Degree Type

Dissertation

Date of Award

1986

Degree Name

Doctor of Philosophy

Department

Materials Science and Engineering

Abstract

Electrical switching of some polycrystalline ZnO based ceramics was investigated. The electrical characteristics of multicomponent, two-phase, and single-phase materials were related to the microstructures and defect structures of those materials;Subsequent to the study of the multiphase microstructure of multicomponent switching materials, a simplified two-phase threshold switching material was produced consisting of Co-doped ZnO and Zn-doped PrCoO(,3) phases. The roles of individual grains and interphase boundaries in the switching behavior of the two-phase threshold switching material were identified using microelectrodes deposited photolithographically on a thin section of the material. Pristine Co-doped ZnO grains showed high 'off' state resistance and a high 'threshold' voltage drop for the initial voltage sweep and were permanently conductive for subsequent sweeps. Zn-doped PrCoO(,3) grains exhibited stable and reproducible threshold switching behavior. Through the study of the electrical characteristics of single-phase polycrystalline undoped and Co-doped ZnO materials and undoped and Zn-doped PrCoO(,3) materials, the microelectrode observations of the switching behavior of the two-phase material were confirmed. Undoped ZnO showed n-type conductivity with resistivity of around 1 (OMEGA)-cm. Doping ZnO with Co increased the resistivity. It was established through a series of studies that the resistivity increase in ZnO accompanying doping with Co was not due to blocking contacts. A model was proposed for this resistivity increase. Undoped and Zn-doped PrCoO(,3) showed p-type conductivity with a resistivity of around 100 (OMEGA)-cm. Doping PrCoO(,3) with Zn decreased the resistivity. A blocking contact was observed between PrCoO(,3) and electrode metals having low work functions;The Hunter model for switching behavior of ZnO-based materials was tested on the basis of the observed microstructure in the two-phase material, and was found not to be appropriate. A microscopic model of the switching behavior of the two-phase materials was proposed.

DOI

https://doi.org/10.31274/rtd-180813-5789

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Kwangsoo No

Language

en

Proquest ID

AAI8627137

File Format

application/pdf

File Size

205 pages

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