Positron characterization of metastable phases in Yttria Stabilized Zirconia

L. C. DAMONTE; M.C.CARACOCHE; D.LAMAS

Physica Status Solidi c

Wiley Interscience

Lugar: N.Y.; Año: 2007 vol. 4 p. 3843 - 3846

Zirconia-based ceramic systems have been widely studied due to their excellent mechanical and electrical properties. Three equilibrium polymorphs are known for pure zirconia: monoclinic (up to 1200ºC), tetragonal (up to 2400ºC) and cubic (up to melting point). One of the main objectives in zirconia ceramics research is the stabilization of the tetragonal phase at RT, often achieved by the addition of a trivalent oxide as Y2O3 is. Since a certain amount of oxygen vacancies in the ZrO2 host lattice are created for charge balance, the electrical properties of yttria doped zirconias (YSZ) depend on the defect structure, fact which turns most relevant the characterization and identification of the generated defects. Positron annihilation spectroscopy has proved to be an excellent tool for defects identification. In the present work we present PAS results obtained on the gel-combustion derived 10 mol %Y2O3-stabilized ZrO2 system whose hyperfine characterization by Perturbed Angular Correlations (PAC) has already been reported. The evolution with annealing temperature of the positron annihilation parameters is analyzed in order to determine the existing different defect structures and correlate them with the phase transformations observed by PAC. Preliminary PALS results indicate that positron annihilation occurs mainly in vacancy like defects. The results were compared with those obtained for single crystalline and densified YSZ of different concentrations and also with compact samples of pure oxides.