dc.contributor.author	Gonzalez, Reinaldo J.	en
dc.contributor.committeechair	Zallen, Richard H.	en
dc.contributor.committeemember	Davis, Richey M.	en
dc.contributor.committeemember	Heflin, James R.	en
dc.contributor.committeemember	Indebetouw, Guy J.	en
dc.contributor.committeemember	Ritter, Alfred L.	en
dc.contributor.department	Physics	en
dc.date.accessioned	2014-03-14T20:22:12Z	en
dc.date.adate	1998-07-13	en
dc.date.available	2014-03-14T20:22:12Z	en
dc.date.issued	1998-07-13	en
dc.date.rdate	1998-07-13	en
dc.date.sdate	1998-07-13	en
dc.description.abstract	Sol-gel titania particles were investigated, primarily by optical techniques, by systematically varying synthesis, sample handling, and annealing variables. The material phases investigated were amorphous titania, anatase TiO2, and rutile TiO2. Annealing-induced phase transformations from amorphous TiO2 to anatase to rutile were studied by Raman scattering, infrared reflectivity, infrared absorption, x-ray diffraction, and electron energy-loss spectroscopy (EELS). Detailed experiments were carried out on the effects of annealing on the Raman and infrared spectra of anatase nanocrystals. The frequencies of the zone-center transverse optical (TO) and longitudinal-optical (LO) phonons of anatase were determined and were used in analyzing the results obtained on composites consisting of annealed solgel particles. The TO and LO frequencies of anatase were obtained from polarization-dependent far-infrared reflectivity measurements on single crystals. These results, which determined the dielectric functions of anatase, were used to explain infrared (IR) reflectivity spectra of titania nanoparticles pressed into pellets, as well as the grazing-incidence IR reflectivity observed for titania thin films. Because of the polycrystalline character of the titania nanoparticles, the surface roughness of the pressed pellets, and the island-structure character of the thin films, effective-medium theories (appropriate for composites) were used, along with the anatase dielectric functions, to interpret the experimental results. The titania nanoparticles were prepared by the hydrolysis/condensation of Ti(OC2H5)4. A polymeric steric stabilizer was used in the sol-gel synthesis in order to prevent continued agglomeration during the condensation process. This yielded particles with a relatively narrow size distribution. The amount of water used in the reaction determines the final particle size. Particles as small as 80 nm and as large as 300 nm were used throughout this work. From the colloidal suspension, loose powders, pressed pellets, and thin films were formed. These samples were subjected to different annealing processes at temperatures ranging from room temperature up to 1000 C. Two different annealing atmospheres were used: air (oxygen-containing) and argon (no oxygen). The amorphous to anatase transformation was followed by in-situ IR transmission measurements carried out during annealing. The particles as prepared are amorphous and the anatase phase could be detected, using this sensitive IR technique, at temperatures as low as 150 C. This phase transition was shown to be particle size dependent. It was also shown that introducing the stabilizer by means of the alkoxide flask instead of the water flask (during the sol-gel synthesis) decreases the anatase to rutile transformation temperature. Loose powders were found to transform more readily than dense pellets, while island-structure films were found to be the hardest to transform. Even at 1000 C, most of these films did not transform to rutile. X-ray diffraction experiments were used to determine nanocrystal sizes in anatase samples obtained by air and argon anneals at temperatures from 300 to 800 C. A correlation was found between Raman band shape (peak position and linewidth) and crystallite size, but this correlation was different for air anneals and for argon anneals. These experiments called for an interpretation based on a stoichiometric effect rather than a finite size effect. Based on this interpretation, the as-prepared particles are slightly oxygen-deficient, with a stoichiometry corresponding to TiO1.98. In the electron energy-loss experiments, a special data-analysis technique was used to extract the EELS spectrum of the titania nanoparticles from the observed substrate-plus-particles signal. This technique successfully resolved the titania absorption-edge peak. Which was found to be momentum independent. For low electron momentum, the results were consistent with the reported optical absorption edge.	en
dc.description.degree	Ph. D.	en
dc.format.extent	xvi, 213 leaves	en
dc.format.mimetype	application/pdf	en
dc.identifier.other	etd-55691079662221	en
dc.identifier.sourceurl	http://scholar.lib.vt.edu/theses/available/etd-55691079662221/	en
dc.identifier.uri	http://hdl.handle.net/10919/30605	en
dc.language.iso	en	en
dc.publisher	Virginia Tech	en
dc.relation.haspart	fig31.jpg	en
dc.relation.haspart	fig32.jpg	en
dc.relation.haspart	fig33.jpg	en
dc.relation.haspart	fig34.jpg	en
dc.relation.haspart	fig35.jpg	en
dc.relation.haspart	fig36.jpg	en
dc.relation.haspart	fig51.jpg	en
dc.relation.haspart	fig61.jpg	en
dc.relation.haspart	fig68.jpg	en
dc.relation.haspart	etd.pdf	en
dc.relation.isformatof	OCLC# 38844941	en
dc.rights	In Copyright	en
dc.rights.uri	http://rightsstatements.org/vocab/InC/1.0/	en
dc.subject	raman	en
dc.subject	infrared	en
dc.subject	nanocrystals	en
dc.subject	phase transitions	en
dc.subject	titania	en
dc.subject	anatase	en
dc.subject.lcc	LD5655.V856 1996.G655	en
dc.title	Raman, Infrared, X-ray, and EELS Studies of Nanophase Titania	en
dc.type	Dissertation	en
dc.type.dcmitype	Text	en
thesis.degree.discipline	Physics	en
thesis.degree.grantor	Virginia Polytechnic Institute and State University	en
thesis.degree.level	doctoral	en
thesis.degree.name	Ph. D.	en

Raman, Infrared, X-ray, and EELS Studies of Nanophase Titania

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