On Proton Conductivity in Porous and Dense Yttria Stabilized Zirconia at Low Temperature (original) (raw)
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physica status solidi (a), 2012
The electrical cross-plane conductivity of 8 mol% yttria stabilized zirconia (YSZ) thin films prepared by different deposition techniques, namely aerosol assisted chemical vapor deposition, wet spray pyrolysis (SP), and pulsed laser deposition (PLD), is correlated with their microstructure. Depending on deposition technique and process conditions, microstructures ranging from amorphous to randomly oriented nanocrystalline or columnar with preferred (111) orientation are obtained. Cross-plane AC impedance measurements of these thin films show that the oxygen ion conductivity of randomly oriented nanocrystalline samples is determined by the grain boundaries, which show significantly lower transport properties than the grain interior. In columnar microstructures, the conductivity is determined by ionic transport through the grains only. The same conduction behavior is found for amorphous and randomly oriented microstructures with grain sizes between 3 nm and 9 nm, indicating that no true size effects occur in 8 mol% YSZ.
Ionic and electronic conductivities of yttria- and scandia-stabilized zirconia
Inorganic Materials, 2014
We report a study and comparative analysis of the medium temperature (850-1000°C) ionic and total conductivities of zirconia stabilized by yttria and scandia based mixed oxides. Zirconia stabilized by combined yttria and scandia based dopants is shown to have low electronic conductivity in a wide range of oxygen activities. Our data suggest the possibility of using the synthesized materials as membranes in inter mediate temperature ceramic fuel cells.
Conductivity measurements of various yttria-stabilized zirconia samples
Journal of Materials Science, 1994
Samples of yttria-stabilized zirconia manufactured by the following fabrication procedures, were obtained from commercial sources: (i) hot isostatic pressing; (ii) tape casting; (iii) vacuum plasma spraying, and (iv) calendering. The ionic conductivities of these samples were measured by (a) impedance spectroscopy; (b) the four-point probe method; (c) the current-interruption technique, and (d) the van der Pauw technique. The tape-cast and hot pressed samples showed good and very reproducible conductivity values. The vacuum plasma sprayed samples showed an anisotropy in their conductivity, with the cross-plane value being several times lower than the in-plane value. A simple model based on the porous microstructure of these samples can explain this observation. Sintering of the plasma sprayed samples minimized the anisotropy and significantly improved their conductivity values. The calendered samples also showed a similar anisotropy in their conductivity data when they were inadequately sintered.
Investigation of protonic conduction in Yb- and Y-doped barium zirconates
Solid State Ionics, 1995
Barium zirconate ceramics doped with Y and Yb, BaM,Zr, _$_ (I (M = Yb, Y), are perovskite single phases and exhibit protonic conduction in moist nitrogen atmospheres at temperatures 500 < T ("C) < 1000. Samples with x = 0.10 have been investigated by ac and dc electrochemical techniques. Conductivities with Yb as dopant were larger, by a factor = 10, than those with Y as dopant. Conductivities for Yb-doped samples (e.g. u,, (750°C) = 2 X 10m4 S cm-') are lower than those reported for analogous cerates. Throughout the experimental temperature range, the apparent conductivity found in dc studies (summing resistances due to the electrolyte and electrode-electrolyte interfacial phenomena) was lower, by a temperature independent factor = 2, than the conductivity determined by ac techniques.
Ionic conductivity of nanocrystalline yttria-stabilized zirconia: Grain boundary and size effects
Physical Review B, 2010
We report on the effect of grain size on the ionic conductivity of yttria-stabilized zirconia samples synthesized by ball milling. Complex impedance measurements, as a function of temperature and frequency are performed on 10 mol % yttria-stabilized zirconia nanocrystalline samples with grain sizes ranging from 900 to 17 nm. Bulk ionic conductivity decreases dramatically for grain sizes below 100 nm, although its activation energy is essentially independent of grain size. The results are interpreted in terms of a space-charge layer resulting from segregation of mobile oxygen vacancies to the grain-boundary core. The thickness of this space-charge layer formed at the grain boundaries is on the order of 1 nm for large micron-sized grains but extends up to 7 nm when decreasing the grain size down to 17 nm. This gives rise to oxygen vacancies depletion over a large volume fraction of the grain and consequently to a significant decrease in oxide-ion conductivity.
Yttrium-doped barium zirconate ceramic powders were synthesized by the oxidant peroxide method in air and under controlled atmosphere of nitrogen inside a glove box. The powders were characterized by thermogravimetry, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. After uniaxial cold isostatic pressing, green pellets were sintered at 1600°C for 4 h. The electrical conductivity behavior was accessed by electrochemical impedance spectroscopy. The results show that specimens synthesized under controlled atmosphere achieved higher electrical conductivity, two orders of magnitude higher than specimens prepared in laboratory air. The enhancement in electrochemical properties and increase in sintering ability is attributed to the less carbonate contamination as a result lower grain boundary density in the samples prepared under controlled atmosphere.
Effect of ion implantation doping on electrical properties of yttria-stabilized zirconia thin films
Solid State Ionics, 1992
The change in conductivity of Fe and Ti implanted if-sputtered layers of yttria-stabilized zirconia (YSZ) was studied as a function of the temperature (400-800 °C) and oxygen partial pressure. In an oxidized state and in the temperature range of 400-600 ° C, the conductivity of the Fe implanted YSZ film ( 15 keV, 8 × 10 '6 at.cm -2) was dominated by the n-type electronic conductivity of a thin Fe203 layer with an estimated thickness of less than 2 nm on top of the YSZ thin film. Due to the incorporation of a part of the implanted Fe atoms in the yttria-stabilized zirconia lattice, the ionic conductivity was somewhat decreased. In a reducing atmosphere this electronic conduction was no longer observed. In an oxidized state, the conductivity of the YSZ film was not influenced by the implantation of Ti ( 15 keV, 8 X 1016 at.cm-2). After reduction in a H2 atmosphere, an increase in the conductivity of the sputtered film with 2-3 orders of magnitude was observed. This has been ascribed to the presence of nonstoichiometric TiO2_x, which is an n-type semiconductor.
Ionic conductivity of e-beam deposited yttrium stabilized zirconia thin films
Lithuanian Journal of Physics, 2007
In the present study yttrium stabilized zirconia (YSZ) thin films were deposited on the Alloy-600 and optical quartz substrates using e-beam deposition technique with controlled deposition parameters: substrate temperature (Ts) and electron gun power (P) influencing the thin film deposition mechanism. The dependence of these parameters on thin film ionic conductivity, structure, and surface morphology was investigated by X-ray diffraction and scanning electron microscopy (SEM). It was found that electron gun power has the influence on the crystallite size, texture, and roughness of YSZ films. Dominating dispersion in the deposited YSZ thin films (substrate temperature T = 250 • C, e-beam gun power P = 0.9 kW) relates to ionic transport in the crystallites in the measured frequency and temperature ranges. The measured values of conductivity and its activation energies are those typical of the polycrystalic ZrO2-8 mol% Y2O3 compound. The conductivity values of crystallites of YSZ thin films and ceramics are similar. Differences are found only in thin films deposited at T = 250 • C and P = 0.66 kW.