Investigation of Structural Vacancies in Titanium Monoxide
by Electron-Positron Annihilation

A. A. Valeeva^a*, A. A. Rempel’^a, W. Sprengel^b, and H.-E. Schaefer^c

^a Institute of Solid State Chemistry, Ural Division Russian Academy of Sciences,
ul. Pervomaskaya 91, Yekaterinburg, 620041, Russia

*e-mail: valeeva@ihim.uran.ru

^b Institute of Materials Physics, Graz University of Technology, Petersgasse 16, Graz, 8010 Austria

^c Institut für Theoretische und Angewandte Physik, Universität Stuttgart, Pfaffenwaldring 57, Stuttgart, 70569 Germany

Received October 14, 2008

Abstract—Local atomic environment of vacancies in nonstoichiometric titanium monoxide ranging in compo-
sition from TiO_0.74 to TiO_1.26 was studied by electron–positron annihilation. Analysis of the Doppler broadening
spectra of the annihilation gamma line for titanium and liquid oxygen showed that positrons in titanium mon-
oxide are trapped by titanium vacancies. Experiments revealed that the lifetime of positrons in ordered and dis-
ordered titanium monoxide TiO_y increases with increasing oxygen content y and varies from 184 to 210 ps. Data
on the valence electron density permitted the prediction that the lifetime of free positrons in stoichiometric tita-
nium monoxide is about 140 ps and the lifetime of positrons localized in an oxygen vacancy is about 170 ps.
The method used to analyze the gamma-line Doppler broadening spectra makes it possible to determine the type
and number of atoms around a vacancy and to investigate order–disorder phase transformations in nonstoichi-
ometric compounds.

PACS numbers: 78.70.Bj, 61.72.jd

DOI: 10.1134/S1063783409050060

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