ac hopping admittance in spinel manganate negative temperature coefficient thermistor electroceramics
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2008
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American Institute of Physics
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Abstract
In this work, the ac admittance of a thick film nickel manganate spinel negative temperature coefficient thermistor ceramic system containing a glass phase is investigated. The dominating relaxation process is a grain boundary (GB) effect and has been investigated comprehensively. We present double-logarithmic plots of the specific admittance σ' vs ω and (σ'/σ_(dc)) vs ω, and specific impedance z vs −z"/ω and [(ρ_(dc)/z')−1] vs ω, in order to characterize GB charge transport. Using the complex admittance notation (σ*), an unusually low Jonscher exponent of frequency ~0.007 was obtained and the GB relaxation displayed close to ideal behavior.
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© 2008 American Institute of Physics. The authors wish to thank Michael Petty for allowing use of the ac impedance spectroscopy facility. Thanks to Finlay Morrison and Ian Terry for useful discussions concerning impedance spectroscopy data analysis. Thanks to Andreas Roosen and Alfons Stiegelschmitt for the guidance provided in developing thick film samples.