Ionic conductivity of Zr1−xIn2xO2−x |
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Authors: | DK Hohnke |
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Institution: | Engineering and Research Staff, Research, Ford Motor Company, Dearborn, MI 48121, U.S.A. |
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Abstract: | As x in Zr(In)O2?x is increased from 0.08 to 0.16 (9–19 mole per cent In2O3) the activation energy E(x) for ionic conduction increases from 1.05 to 1.51 eV; the concuctivity decreases from 2 × 10?5 to 3 × 10?6Ω?1cm?1at 400°C, is composition-independent at about 580°C, and increases from 1 × 10?2 to 4 × 10?2Ω?1cm?1 at 800°C. The pre-exponential term of the Boltzmann-type conductivity equation depends exponentially on E(x), a much stronger dependence on x than theoretically expected with a model for ionic conductivity that includes nearest-neighbor defect interactions. Analysis of reported conductivity data for Zr(M)O2?x (M = Sc, Y, Ca and rare earth metals) and other doped oxide electrolytes with fluorite-type structure reveals that the same relationship is observed with these materials when x γ0.08. It is shown that ionic conduction in these oxides is consistent with nearest neighbor vacancy-cation defect interaction forx < 0.08 but that an additional complex interaction with composition-dependent free energy ΔG(x) occurs when xγ 0.08.The lattice constant of Zr(In)O2?x with the cubic fluorite-type structure is independent of composition, 5.114 ± 0.002 Å, in agreement with ionic size considerations. |
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