Synthesis and characterization of a family of two related quaternary selenides: Na 8Eu 2(Si 2Se 6) 2 and Na 9Sm(Ge 2Se 6) 2

Abstract

In this work, two related quaternary rare earth selenide phases were synthesised using the molten flux method. Na 8Eu 2(Si 2Se 6) 2 crystallizes in C2/ m with cell parameters a = 7.0898(10) Å, b = 12.228(2) Å, c = 7.9499(11) Å, β = 107.427(2)° and V = 657.6(2) Å 3 ( Z = 1). This structure comprises layers of [Eu 2(Si 2Se 6) 2] 8− that are in the (1 1 0) planes; each contains ethane-like (Si 2Se 6) 6− units oriented along c, or perpendicular to the planes. This phase is reminiscent of the family of M 2P 2S 6 well-known layered phases and we prepared the series where the main group metal was Si or Ge and the chalcogen was Se or Te. Na 9Sm(Ge 2Se 6) 2 is a related structure, also crystallizing in C2/ m with cell parameters a = 7.9158(15) Å, b = 12.244(2) Å, c = 7.1048(13) Å, β = 106.99(1)° and V = 658.6(2) Å 3 ( Z = 1). This structure comprises layers of [Sm 2(Ge 2Se 6) 2] 9− similar to the selenosilicate yet contains ethane-like (Ge 2Se 6) 6− units oriented along a, i.e. parallel to the layers. We have investigated the family of solids changing the chalcogen atoms (S, Se and Te) and evaluating how the structure changes with chalcogen and with the tetrelide atom (Ge, Si). In addition to single crystal diffraction studies, Raman, diffuse reflectance UV–vis and photoluminescence measurements (for Eu phases) have been used to characterize these compounds.