Zirconia grain boundary resistance

In view of the trend to reduce the operation temperature of fuel cells and in view of the highly thermally activated (ca. 0.8 eV at 800...1000°C ) conductivity, the electrol3de conductivity becomes an increasing problem. In particular the influence of grain boundaries deserves more attention at lower temperatures. Amongst the factors influencing the grain boundary resistance of zirconia (and ceria loe-io existence of resistive... 

Figure 4.1.34. Arrhenius plots of the grain interior and grain boundary resistivities for two zirconia ceramics (a) Tetragonal zirconia ceramic (Zr02 3 mole % Y2O3) in which the lines have different slopes, as expected from the brick layer model, b) Partially stabilized ceramic (Zr02 6 mole % Y2O3) in which the slopes of the lines are similar, as expected for discrete grain boundary phase. (Courtesy of Silicates Industriels.)...

Grain internal resistance (Ri) of zirconia particle on the real axis as lead wires and solid electrolyte, zirconia grain boundary matrix resistance (R2), and interface resistance (R3) between zirconia Pt electrodes constitute DC component. The sensor element is exposed to the exhaust gas and R3 resistance suffers effect of the atmosphere. Therefore, if resistance component of the mainstream of grain internal resistance is realized, the sensor element resistance to detect in the high-frequency region, relationship between the sensor element temperature and resistance can be realized without effect of the atmosphere. 

Badwal, S. P. S. (1995). Grain boundary resistivity in zirconia-based materials effect of sintering temperatures and impurities. Solid State Ionics 76 67-80. 

The Model of Grain-Boundary Resistivity in Stabilized Zirconia Ceramics... 

The grain boundary and electrode features are associated with Warburg components of 3 x 10 cm s and 1.3 x lO S cm s respectively. The known properties of the zirconia phase do not, however, fit such an interpretation the resistivity, extrapolated from higher temperature is at least lO Qcm. This would suggest... 

Aruna et al. (2009) showed enhanced performance of wear and corrosion characteristics of Ni based composite coatings by embedding with alumina yttria dop>ed cubic zirconia (AZY, (l-x)Al2Q3-8 mol% yttria stabilized xZxCh x = 10 wt%)) particles. The higher Warburg resistance of Ni - AZY and enhanced corrosion resistance was attributed to possible difference in mass transport phenomena in the Ni -AZY composites compared to the pure Ni with increased resistance of Ni grain boundaries in presence of AZY particles and thereby hindered the diffusion of chloride ions (Aruna et al., 2009). 

Fig.2 Schematic complex impedance spectrum of the stabilized zirconia. R, C, and x mean the resistance, capacitance and relaxation time constant, respectively. From the low frequency, subscripts ep , gb , and gi mean the electrode polarization, grain boundary and grain interior, respectively.

Fig.3 (a) Schematic diagram showing the ionic conduction in polycrystalline stabilized zirconia specimen with a resistive grain boxmdary and (b) its simplification by the brick layer model, (d electrode area, / specimen thickness, dgi average grain size, <%4 grain boundary thickness)... 

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