The electronic properties of SrTiO3-δ with oxygen vacancies or substitutions

Abstract

The electronic properties, including bandgap and conductivity, are critical for nearly all applications of multifunctional perovskite oxide ferroelectrics. Here we analysed possibility to induce semiconductor behaviour in these materials, which are basically insulators, by replacement of several percent of oxygen atoms with nitrogen, hydrogen, or vacancies. We explored this approach for one of the best studied members of the large family of ABO3 perovskite ferroelectrics — strontium titanate (SrTiO3). The atomic and electronic structure of defects were theoretically investigated using the large-scale first-principles calculations for both bulk crystal and thin films. The results of calculations were experimentally verified by studies of the optical properties at photon energies from 25 meV to 8.8 eV for in-situ prepared thin films. It was demonstrated that substitutions and vacancies prefer locations at surfaces or phase boundaries over those inside crystallites. At the same time, local states in the bandgap can be produced by vacancies located both inside the crystals and at the surface, but by nitrogen substitution only inside crystals. Wide-bandgap insulator phases were evidenced for all defects. Compared to pure SrTiO3 films, bandgap widening due to defects was theoretically predicted and experimentally detected.

Effects of Al Doping on Hydrogen Production Efficiency upon Photostimulated Water Splitting on SrTiO3 Nanoparticles

“…Moreover, the rest of the spin is distributed among the atoms on the same surface, but no atoms in all other layers (including the atoms in the central layer) change their spins at all. With respect to the spin localization not on the nearest to the defect atoms, we have already noted such a possibility concerning the neutral oxygen vacancies in the BaTiO 3 and SrTiO 3 …”

“…The Mulliken charge of Al 3+ ion here is +1.78|e| (compare with +1.92|e| for Al 4+ ion, see above). What is also important, V O in this defect does not produce donor energy levels below the conduction band bottom which is typical for the single V O defects in both bulk and slab STO. − Thus, two Al 3+ ions and one neutral oxygen vacancy, in a certain sense, “neutralize” each other, and complex defect Al– V O –Al almost does not change the STO band gap (indirect band gap of defective system is 3.27 eV cf. 3.36 eV for a perfect bulk STO), which is consistent with experimental data.…”

Dielectric behaviour of nitrogen doped perovskite SrTiO3−δNδ films

“…The regular stoichiometric films and the nitrogen-doped films were obtained in situ by controlling oxygen or nitrogen gas ambience, correspondingly, during the growth of the films by pulsed laser deposition. 39–41,50–53 The proper cationic composition and substitution of up to 10% of oxygen atoms with nitrogen were confirmed using several techniques. 50–53…”

“…37,38 Previously, we demonstrated significant changes in the electronic structure and in the optical and charge-transport properties caused by nitrogen substitution in STO. [39][40][41] The local structure and optical properties of nitrogen-doped STO were theoretically investigated using first-principles analysis. [41][42][43][44][45] However, explicit effects from nitrogen substitution on the dielectric constant in STO are unknown.…”

“…[39][40][41] The local structure and optical properties of nitrogen-doped STO were theoretically investigated using first-principles analysis. [41][42][43][44][45] However, explicit effects from nitrogen substitution on the dielectric constant in STO are unknown.…”