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

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 Gd0.1WO3 upon ammonolysis forms an (oxy)nitride Gd0.1W(O, N)x with an f.c.c. lattice; (ii) the previously described Gd2WO3N2 exhibits a solid solubility range Gd3-xW1+x(O, N)y with, approximately, 0≤x≤1; (iii) ammonolysis of Gd14W4O33 yields an oxynitride, the composition of which varies with the synthesis temperature according to Gd14W4O33-xNy(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) A, β=92.170(2) and V=77.17 A3. However, strong superstructure reflections in the electron diffraction patterns indicate that the true unit cell is considerably larger. A partial structure determination of Gd14W4O33-xNy 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-xNy, with μeff=8.08±0.06 Bohr magnetons per Gd3+ and θ=-12.4±1.1 K for all compositions. (orig.)