Structure and Properties of Mixed-valence Compound Eu5Zr3S12

Needle-shaped crystals of Eu5Zr3S12 and Eu3.67Sr1.33Zr3S12 were synthesized by solid-state reactions of the elements and ZrS2 at 673-1273 K in alumina crucibles, and their crystal structures were determined by single-crystal methods. They are isotypic with hexagonal symmetry (space group P (6) over barm, Z = 1, Eu5Zr3S12: a = 1170.7(2), c = 394.27(8) pm, wR2 = 0.0636 for 552 F-2 and 27 parameters; Eu3.67Sr1.33Zr3S12: a = 1167.0(2), c = 395.71(8) pm, wR2 = 0.0887 for 484 F-2 and 29 parameters) and contain one-dimensional chains of edge-sharing ZrS2S4/2 octahedra running parallel to [001]. Two europium sites are seven- or nine-fold-coordinated by sulfur, Eu5Zr3S12 is a Curie paramagnet with all effective magnetic moment of mu(eff) = 13.37(1) mu(B) per formula unit (fu), in agreement with Eu2+/fu. Eu-151 Mossbauer spectra show two absorption lines suggesting a static mixture of Eu2+ and Eu3+ in accordance with Eu-3(2+) Eu-2(3+) Zr-3(4+) S-12(2), This assignment is not in line with the observed Eu-S distances. To resolve this, we suggest pure Eu2+ at the 2c site and inhomogeneous mixed valence ate 3f site according to (Eu-2(2+))(2c)(Eu2+Eu23+)(Zr34+S122-)-Zr-3f. This is supported by the site preference of Sr2- in Eu3.67Sr1.33Zr3S12.