Synthesis, structure and properties of the oxychalcogenide series A4O4TiSe4 (A=Sm, Gd, Tb, Dy, Ho, Er and Y)

AbstractSeven oxyselenide materials have been synthesised with composition A4O4TiSe4 (A=Sm, Gd–Er, Y) via solid state reactions of A2O3, TiSe2 and Se at 900°C. They are all isostructural with Gd4O4TiSe4. Structures have been refined from powder X-ray diffraction data and have monoclinic C2/m symmetry with unit cell parameters of a≈15.7Å, b≈3.75Å, c≈9.65Å and β≈117.5°. They contain infinite ribbons of edge-sharing A4O and A3TiO tetrahedra 4 units wide, which are linked by chains of TiSe4O2 edge-sharing octahedra. Compositions A=Gd–Ho, Y are semiconductors with conductivities 1–3Sm−1 at 300K, with electronic band gaps of between 0.25 and 0.37eV. Magnetic susceptibility is reported from 1.8K to 300K for compositions A=Gd–Ho. Rare earth moments appear to order antiferromagnetically at low temperatures with Gd and Tb showing evidence of ferromagnetism due to spin canting over a narrow temperature range close to TN