Degree Type

Dissertation

Date of Award

1992

Degree Name

Doctor of Philosophy

Department

Chemical and Biological Engineering

First Advisor

Glenn L. Schrader

Abstract

A new sol-gel process was developed to produce thin films of Ba[subscript]2Ti[subscript]9O[subscript]20 and BaTi[subscript]5O[subscript]11, and the phenomena of crystallization and phase transition processes of these sol-gel derived thin films during isothermal annealing was studied by the experimental techniques of in situ laser Raman spectroscopy and transmission electron microscopy;Precursor solutions of Ba[subscript]2Ti[subscript]9O[subscript]20 and BaTi[subscript]5O[subscript]11 were produced by first hydrolizing titanium alkoxide and then mixing the resulting titania sol with a barium alkoxide-methanol solution. By using X-ray diffraction and laser Raman spectroscopy, it was shown that BaTi[subscript]5O[subscript]11 was formed from the xerogels of the 1:5 precursor after being sintered at temperatures >700°C and that Ba[subscript]2Ti[subscript]9O[subscript]20 was formed from the xerogels of the 2:9 precursor after prolonged heating at 1200°C. Thin films of Ba[subscript]2Ti[subscript]9O[subscript]20 and BaTi[subscript]5O[subscript]11 were prepared by first spin-coating the precursor solutions with appropriate Ti/Ba ratios onto the substrates and then annealing the resulting films under different conditions to produce the desired phases. By X-ray diffraction, laser Raman spectroscopy, energy dispersive spectrometry, and transmission electron microscopy, it was shown that polycrystalline BaTi[subscript]5O[subscript]11 thin films with random orientation were produced after the amorphous precursor films were annealed above 700°C and that polycrystalline Ba[subscript]2Ti[subscript]9O[subscript]20 thin films with preferred orientation in the (00L) direction were produced on fused silica plates with a platinum overlayer after prolonged heating at 1100°C;The experimental results from the study of the phase transition process showed that by depositing thin films of the precursors on silicon wafers or fused silica plates presputtered with platinum, qualitative in situ Raman studies of the phase transformation process of the thin films of BaTi[subscript]5O[subscript]11 during isothermal annealing could be performed. However, due to the change of the refractive index of the film and the incident angle of the laser probe, the spectral intensity data could not be directly used in the quantitative Avrami analysis.

DOI

https://doi.org/10.31274/rtd-180813-12573

Publisher

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

Copyright Owner

Hsin-Chun Lu

Language

en

Proquest ID

AAI9302009

File Format

application/pdf

File Size

136 pages

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