Proton conduction related electrical dipole and space charge polarization in hydroxyapatite J. Appl. Phys. 112, 074901 (2012) Phase-field modeling of stress generation in electrode particles of lithium ion batteries Appl. Phys. Lett. 101, 133902 (2012) Simultaneous enhancement of electronic and Li+ ion conductivity in LiFePO4 Appl. Phys. Lett. 101, 033901 (2012) Sodium ionic conduction in complex hydrides with [BH4]− and [NH2]− anions Appl. Phys. Lett. 100, 203904 (2012) Defect chemistry of Ti-doped antiferroelectric Bi0.85Nd0.15FeO3The diffusion of oxygen in ultrafine grained, undoped monoclinic ZrO 2 was studied using 18 O as tracer and secondary ion mass spectroscopy profiling. Samples with a relative mass density of 97%-99% and average crystallite sizes of 80 or 300 nm were prepared from Zr by sputtering, inert-gas-condensation, oxidation, in situ consolidation of nanocrystalline (n-)ZrO 2 powder and subsequent pressureless sintering at 950 or 1050°C in vacuum. Volume and interface diffusivities were directly determined from the 18 O diffusion profiles in n-ZrO 2 in the type B and type A regime of interface diffusion. The diffusion of 18 O in interfaces in undoped n-ZrO 2 is 10 3 -10 4 times faster than in the bulk of the crystallites throughout the temperature range of 450 to 950°C studied. These diffusivities are independent of the crystallite size in the range of 70-300 nm. The activation energies Q V ϭ2.29 eV and Q B ϭ1.95 eV for the volume (Q V ) and interface diffusion (Q B ) are considerably higher than the diffusion activation energies found in the fast ion conductors Ca-or Y-stabilized ZrO 2 . Based on the present data on oxygen diffusion in ZrO 2 , the cation and anion diffusivities of other binary oxides are discussed.

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First measurements of oxygen grain boundary diffusion coefficients in nanocrystalline yttria-doped ZrO2 (n-ZrO2⅐6.9 mol % Y2O3) are presented. The 18 O diffusion profiles measured by secondary ion mass spectroscopy are much deeper in the nanocrystalline specimens than in single crystals. An oxygen diffusivity, D B, in the grain boundaries can be deduced, which is Ϸ3 orders of magnitude higher than in single crystals. From the present data the temperature variation of the oxygen grain boundary diffusivity, D B ‫؍‬ 2.0 ؋ 10 ؊5 exp (؊0.91 eV͞kBT) m 2 ͞s, and the oxygen surface exchange coefficient, k ‫؍‬ 1.4 ؋ 10 ؊2 exp (؊1.13 eV͞kBT) m͞s, are derived. Y ttria stabilized zirconia (ZrO 2 ⅐Y 2 O 3 ) is widely used as an electrolyte material in solid oxide fuel cells or oxygen sensors. The technological importance of the material arises from its extraordinary oxygen transport properties, which are attributed to an oxygen vacancy mechanism. The replacement of quadrivalent Zr by trivalent Y gives rise to a high concentration of structural oxygen vacancies for charge compensation and stabilizes the cubic phase (1). The structural vacancies dramatically increase the mobility of oxygen ions, and the highest ionic conductivities were reported for Y 2 O 3 concentrations of 7-10 mol % (2).There is a broad interest in reducing the high operating temperatures of solid oxide fuel cells, typically 900-1,000°C, and resulting degradation effects by increasing the oxygen ion conductivity of the electrolyte. In undoped monoclinic nanocrystalline ZrO 2 it was found that the diffusion of oxygen in interfaces is 10 3 to 10 4 times faster than in the bulk of the crystallites (3). The question arises as to whether the high oxygen diffusivities of ZrO 2 ⅐Y 2 O 3 upon doping can be further enhanced by the introduction of a large number of crystallite interfaces. A reason for an enhanced oxygen diffusion could be a loosely packed grain boundary structure, which is well established for pure metals (4), or easy formation of vacancy-type free volumes within the grain boundaries (5). On the other hand, there are reports that oxygen transport across grain boundaries could be impeded by a blocking effect due to space charge layers in the grain boundary region (6) or silica-containing grain boundary phases (7). In the present study, we present direct measurements of the grain boundary diffusion coefficients in nanocrystalline ZrO 2 ⅐Y 2 O 3 , which are accomplished by using 18 O as a tracer and secondary ion mass spectroscopy for depth profiling.Fully dense nanocrystalline ZrO 2 ⅐Y 2 O 3 bulk specimens were synthesized by dc sputtering of a ZrY metal target and crystallite condensation in an argon atmosphere at 240 Pa. Subsequent oxidation by slow exposure to an oxygen atmosphere (2,000 Pa) and in situ uniaxial compaction at high pressures (2 GPa) yielded disk-shaped specimens 5 mm in diameter with a relative mass density ͞ 0 Ϸ89% of the green body and a mean crystallite size Ͻ5 nm. From the sputter target with the composition of Zr 84 Y 16 , speci...

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