RE = Sm, Gd, Tb, Ho, Er, Tm, Yb) at temperatures above 4 K behaves like paramagnets with antiferromagnetic interaction of the RE³⁺ moments. The experimental Curie constants and effective magnetic moments are in good agreement with the calculated ones for RE³⁺ ions excluding Sm³⁺.