PAS study on the defect structure of Yttria Stabilized Zirconia

L.C. DAMONTE, M.A.TAYLOR, J. DESIMONI, J. RUNCO, C. CARACOCHE

Coimbra, Portugal

Workshop; 8th International Workshop on Positron and Positonium Chemistry; 2005

Y2O3-stabilized ZrO2 (YSZ) is an important functional and structural material. The electrical properties of YSZ depend on its defect structure. When a trivalent oxide as Y2O3 is added as a stabilizer to ZrO2, certain amount of lattice defects, e.g. oxygen vacancies Vo¢«¢« and negatively-charged solutes Y¢¥Zr, are produced in the ZrO2 lattice. Mechanical milling has proved to be an effective processing technique to produce nanocrystalline materials. Under milling, the powders are subjected to severe plastic deformation giving rise to particle and grain refinement, creating, simultaneously, different kinds of defects. In the present work results on the positron annihilation characteristics in the system Y2O3-stabilized ZrO2 prepared by mechanical milling are presented. Stoichiometric amounts of ZrO2 and Y2O3 powders to obtained 8 mol % ytria stabilized zirconia were milled for 70h in an oscillatory ball mill. The powders were then pressed into pellets and heated at 1200¨¬C for increasing times in order to identify the mechanical induced defects. The results were compared with those obtained for single crystalline and densified YSZ and also with compact samples of pure oxides. Preliminary PALS results on milled samples indicate that positron annihilation occurs in vacancies and in large open volume defects like vacancy-clusters and voids. The evolution with annealing temperature of the positron annihilation parameters is analyzed.