Author

Tae Il Oh

Date

September 1985

Document Type

Dissertation

Degree Name

Ph.D.

Department

Dept. of Materials Science

Institution

Oregon Graduate Center

Abstract

Stoichiometric TiO2, rutile is an insulator at room temperature, while reduced nonstoichiometric rutile is semiconductive. The electrical properties of nonstoichiometric rutile depend on its defect structure. Reduced rutile is characterized as two groups; a homologous series of phases of Ti[subscript n]O[subscript 2n-1] and nonstoichiometric TiO[subscript 2-x]. In the homologous series of phases, defective crystallographic shear planes (CS planes) are so regular in the rutile structure that a superlattice structure is generated. Before the homologous phases are produced, the state of the reduced crystal is that of the point defect or irregular extended defect state which is expressed as TiO[subscript 2-x](x << 1). The electrical conductivity measurements of undoped and doped rutile at thermodynamic equilibrium with controlled oxygen activities have been conducted and interpreted in terms of corresponding defects within TiO[subscript 2-x]. In very low oxygen activity, an anomalous dependence of conductivity is observed. The conventional point defect model cannot explain this behavior. A new reaction model is derived to interpret the observed results and microstructure analysis under T.E.M. supports the modified model for its application to the phenomenological results at very low oxygen activities.

Identifier

doi:10.6083/M4VX0DFP

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