Synchrotron X-ray powder diffraction and extended X-ray absorption fine structure spectroscopy studies on nanocrystalline ZrO2–CaO solid solutions

I.O. FÁBREGAS; D.G. LAMAS; N.E. WALSÖE DE RECA; M.C.A. FANTINI; A.F. CRAIEVICH; R. JUNQUEIRA PRADO

Osaka - Japon

Congreso; Congress of the International Union of Crystallography; 2008

The crystal structure and the local atomic order of a series of nanocrystalline ZrO2-CaO solid solutions with varying CaO content were studied by synchrotron radiation X-ray powder diffraction and extended X-ray absorption fine structure (EXAFS) spectroscopy. These samples were synthesized by a pH-controlled nitrate-glycine gel-combustion process. For CaO contents up to 8 mol%, the t´-form of the tetragonal phase (c/a > 1) was identified, whereas, for 10 and 12 mol% CaO, the t"-form (c/a = 1; oxygen anions displaced from their ideal positions in the cubic phase) was detected. Finally, the cubic phase was observed for solid solutions with CaO content of 14 mol% CaO or higher. Thus, the t´/t" and t"/cubic compositional boundaries were determined to be at (9 ± 1) and (13 ± 1) mol% CaO, respectively. EXAFS study demonstrated that this transition is related to a tetragonal-to-cubic symmetry change of the first oxygen coordination shell around Zr atoms.