Ac hopping admittance in spinel manganate negative temperature coefficient thermistor electroceramics

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 φ′ vs ω and (φ′ / φdc) 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 (φ+), an unusually low Jonscher exponent of frequency ∼0.007 was obtained and the GB relaxation displayed close to ideal behavior. © 2008 American Institute of Physics.