Date of Award

Summer 1996

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Electrical and Computer Engineering

First Advisor

Blumenthal R. N.

Second Advisor

Brower, Willaim E. Jr.

Abstract

The electrical conductivity of sintered specimen of 10 mole% Gd203-doped Ce02 was measured over the range 800°C - 1000°C and from 1 to 10-24 atm of oxygen. This measurement was conducted to determine the impurity generated and nonstoichiometric defects and their transport properties in the gadoliniadoped ceria. The electrical conductivity of Gd203-doped Ce02 exhibited mixed conduction. Predominantly ionic conductivity was observed at low temperatures(700°C-800°C) and high oxygen partial partial pressures(1-10-7 atm). When compared to 10 mole% CaO-doped Ce02, 10 mole% Gd203 showed a lower ionic conductivity but the almost same electronic conductivity behavior. Conversly, high temperatures and lower oxygen partial pressures were dominated by electronic conductivity. In the temperature(900-1000°C) and oxygen partial pressure region(l-10-15 atm) investigated, the ionic and electronic mobilities were obtained in terms of a defect model involving impurity defects (doubly ionized oxygen vacancies "formula" and nonstoichiometric defects(localized electrons "formula". The values of μe and μv-at l000°C were 0.019 and 4.72x 10-5(cm2/V xs), while the values at 900°C were 0.017 and 1.21 x10-5(cm2/Vxs). The dc electrical conductivity of the specimen was measured in the temperature range of 600-1000°C and from 1-10-4 atm of oxygen partial pressure. Respective activation energies were determined by applying the law of mass action. Using the form "formula", the activation energies were 0.73eV. The ionic transference number t, obtained from isothermal plots as a function of oxygen partial pressure was similar to previous results of Y203-doped Ce02 and the calculated value in the high P02 region (1-10-6atm) was above 0.93.

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