Sm8Se10 (k-phase) was prepared by solid-state reaction followed by chem. transport reaction. It crystd. as tetragonal, space group I41/a, a 1.2000(7), c 1.4075(30) nm, Z = 4, R = 0.071, Rw = 0.067. The coordination polyhedra around the Sm atoms are derived from distorted triangular prisms. A cage 8-membered ring formed by 8 Sm atoms is similar to that of S4N4. The projection of these Sm8 rings along the c direction exhibits a regular array. Structural parameter anal. and elec. resistivity measurements indicate that Sm8Se10 is a mixed-valence rare earth compound

Key words: CRYSTAL STRUCTURE, SOLIDPHASE SYNTHESIS, RARE EARTH, CAGE STRUCTURE