SYNTHESIS, STRUCTURAL CHARACTERIZATION AND MAGNETIC-PROPERTIES OF -LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-17+ -2, S-THAN-OR-EQUAL-TO-Y-LESS-THAN-OR-EQUAL-TO-9+/-2), A NEW FLUORITE-RELATED OXYNITRIDE/

A series of crystalline Gd-W oxides, with Gd:W ratios spanning the val ues 0.1-3.5, has been prepared and treated with a flow of NH3(g) in th e temperature range 700-1100 degrees C. Besides the previously reporte d formation of GdWO3N and Gd2WO3N2, the following new results were obt ained: (i) cubic Gd0.1WO3 upon ammonolysis forms an (oxy)nitride Gd0.1 W(O,N)(y) with an f.c.c. lattice; (ii) the previously described Gd2WO3 N2 exhibits a solid solubility range Gd3-xW1+x(O,N)(y) with, approxima tely, 0 less than or equal to x less than or equal to 1; (iii) ammonol ysis of Gd14W4O33 yields an oxynitride, the composition of which varie s with the synthesis temperature according to Gd14W4O33-xNy(O less tha n or equal to x less than or equal to 17+/-2, 0 less than or equal to y less than or equal to 9+/-2). All strong diffraction lines, includin g those of the pure oxide (x = y = 0), can be indexed with a body-cent red monoclinic unit cell derived from that of fluorite. For Gd14W4O33 the cell 3 parameters are a = 5.3592(11), b = 3.7295(7), c = 3.8636(8) Angstrom, beta = 92.170(2)degrees and V = 77.17 Angstrom(3). However, strong superstructure reflections in the electron diffraction pattern s indicate that the true unit cell is considerably larger. A partial s tructure determination of Gd14W4O33-xNy has been carried out by the Ri etveld method. Magnetic susceptibility measurements in the temperature interval 15-300 K show a Curie-Weiss law behaviour for Gd14W4O33-xNy, with mu(eff) = 8.08+/-0.06 Bohr magntons per Gd3+ and theta = -12.4+/ -1.1 K for all compositions.