Radiation Physics and Chemistry 76 (2007) 248–251 PALS study on the defect structure of yttria-stabilized zirconia L.C. Damonte à , M.A. Taylor, J. Desimoni, J. Runco Departamento de Fı´sica, Facultad de Ciencias Exactas—U.N.L.P. and IFLP—CONICET, C.C. No. 67 1900 La Plata, Argentine Abstract Powders of stabilized ZrO 2 –8 mol% Y 2 O 3 (YSZ) have been obtained by mechanical milling in zirconia vials. The samples were characterized by X-ray diffraction (XRD). Positron annihilation lifetime (PALS) measurements were performed to investigate the lattice defects originated by the incorporation of yttria and those mechanically induced. The XRD results indicate the formation of tetragonal YSZ solid solution. PALS results indicate that positron trapping occurs at different kinds of defects such as vacancy-like defects, grain boundary and associated defects. r 2006 Elsevier Ltd. All rights reserved. 1. Introduction The strategic functional zirconia material has found extensive application in electrochemical devices, such as gas sensors, solid oxide fuel cells and water hydrolysis cells (Wang et al., 2000; Guo and Zhang, 2003). When a trivalent oxide, e.g. Y 2 O 3 , is added to ZrO 2 as stabilizer, lattice defects like oxygen vacancies V O 2+ and negatively charged substitutional solutes Y Zr  are created in the ZrO 2 lattice. The conductivity of stabilized ZrO 2 is determined by the defect structure, including V O 2+ ,Y Zr  and negatively charged or neutral defect associates. The reactions of the defect production can be summarized as follows (Wang and Nowick, 1981): Y 2 O 3 ! 2Y  Zr þ V 2þ O þ 3O O , Y  Zr þ V 2þ O !ðY  Zr V 2þ O Þ þ , ðY  Zr V 2þ O Þ þ þ Y  Zr !ðY  Zr V 2þ O Y  Zr Þ 0 . Mechanical milling has proved to be an effective processing technique to produce nanocrystalline materi- als. Under milling, the powders are subjected to severe plastic deformation giving rise to particle and grain refinement, creating, simultaneously, different kinds of defects (Koch, 1989, Weeber and Bakker, 1988). The positron annihilation lifetime (PALS) technique is based on the measurement of the positron lifetime inside the studied material (Brandt and Dupasquier, 1983; Hautojarvi, 1979). After the positron reaches the thermal equilibrium with the host material, it eventually annihilates an electron leading to the emission of gamma rays, which gives the experimental informa- tion. The annihilation can take place in interstitial regions characterized by an extended Bloch state (free state) or as trapped positrons in a bound state. Different kind of defects (such as monovacancies, larger vacancy clusters, dislocations) can act as trapp- ing centres but only neutral or negatively charged ones can be effective positron traps (Puska and Nieminen, 1994). Preliminary results on positron lifetime parameters in the ZrO 2 –8 mol%Y 2 O 3 stabilized system prepared by mechanical milling are presented. X-ray diffraction (XRD) was employed to identify the phases. The starting powder oxides and the single crystal were also studied. ARTICLE IN PRESS www.elsevier.com/locate/radphyschem 0969-806X/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2006.03.046 à Corresponding author. E-mail address: damonte@fisica.unlp.edu.ar (L.C. Damonte).