Abstract
The superlattice and domain structures exhibited by ordered titanium monoxide Ti5O5 are disrupted by low energy electron beam irradiation. The effect is attributed to the disordering of the oxygen and titanium sublattices. This disordering is caused by the displacement of both oxygen and titanium atoms by the incident electrons and results in a phase transformation of the monoclinic phase Ti5O5 into cubic B1 titanium monoxide. In order to determine the energies required for the displacement of titanium or oxygen atoms, i.e. threshold displacement energies, a systematic study of the disappearance of superstructure reflections with increasing electron energy and electron bombardment dose has been performed in situ in a transmission electron microscope (TEM). An incident electron energy threshold between 120 and 140 keV has been observed. This threshold can be ascribed to the displacements of titanium atoms with 4 as well as with 5 oxygen atoms as nearest neighbors. The displacement threshold energy of titanium atoms in Ti5O5 corresponding with the observed incident electron threshold energy lies between 6.0 and 7.5 eV. This surprisingly low value can be explained by the presence of either one or two vacant oxygen lattice sites in the nearest neighbors of all titanium atoms.
Highlights
The study of the vacancy defect structure and the order-disorder phase transformations in titanium oxides of different stoichiometry draw the increasing attention as their importance for synthesis of the materials with the distinct functional optical or electronic properties
The same low occupancy of lattice sites is found around each oxygen atom in titanium monoxide
The disordering of the monoclinic Ti5O5 phase under electron beam irradiation has been studied with transmission electron microscope (TEM)
Summary
The study of the vacancy defect structure and the order-disorder phase transformations in titanium oxides of different stoichiometry draw the increasing attention as their importance for synthesis of the materials with the distinct functional optical or electronic properties. The low- and high-temperature stability of the crystal structure (space group C2/m) of titanium monoxide Ti5O5 with a very high number of vacant crystal lattice sites[1] is of pivotal interest. Above 1223 K, both sublattices are disordered and the B1 structure (space group Fm-3m), with the same amount of vacant lattice sites of about 16.7 at.% becomes stable[1]. The same low occupancy of lattice sites is found around each oxygen atom in titanium monoxide. The superlattice reflections of TiOx, caused by the ordering of atomic-vacancy ordering, can be effectively removed under electron irradiation at 200 keV3. In order to determine the displacement threshold energy in Ti5O5, a systematic irradiation study of the ordered monoxide in a wide range of incident electron energies www.nature.com/scientificreports/. The data on threshold energies will give access to the strength of chemical bonds and clarify the nature of the remarkable thermal stability of the vacancy rich binary compound Ti5O5
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