Synthesis, structural characterisation and magnetic properties of Gd14W4O33−xNy(0 ⩽ x ⩽ 17 ± 2, 0 ⩽ y ⩽ 9 ± 2), a new fluorite-related oxynitride

Abstract

A series of crystalline Gd-W oxides, with Gd:W ratios spanning the values 0.1–3.5 has been prepared and treated with a flow of NH3(g) in the temperature range 700–1100°C. Besides the previously reported formation of GdWO3N and Gd2WO3N2, the following new results were obtained: (i) cubic Gd0.1 WO3 upon ammonolysis forms an (oxy)nitride Gd11.1 W(O, N)4 with an f.c.c. lattice: (ii) the previously described Gd2WO3N2 exhibits a solid solubility range Gd3−A W1−1(O,N)x with, approximately, (0 ⩽ x ⩽ 1: (iii) ammonolysis of Gd14W4O33 yields an oxynitride, the composition of which varies with the synthesis temperature according to Gd14W4Oin33−yNy(0 ⩽ x ⩽ 17 ± 2, 0 ⩽ y ⩽ 9 ± 2). All strong diffraction lines, including those of the pure oxide (x = y = 0), can be indexed with a body-centred monoclinic unit cell derived from that of fluorite. For Gd14W4O33 the cell parameters are a = 5.3592(11), b = 3.7295(7), c = 3.8636(8) Å, β = 92.170(2)° and V = 77.17 Å3. However, strong superstructures reflections in the electron diffraction patterns indicate that the true unit cell is considerably larger. A partial structure determination of Gd14W4O33−xNx has been carried out by the Rietveld method. Magnetic susceptibility measurements in the temperature interval 15–300 K show a Curie-Weiss law behaviour for Gd14W4O33−xNxN with μeff = 8.08 ± 0.06 Bohr magnetons per Gd3+ and θ = − 12.4 ± 1.1 K for all compositions.