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

ISMAEL O. FÁBREGAS; DIEGO G. LAMAS; NOEMÍ E. WALSÖE DE RECA; MÁRCIA C.A. FANTINI; ALDO F. CRAIEVICH; ROGÉRIO J. PRADO

JOURNAL OF APPLIED CRYSTALLOGRAPHY

International Union of Crystallography

Lugar: Singapore; Año: 2008 vol. 41 p. 680 - 689

0021-8898

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 pHcontrollednitrate–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. Thet´/t´´ and t´´/cubic compositional boundaries were determined to be at 9 (1) and 13 (1) mol% CaO, respectively. The EXAFS study demonstrated that this transition is related to a tetragonal-to-cubic symmetry change of the first oxygen coordination shell around the Zr atoms.