Vacancies in ordered and disordered titanium monoxide: Mechanism of B1 structure stabilization

Abstract

The electronic structure and stability of three phases of titanium monoxide TiO y with B 1 type of the basic structure have been studied. Cubic phase without structural vacancies, TiO, and two phases with structural vacancies, monoclinic Ti 5 O 5 and cubic disordered TiO 1.0 , was treated by means of first-principles calculations within the density functional theory with pseudo-potential approach based on the plane wave's basis. The ordered monoclinic phase Ti 5 O 5 was found to be the most stable and the cubic TiO without vacancies the less stable one. The role of structural vacancies in the titanium sublattice is to decrease the Fermi energy, the role of vacancies in the oxygen sublattice is to contribute to the appearance of Ti–Ti bonding interactions through these vacancies and to reinforce the Ti–Ti interactions close to them. Listed effects are significantly pronounced if the vacancies in the titanium and oxygen sublattices are associated in the so called “vacancy channels” which determine the formation of vacancy ordered structure of monoclinic Ti 5 O 5 -type. Changes in total DOS of titanium monoxide when going from vacancy-free TiO to TiO with disordered structural vacancies and to TiO with ordered structural vacancies. • Ordered monoclinic Ti 5 O 5 is the most stable phase of titanium monoxide. • Vacancy-free TiO is the less stable phase of the titanium monoxide. • Ordering of oxygen vacancies leads to the appearance of Ti–Ti bonding interactions. • Titanium vacancies contribute significantly to the decreasing of the Fermi energy.