Ab initio hybrid DFT calculations of BaTiO₃ bulk and BaO-terminated (001) surface F-centers

Abstract

Using a supercell model and a hybrid B3PW exchange-correlation functional, we have performed first principles calculations for the F-center in the BaTiO3 bulk and on the BaO-terminated (001) surface. We find that two Ti atoms nearest to the bulk F-center are repulsed, while nearest eight oxygen and four barium atoms relax toward the oxygen vacancy (by 1.06, 0.71 and 0.08% of the lattice constant [Formula: see text], respectively). The magnitudes of atomic displacements around the F-center located on the BaO-terminated (001) surface in most cases (except for Ti) are larger than those around the bulk F-center (0.1, 1.4 and 1.0% of [Formula: see text], respectively). Our calculated BaTiO3 bulk [Formula: see text]–[Formula: see text] bandgap of 3.55 eV is in an acceptable agreement with the respective experimental bandgap value of 3.2 eV. The pristine BaO-terminated (001) surface [Formula: see text]–[Formula: see text] bandgap (3.49 eV) is reduced with respect to the bulk bandgap value. The bulk and BaO-terminated (001) surface F-center bands in BaTiO3 matrix are located only at 0.23 eV and 0.07 eV under the conduction band (CB) bottom, indicating that the F-center is a shallow donor. The F-center in the BaTiO3 bulk contains charge of 1.103[Formula: see text], whereas slightly less charge, only 1.052[Formula: see text], are localized inside the F-center on the BaO-terminated (001) surface. Our calculations demonstrate considerable increase of the chemical bond covalency between the BaTiO3 bulk F-center and its two nearest Ti atoms equal to 0.320[Formula: see text], and even larger increase for BaO-terminated (001) surface F-center and its nearest Ti atom 0.480[Formula: see text], in comparison to the relevant Ti–O chemical bond covalency in the perfect BaTiO3 bulk 0.100[Formula: see text]. The difference between F-center formation energy in BaTiO3 bulk (10.3 eV) and on the BaO-terminated (001) surface (10.2 eV) trigger the segregation of the F-center from the bulk toward the BaO-terminated (001) surface.

Ab initio Calculations of YAlO3 and ABO3 Perovskite (001), (011) and (111) Surfaces, Interfaces and Defects

“…Our B3PW calculated nearest atom displacements surrounding the F-center in ABO 3 perovskites are collected in Table III and compared with related results obtained for other ABO 3 perovskites [38][39][40][41]43]. As we can see from Table III, the two nearest to the Fcenter Ti atoms are by 1.06% of a 0 repulsed in the BaTiO 3 from the oxygen vacancy.…”

“…Finally, the ABO 3 perovskite, or for example, the BaTiO 3 bulk F-center calculations were carried out using 3 x 3 x 3 times extended supercell model. Such a supercell in our calculations contains 134 atoms as well as one isolated F-center defect [38,40,43].…”

“…Oxygen vacancy (V 0 ) (so-called neutral F-center) in ABO 3 perovskites traps two electrons. Experimental and theoretical investigations of F-centres in complex ABO 3 matrixes are a very important topic, since the F-center is the best known classical point defect, which strongly affects all material properties [37][38][39][40][41][42][43][44].…”

Comparative Ab initio Calculations for ABO3 Perovskite (001), (011) and (111) as well as YAlO3 (001) Surfaces and F Centers

“…Since the F-center is the best known classical point defect, which strongly affects all ABO3 perovskite properties, their theoretical and experimental investigation is a very hot topic. Nevertheless, most of the experimental and theoretical studies in the ABO3 perovskite materials are performed for the bulk F-center defects [20][21][22][23][24][25][26][27][28][29]. The BO2 and especially AO-terminated ABO3 perovskite (001) surface F-centers centers are considerably less studied both theoretically and experimentally.…”

Investigation of Improved Reliability in BaTiO3 -Based Ceramics via Two-Step Sintering by Impedance Spectroscopy and Schottky Barrier Model

“…It is worth to notice, that oxygen vacancies in BaTiO 3 bulk and on its BaO‐terminated (001) surface were recently studied theoretically by Sokolov et al Generally, the properties determined by the intrinsic and the extrinsic of grain boundaries are very different from that of inner grains, which is mainly due to segregation effect and stresses in the vicinity of grain boundaries. And in a broad range of oxide ceramics which exhibit ionic conduction, electric conduction, or mixed ionic–electric conduction, grain boundaries exhibit a pronounced blocking effect and play a role of barriers when charged carriers try to transfer from grains to grains.…”