PHASES IN THE ZRXTA1-X(O,N)Y SYSTEM, FORMED BY AMMONOLYSIS OF ZR-TA GELS - PREPARATION OF A BADDELEYITE-TYPE SOLID-SOLUTION PHASE ZRXTA1-XO1-X, SS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1(XN1)

Phase formation in the system ZrxTa1-x(O,N)y has been studied by ammon olysis of Zr-Ta gels, prepared by the sol-gel technique, at temperatur es between 700 and 1000-degrees-C. The starting gels and observed phas es were characterised by X-ray powder diffraction (XRPD), scanning and transmission electron microscopy (SEM and TEM) and thermogravimetric (TG) analysis. Oxynitride phases of compositions ZrxTa1-xO1+xN1-x, 0 l ess-than-or-equal-to x less-than-or-equal-to 1, with the baddeleyite-t ype structure, were prepared at 800-degrees-C. The unit-cell volume in creased linearly from 127.8 angstrom3 for TaON (x = 0) to 140.9 angstr om3 for ZrO2 (x = 1). The structure was verified for the composition Z r0.4Ta0.6O1.6N0.4 (x = 0.4) by a Rietveld refinement (R(F) = 3.5%) usi ng Cu-Kalpha1 XRPD data. An orthorhombic oxynitride phase was observed in preparations at 700-degrees-C for 0.26 less-than-or-equal-to x les s-than-or-equal-to 0.90 in ZrxTa1-xO1+xN1-x. Unit-cell parameters and powder X-ray reflection intensities agree with an orthorhombic ZrO2 ty pe structure. According to X-ray data, a cubic solid solution phase wi th a fluorite related subcell is present in materials prepared at 900- degrees-C for 0.26 less-than-or-equal-to x less-than-or-equal-to 0.68. However, electron microdiffraction patterns suggest a metrically mono clinic unit cell with a = 6.1 angstrom, b = 14.1 angstrom, c = 7.1 ang strom and beta = 125-degrees. The Ta3N5 type of structure was found to incorporate up to ca. 18 atom% Zr at 900 and 1000-degrees-C.