title: Study of paramagnetic defect centers in as-grown and annealed TiO2anatase and rutile nanoparticles by a variable-temperature X-band and high-frequency (236 GHz) EPR.
abstract: Detailed EPR investigations on as-grown and annealed TiO2nanoparticles in the anatase and rutile phases were carried out at X-band (9.6 GHz) at 77, 120-300 K and at 236 GHz at 292 K. The analysis of EPR data for as-grown and annealed anatase and rutile samples revealed the presence of several paramagnetic centers: Ti3+, O-, adsorbed oxygen (O2-) and oxygen vacancies. On the other hand, in as-grown rutile samples, there were observed EPR lines due to adsorbed oxygen (O2-) and the Fe3+ions in both Ti4+substitutional positions, with and without coupling to an oxygen vacancy in the near neighborhood. Anatase nanoparticles were completely converted to rutile phase when annealed at 1000° C, exhibiting EPR spectra similar to those exhibited by the as-grown rutile nanoparticles. The high-frequency (236 GHz) EPR data on anatase and rutile samples, recorded in the region about g = 2.0 exhibit resolved EPR lines, due to O-and O2-ions enabling determination of their g-values with higher precision, as well as observation of hyperfine sextets due to Mn2+and Mn4+ions in anatase.
authors.affiliation: Physics Department, Concordia University, 1455 de Maisonneuve Blvd West, Montreal, QC H3G 1M8, Canada.
authors.forename: S K
authors.initials: SK
authors.lastname: Misra
authors.affiliation: Physics Department, Concordia University, 1455 de Maisonneuve Blvd West, Montreal, QC H3G 1M8, Canada.
authors.forename: S I
authors.initials: SI
authors.lastname: Andronenko
authors.affiliation: ACERT Biomedical Center, Baker Laboratory, Cornell University, Ithaca, NY 14853-1301, USA.
authors.forename: D
authors.initials: D
authors.lastname: Tipikin
authors.affiliation: ACERT Biomedical Center, Baker Laboratory, Cornell University, Ithaca, NY 14853-1301, USA.
authors.forename: J H
authors.initials: JH
authors.lastname: Freed
authors.affiliation: Department of Metallurgical Engineering and Material Science, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, India.
authors.forename: V
authors.initials: V
authors.lastname: Somani
authors.affiliation: Department of Metallurgical Engineering and Material Science, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, India.
authors.forename: Om
authors.initials: O
authors.lastname: Prakash
keywords: EPR; Fe3+ ion; Nanoparticle; TiO2; anatase; rutile