Synthesis and Crystal Structure of a New Oxysulfide Gd6+xTi4 –xS10 – yO6+y (where x ~ 0.04 and y ~ 0.27)

Abstract

A new phase in the quaternary system Gd/Ti/S/O was obtained from a mixture of Gd2O3, Gd2S3, TiO2, TiS2 and Ti by a solid state reaction at 1323 K in a sealed fused-silica tube. The structure of Gd6+xTi4−xS10−yO6+y (where x ~ 0.04, and y ~ 0.27), was solved by single-crystal X-ray diffraction, with R(obs) = 2.69% for 2391 reflections (I > 3σ (I)) and 155 variables. This compound crystallizes with four formula units in the orthorhombic space group Pnma, and the lattice constants (Å ): a = 13.991(1), b = 3.7124(2), c = 34.029(3) Å. The structure is built up from the stacking of ribbons of five Gd-polyhedra alternating with ribbons of five Ti- and Gd/Ti-polyhedra along the a-axis. This is the first example of a rare earth (RE) and titanium oxysulfide compound that shows mixed RE/Ti sites together with pure RE- and Ti-sites. Gd6+xTi4−xS10−yO6+y is a mixed-valent titanium oxysulfide in which half of the Ti cations are Ti3+ and half are Ti4+.