Evaluation of Segregation in Polycrystalline 10 mol% Yttria Doped Zirconia (10YSZ)
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Evaluation of Segregation in Polycrystalline 10 mol% Yttria Doped Zirconia (10YSZ) Muhammad Asri Idris1,3, Janusz Nowotny2, Sean S. Li1 1 School of Materials Science and Engineering, The University of New South Wales, Sydney, New South Wales, AUSTRALIA 2 Solar Energy Technologies, School of Natural Sciences, University of Western Sydney, Penrith South DC, New South Wales, AUSTRALIA 3 School of Materials Science and Engineering, University Malaysia Perlis, Kubang Gajah, Perlis, MALAYSIA ABSTRACT The present work reports surface segregation in polycrystalline yttria-stabilised zirconia (cubic) including 10 mol% Y2O3 (10YSZ). The 10YSZ specimen was annealed in the range 1073 K - 1673 K in the gas phase of controlled oxygen activity. The segregation-induced intensity profiles of 89Y, 40Ca, 28Si, 27Al, 133Cs, 197Au and 90Zr was measured using secondary ion mass spectrometry (SIMS). The data obtained show that (i) annealing of 10YSZ results in the formation of segregation-induced concentration gradients of 89Y, 40Ca, 28Si, 27Al and (ii) segregation-induced profiles depend on oxygen activity. INTRODUCTION There has been an accumulation of data indicating that the performance of yttriastabilised zirconia (YSZ) in electrochemical devices, is strongly influenced by interfaces rather than the bulk phase[1-2]. Awareness is growing that properties of interfaces, such as the local chemical composition, differ from those of the bulk phase as a result of segregation. The studies on segregation in solids resulted in collection of a considerable amount of data for metal and alloys. These data led to derivation of theoretical models, which are valid mainly for metallic solids [3-5]. So far, however, little is known about the effect of segregation in compounds, including metal oxides. This limitation results from the difficulties in quantitative assessment of surface composition of oxides. The first comprehensive data on segregation of yttrium in YSZ were reported by Burggraaf et al. [6] and Winnubst et al. [1]. Their study indicate that the segregation-induced surface composition of YSZ reaches 19-23 mol% regardless of bulk composition, which varies between 2 and 21 mol%. These data indicate that the surface layer of YSZ is best stabilized at the surface content of approximately 20 mol% of Y2O3. The aim of the present work is to investigate the effect of segregation on surface properties of 10YSZ. The segregation-induced surface enrichment for the 10YSZ specimens annealed in the ranges of temperature, 1073 K – 1673 K, and oxygen activity, 10-10 Pa < p(O2) < 75 kPa, was determined using the secondary ions mass spectrometry (SIMS). This technique allows the determination of depth profiles of selected lattice elements.
EXPERIMENTAL Polycrystalline specimens of 10 mol% yttria stabilised zirconia (10YSZ) powder was obtained from Tosoh Corp., Tsukuba, Japan. The zirconia powder was isostatically pressed at 200 MPa into discs of 1 mm thickness and 8 mm in diameter. The discs were then sintered at 1673 K for 2 h in air, grinded and polished
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