Abstract
Any theory of electrical conduction in TFRs encounters mainly two problems: (i) explanation of the dependence of R□on properties of conducting component (volume fraction, grain size, resistivity), (ii) explanation of the temperature dependence of R□taking into account (i). In order to achieve this one has to fit some microscopic parameters to experimental R□-and TCR-values, and to check if they are reasonable or not. The aim of the following discussion is to show, that such a fitting by means of experimental TCR-values is not correct. This is due to the fact that TCR-behaviour, as is well known, is determined also by the dependence of resistivity on strain. But any theoretical model neglects strains, also those who are induced by thermal strains. By means of published experiments concerning the strain dependence of resistance, the magnitude is estimated by which the TCR-values have to be corrected for the described fit.
Highlights
One of the most important properties, that any theory of TFRs has to explain, is their very low TCR at ambient temperatures
A lot of experimental results and their theoretical analysis led to the conclusion, that tunnelling through glassy interlayers determines the resistivity of TFRs. 1’2 It is well known, that TFRs exhibit a large piezo-resistive effect.[3]
The aim of this paper is to show, that because of the piezo-resistive effect, the measured TCR-values have to be corrected by a term, determined by strain dependence of the resistivity, if they are to be compared with theoretical models or are to be used to fit any parameter in such models
Summary
One of the most important properties, that any theory of TFRs has to explain, is their very low TCR at ambient temperatures. A lot of experimental results and their theoretical analysis led to the conclusion, that tunnelling (modified, because of trap-activation and the small size of metallic-like grains) through glassy interlayers determines the resistivity of TFRs. 1’2 It is well known, that TFRs exhibit a large piezo-resistive effect.[3] The aim of this paper is to show, that because of the piezo-resistive effect, the measured TCR-values have to be corrected by a term, determined by strain dependence of the resistivity, if they are to be compared with theoretical models or are to be used to fit any parameter in such models. This is necessary, because in any theoretical model thermal expansion of TFR is neglected
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