Grain and Grain-Boundary Electric Resistance Characterization via Impedance Spectroscopy

Reference	Presenter	Authors (Institution)	Abstract
08-097	Marcos Augusto Lima Nobre	Nobre, M.A.(Faculdade de Ciências e Tecnologia); Praxedes, F.R.(Faculdade de Ciências e Tecnologia); Bellucci, F.S.(Ministério da Ciência, Tecnologia e Inovação); Lanfredi, S.(Faculdade de Ciências e Tecnologia);	Electrical properties of the Fe doped KSr2Nb5O15 with KSr2(FeNb4)O15-delta stoichiometry were investigated by impedance spectroscopy. Measurements were carried out in the frequency range from 5 Hz to 13 MHz and from 298 up to 973 K. Analysis is focused on the grain and grain-boundary phenomenon. The grain boundary properties are detected at temperature higher than 668 K. Both grain and grain boundary resistivity decrease as a function of temperature similar to materials exhibiting a negative temperature coefficient of resistance. In the temperature range  at 668 K, the classical  beta parameters of a thermistor is investigated. The beta  parameter of grain-boundary is derived being equal to 1.03 x 10e4 K, while the beta one of grain is equal to 0.54 x 10e4 K, in the temperature range from 298 K to 963 K. Grain boundary phenomena contribution to the Thermistor properties is discussed and connected to the d.c. electric conductivity phenomenon.
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