Simultaneous Measurement of the Electronic and Ionic Conductivity of a Solid Electrolyte
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SIMULTANEOUS MEASUREMENT OF THE ELECTRONIC AND IONIC CONDUCTIVITY OF A SOLID ELECTROLYTE I. RIESS AND R. SAFADI Physics Department, Technion IIT, Haifa 32000, Israel ABSTRACT We describe a method for a simultaneous measurement of the total and electronic conductivities of solid electrolytes (SE). The total conductivity is determined by a four probe method and the electronic (electron/hole) conductivity is determined simultaneously by a two probe method, for samples having the van-der-Pauw configuration. INTRODUCTION When applying reversible electrodes to mixed-ionicelectronic-conductors (MIEC) the interaction of the electrode material with the MIEC may alter the local chemical potential of the atoms corresponding to the mobile ions and therefore affect the I-V relations. When performing four probes conductivity measurements on a MIEC the very application of the two additional probes may thus cause changes in the I-V relations (1]. Four probe measurements are used to be able to exclude the voltage drop on the current electrodes from the voltage measurement. It is normally assumed that the voltage drop on the two additional voltage probes is negligible when a high impedance voltameter is used and the current through these probes almost vanishes. However when measuring on a MIEC the high impendance of the voltameter assures only that the total current through the voltage probes vanishes. The partial currents of the ions, Ii, and of the electrons and holes, Iell need not vanish. If this is the case the reading of the voltmeter are affected by the contact resistance of the voltage probes [1]. The analysis of the four probe conductivity measurement on a MIEC is feasible for the van-der-Pauw[2] configuration as has been shown by Riess and Tannhauser[1]. A one dimensional configuration can be considered only under one of the following three limiting cases: a) All electrodes are ideally reversible and have equal composition. b) At least three of the four electrodes are blocking to ions and the current is purely electronic (electron/hole). c) At least three of the four electrodes, are blocking to electrons and holes and the current is purely ionic.
Mat. Res. Soc. Symp. Proc. Vol. 210. 01991 Materials Research Society
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Addressing the more general cases which do not correspond to these three limits, Riess and Tannhauser were able to calculate the I-V relations on a MIEC having the van-der-Pauw configuration assuming that all chemical gradients are kept small i.e. g
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