Structure and Chemistry of Yttria‐Stabilized Cubic‐Zirconia Symmetric Tilt Grain Boundaries

Dickey, Elizabeth C.; Fan, Xudong; Pennycook, Stephen J.

doi:10.1111/j.1151-2916.2001.tb00842.x

Cited by 99 publications

(84 citation statements)

References 42 publications

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“…Specific information on the atomic structure of ZrO 2 ⅐10 mol % Y 2 O 3 grain boundaries has recently been obtained by analytical high-resolution transmission electron microscopy (23,24). Making use of Z-contrast imaging and electron energy-loss spectroscopy (EELS) on a symmetric 24°[001] tilt boundary an increase of the yttrium concentration in the grain boundary core by about a factor of 2 has been found, as anticipated by early auger electron spectroscopy͞x-ray photoelectron spectroscopy (25) and energy dispersive x-ray spectroscopy (22) studies.…”

Section: Figmentioning

confidence: 99%

Enhanced oxygen diffusivity in interfaces of nanocrystalline ZrO ₂ ⋅Y ₂ O ₃

Knöner

Reimann

Röwer

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

119

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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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Section: Figmentioning

confidence: 99%

Enhanced oxygen diffusivity in interfaces of nanocrystalline ZrO ₂ ⋅Y ₂ O ₃

Knöner

Reimann

Röwer

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

119

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“…En el caso particular del YSZ hay evidencias experimentales de que existe una segregación de vacantes de oxígeno hacia el núcleo de la frontera de grano que genera un exceso de carga positiva. Este exceso de carga positiva se compensa en la región adyacente, zona de carga espacial, con un empobrecimiento de vacantes (25,26). Las zonas de carga espacial se comportan como barreras Schottky y el transporte iónico se describe en base a este modelo (11,27).…”

Section: Resultados Y Discusiónunclassified

Caracterización eléctrica de fronteras de grano en conductores iónicos mediante medidas de espectroscopia de impedancias en un bicristal

Frechero¹,

Rocci²,

Schmidt³

et al. 2012

Bol. Soc. Esp. Ceram. Vidr.

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En este trabajo se presentan resultados de medidas de espectroscopia de impedancias realizadas en un bicristal del conductor iónico zirconia estabilizada con itria (YSZ). Utilizando electrodos de tamaño micrométrico se ha podido medir el transporte iónico a través, perpendicularmente, de una única frontera de grano, caracterizando eléctricamente las propiedades de dicha frontera. De este modo se han obtenido los parámetros microscópicos que determinan la distribución de carga en la frontera y por lo tanto el transporte iónico a través de ella, como son la barrera de potencial en la frontera DF = 0.35±0.01 V a 275 ºC, y el espesor de la zona de carga espacial l * = 5±1 Å. Estos valores son significativamente diferentes a los obtenidos anteriormente en muestras cerámicas policristalinas del mismo material, y muestran mejor acuerdo con los valores que predice el modelo de Mott-Schottky para la distribución de carga y el transporte iónico a través de la frontera de grano. Palabras clave: Conductividad. Bordes de grano. Conductores iónicos. Electric characterization of grain boundaries in ionic conductors by impedance spectroscopy measurements in a bicrystalHere we show impedance spectroscopy measurements on a bicrystal of the ionically conducting yttria stabilized zirconia (YSZ). By using micrometer sized electrodes it is possible to measure ionic transport perpendicular to a single grain boundary, and characterize its electrical properties. We are thus able to obtain the microscopic parameters that determine the charge distribution at the grain boundary and the ionic transport through it, as the potential energy barrier DF = 0.35±0.01 V at 275 ºC, and the space charge layer thickness l * = 5±1 Å. These values are significantly different from those previously obtained in polycrystalline ceramic samples of the same material, and show much better agreement with the values predicted by the Mott-Schottky model for the charge distribution and ionic transport through the grain boundary. Kedywords: Conductivity. Grain boundaries. Ionic conductors. INTRODUCCIÓNCuando se reduce alguna de las dimensiones de un material hasta el rango de los nanómetros pueden aparecer comportamientos en sus propiedades físicas que se desvían del comportamiento que presenta el mismo material cuando sus dimensiones son mayores, típicamente por encima de la micra. Esto es debido a que las longitudes características que gobiernan muchos fenómenos físicos son típicamente del orden de unos pocos nanómetros. En los últimos años, debido a la posibilidad de acceder con mayor facilidad a la escala nanométrica, existe un elevado interés por estudiar este tipo de efectos de tamaño sobre las propiedades físicas de los materiales. En particular, en el área de los materiales conductores iónicos, la investigación en este tipo de efectos ha dado lugar a un nuevo campo científico que se ha dado en denominar "nanoiónicos" (1-4). Al disminuir el tamaño de grano en muestras nanocristalinas, o el espesor en películas ultradelgadas, aumenta drásticamente el número y...

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“…There are already experimental and computational studies of this GB reported in the literature [10,11]. Two structural modications of this GB were already examined with positrons in [5] and we study the lower GB energy variant here.…”

Section: Computational Proceduresmentioning

confidence: 99%

Comparison of Grain Boundary Structure in Metals and Semiconductors as Probed by Positrons

Kuriplach

2014

Acta Phys. Pol. A

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Vacancy behavior and positron trapping at selected grain boundaries in iron, nickel, and zirconia are investigated theoretically. It is found that the grain boundary vacancy loses its free volume in metals at moderate temperatures whereas it is kept up to very high temperatures in zirconia. The consequences of these ndings for positron annihilation studies of nanocrystalline materials are discussed.

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Structure and Chemistry of Yttria‐Stabilized Cubic‐Zirconia Symmetric Tilt Grain Boundaries

Cited by 99 publications

References 42 publications

Enhanced oxygen diffusivity in interfaces of nanocrystalline ZrO ₂ ⋅Y ₂ O ₃

Enhanced oxygen diffusivity in interfaces of nanocrystalline ZrO ₂ ⋅Y ₂ O ₃

Caracterización eléctrica de fronteras de grano en conductores iónicos mediante medidas de espectroscopia de impedancias en un bicristal

Comparison of Grain Boundary Structure in Metals and Semiconductors as Probed by Positrons

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Structure and Chemistry of Yttria‐Stabilized Cubic‐Zirconia Symmetric Tilt Grain Boundaries

Cited by 99 publications

References 42 publications

Enhanced oxygen diffusivity in interfaces of nanocrystalline ZrO 2 ⋅Y 2 O 3

Enhanced oxygen diffusivity in interfaces of nanocrystalline ZrO 2 ⋅Y 2 O 3

Caracterización eléctrica de fronteras de grano en conductores iónicos mediante medidas de espectroscopia de impedancias en un bicristal

Comparison of Grain Boundary Structure in Metals and Semiconductors as Probed by Positrons

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Enhanced oxygen diffusivity in interfaces of nanocrystalline ZrO ₂ ⋅Y ₂ O ₃

Enhanced oxygen diffusivity in interfaces of nanocrystalline ZrO ₂ ⋅Y ₂ O ₃