Identification and study of vacancies in titanium monoxide by means of positron annihilation techniques

Abstract

Structural vacancies are of interest for an understanding of the crystal structure and the properties of metal oxides. Here we report on the identification and study of structural vacancies in titanium monoxide TiO_y with a B1 (NaCl) structure. Structural vacancies were identified by coincident Doppler broadening studies of the positron–electron annihilation radiation. The analysis shows that the nearest-neighbor atoms of vacancies are oxygen atoms. Taking into account the B1 structure of titanium monoxide this means that vacancies are located on the titanium sublattice. Positron trapping in titanium vacancies allows the study of the electronic structure of these vacancies by positron lifetime spectroscopy which shows that the valence electron density in the titanium vacancy increases with decreasing oxygen content y in TiO_y. The increase of the valence electron density is accompanied by a decrease of the mean number of nearest-neighbor oxygen atoms in the vicinity of the titanium vacancy from 6 to 5 atoms.