Synchrotron XRD and XAS studies of nanocrystalline ZrO2- Y2O3 solid solutions

FABREGAS ISMAEL OSCAR; N. E. WALSÖE DE RECA; D. G. LAMAS; A. F. CRAIEVICH; FANTINI, M.C.A

Madrid

Congreso; XXII congress and general assembly IUCR; 2011

Because of their excellent mechanical and electrical properties, zirconia-yttria (ZrO2-Y2O3) solid   solutions are being widely investigated, in particular because it is a potential candidate to be   used as electrolyte in solid state oxide fuel cells. An important analysis of these material      properties is related to their dependence on nanoscopic scale and composition. The   crystallographic structure and short range order of a series of nanocrystalline ZrO2-Y2O3 solid   solutions with varying Y2O3 content was studied by synchrotron radiation X-ray diffraction  (XRD) and X-ray absorption spectroscopy (XAS). Powdered samples weres ynthesized by a  pH-controlled nitrate-glycine gel-combustion process. Our XRD results indicate the presence of the t´-form of the tetragonal phase (c/a>1) in samples with up to 8 mol% Y2O3, and the t"-form  (c/a=1) for 10 mol% Y2O3. Notice that in the t"-form the oxygen anions are displaced from their ideal positions in the fluorite type structure of the cubic phase. For solid solutions with Y2O3   contents higher than 11 mol% the cubic phase is observed. The t´/t" and t"/cubic compositional   boundaries were determined to be at (9 ± 1) and (10.5± 0.5) mol% Y2O3, respectively. These  composition limits agree well with those reported by Yashima et al [1] for materials composed of larger (micrometric) crystallites synthesized by arc melting followed by a rapid quenching. The c/a   ratios of the t"-form determined for the nanostructured polycrystals studied here are slightly smaller  than those determined by Yashima et al.[1] for powders composed of larger (micrometric) crystallites. A complementary XAS study of the same ZrO2-Y2O3 solid solutions near the absorption edges of Zr and Y demonstrated that the t"/cubic transition is related to a tetragonal-to-cubic symmetry change of the first oxygen coordination shell around Zr atoms, without any significant changes in the environment of Y atoms.