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

Seven oxyselenide materials have been synthesised with composition A(4)O(4)TiSe(4) (A =Sm, Gd-Er, Y) via solid state reactions of A(2)O(3), TiSe2 and Se at 900 degrees 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 approximate to 15.7 angstrom, b approximate to 3.75 angstrom, c approximate to 9.65 angstrom and beta approximate to 117.5 degrees. They contain infinite ribbons of edges-haring A(4)O and A(3)TiO tetrahedra 4 units wide, which are linked by chains of TiSe4O2 edge-sharing octahedra. Compositions A=Gd-Ho, Y are semiconductors with conductivities 1-3 Sm-1 at 300 K, with electronic band gaps of between 0.25 and 0.37 eV. Magnetic susceptibility is reported from 1.8 K to 300 K 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 T-N. (C) 2013 Elsevier Inc. All rights reserved.