ELECTRONIC AND IONIC CONDUCTION IN IRON-DOPED BETA"-ALUMINA
Abstract
The electrical properties of iron doped (beta)"-alumina were studied as a function of temperature by using complex plane analysis to determine the electronic and ionic conductivity. While the ionic conductivity at 300(DEGREES)C was high ((DBLTURN)0.1 ((OMEGA)(.)cm)('-1)), the electronic conductivity was small relative to the ionic conductivity for the compositions studied--the largest transference number was (DBLTURN)0.04. Two anomalies were found in the electrical conductivities, one at 245(DEGREES)C and the other at 891(DEGREES)C. The findings agreed well with those obtained from differential thermal analysis (DTA) studies, although an additional transformation was seen using DTA. At 550(DEGREES)C an exothermic transformation was discovered. Magnetization vs. magnetic field studies helped identify the transformation at 245(DEGREES)C as a ferrimagnetic or ferromagnetic to paramagnetic transition. Magnetic susceptibilities were determined for those samples which behaved paramagnetically. Iron doped beta"-alumina rapidly quenched from a given oxygen partial pressure and temperature was examined for new phases with an x-ray diffractometer. Chemical analysis was used to determine the ferrous iron content as a function of oxygen partial pressure and temperature. A theoretical development of the relationship between polycrystalline and single crystal conductivity was carried out. For a random orientation of grains the single crystal conductivity was calculated to be twice the intragranular conductivity.
Degree
Ph.D.
Subject Area
Materials science
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