FREQUENCY DEPENDENCE OF THE GRAIN-BOUNDARY CONDUCTIVITY IN (Y2O3, CaO)-STABILIZED ZrO2

Five samples of mixed Y 2 O 3/ CaO doped ZrO 2 electrolytes, with the same nominal chemical composition of ( ZrO 2)0.90–( Y 2 O 3)0.04-( CaO )0.06, were sintered at 1600°C for 2, 4, 6, 8 and 10 h, respectively. The frequency dependence of the grain-boundary conductivity of each sample was measured using complex impedance method in the temperature range from 773 to 1073 K and experimental results were analyzed according to a power law, which was frequently referred to as the so-called universal dynamic response (UDR). Results indicated the apparent ac grain-boundary conductivity can be well-described by the power law and some useful information about the grain-boundary effect, such as the activation energy of the grain-boundary conduction and the dissociated energy of the charge carrier in the space charge layer, can be obtained by analyzing the temperature dependence of the power law parameters.

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Grain boundary effects in NTC-PTC composite thermistor materials

Journal of Materials Research ◽

10.1557/jmr.1999.0019 ◽

1999 ◽

Vol 14 (1) ◽

pp. 120-123 ◽

Cited By ~ 10

Author(s):

D. J. Wang ◽

J. Qiu ◽

Y. C. Guo ◽

Z. L. Gui ◽

L. T. Li

Keyword(s):

Energy Level ◽

Grain Boundary ◽

Boundary Effect ◽

Complex Impedance ◽

Negative Temperature ◽

Impedance Analysis ◽

Composite Effect ◽

Complex Impedance Analysis ◽

Temperature Coefficient Of Resistivity ◽

Grain Boundary Effect

Yttrium-doped (Sr0.45Pb0.55)TiO3 ceramics have been studied by complex impedance analysis. As a sort of NTC-PTC composite thermistor, it exhibited a significantly large negative temperature coefficient of resistivity below Tc in addition to the ordinary PTC characteristics above Tc. It is found that the NTC effect in NTC-PTC materials was not originated from the deep energy level of donor (bulk behavior), but from the electrical behavior of the grain boundary. Therefore, the NTC-PTC composite effect was assumed to be a grain boundary effect, and yttrium was a donor at shallow energy level. The NTC-PTC ceramics were grain boundary controlled materials.

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Effect of Reduced Atmosphere Sintering on Blocking Grain Boundaries in Rare-Earth Doped Ceria

Inorganics ◽

10.3390/inorganics9080063 ◽

2021 ◽

Vol 9 (8) ◽

pp. 63

Author(s):

Soumitra Sulekar ◽

Mehrad Mehr ◽

Ji Hyun Kim ◽

Juan Claudio Nino

Keyword(s):

Activation Energy ◽

Rare Earth ◽

Ionic Conductivity ◽

Grain Boundary ◽

Grain Boundaries ◽

Complex Impedance ◽

Doped Ceria ◽

Composite Electrodes ◽

Boundary Conductivity ◽

Rare Earth Doped

Rare-earth doped ceria materials are amongst the top choices for use in electrolytes and composite electrodes in intermediate temperature solid oxide fuel cells. Trivalent acceptor dopants such as gadolinium, which mediate the ionic conductivity in ceria by creating oxygen vacancies, have a tendency to segregate at grain boundaries and triple points. This leads to formation of ionically resistive blocking grain boundaries and necessitates high operating temperatures to overcome this barrier. In an effort to improve the grain boundary conductivity, we studied the effect of a modified sintering cycle, where 10 mol% gadolinia doped ceria was sintered under a reducing atmosphere and subsequently reoxidized. A detailed analysis of the complex impedance, conductivity, and activation energy values was performed. The analysis shows that for samples processed thus, the ionic conductivity improves when compared with conventionally processed samples sintered in air. Equivalent circuit fitting shows that this improvement in conductivity is mainly due to a drop in the grain boundary resistance. Based on comparison of activation energy values for the conventionally processed vs. reduced-reoxidized samples, this drop can be attributed to a diminished blocking effect of defect-associates at the grain boundaries

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