Electronic Structure of Pristine and Solute‐Incorporated SrTiO₃: III, Perfect‐Crystal, Grain‐Boundary Geometry, and Acceptor Doping

Abstract

Electronic structure is investigated for donor‐impurity‐incorporated perfect‐crystal and 36.8° symmetric tilt Sigma5 (310) grain‐boundary geometries of SrTiO3. The relaxed model of the atomic structure of the grain boundary used in the present investigations is the same as that used in Part II, as derived by Ravikumar et al. using lattice‐statics simulations based on pair‐potential calculations. As in Part II, the methodology of one‐electron first‐principle cluster calculations, which is discussed in Part I, is extended to clusters with single‐donor impurity substitutions at the central titanium and strontium sites. The effects of niobium substitution at a titanium site and lanthanum substitution at a strontium site in the bulk and at the grain‐boundary core have been investigated by determining the aspects of the electronic structure discussed for the acceptors. The influence of grain‐boundary crystallography on donor impurity incorporation has been evaluated in terms of variations in densities of states, spatial charge densities, and charge populations at the grain boundary. As in Parts I and II, no additional local lattice relaxations around the impurity are considered for the impurity‐incorporated clusters. Donor compensation mechanisms reported in the literature are discussed in connection with the electrical activity of the material. The calculations reveal that, in perfect‐crystal geometry, although lanthanum exhibits almost the expected donor behavior at the strontium site, niobium does not exhibit very good donor behavior at the titanium site. Moreover, a decrease in the donor behavior of these impurities is observed in the grain‐boundary geometry. Such variations in the electronic behavior of donors are due to the crystallographic variations at the grain boundary and are likely to decrease the grain‐boundary‐charge and associated space‐charge effects in the presence of donors as compared with the increase of such effects in the presence of acceptors. Consequently, a decrease in space‐charge‐induced segregation of donors at grain boundaries and the effects thereof can be expected.

First principles calculations of niobium substitution in strontium titanate

“…Doping the crystal with Nb introduces Nb d states which are split between the valence and conduction bands. A similar result was found by Rodrigues et al [5] although in their case the Nb d valence states were located 8 eV below the Fermi energy while in this letter the impurity band is centred around 6 eV and is significantly broader. The Nb d and O p states are also hybridized as indicated by the computed overlap population of the Nb-O bond which is 0.66.…”

“…There are, however, no first principles calculations which provide for deeper understanding of this behaviour. Rodrigues et al [5] have used the DV-Xα method to study Nb incorporation into the bulk and into the core of a [001] symmetric tilt boundary. However, they did not allow for atomic relaxation around the impurity and the model that they used for the tilt boundary structure was derived from an empirical pair potential calculation.…”

Electronic transport properties ofSrTiO3and its alloys:Sr1−xLaKınacı1, Sevik2, Çağın3 2010Phys. Rev. B494250View full textAdd to dashboardCite

“…They concluded that Nb as donor and Na as acceptor have the largest effect on the electrical conductivity. Rodrigues et al, 22 however, claimed the opposite for Nb doping in their embedded-cluster method study. In addition to the substitutions at cation ͑Sr, Ti͒ sites, Robertson 23 also discussed F, N, and S as substitutions for O using the results of tight-binding Green's-function method calculations.…”

Ab initiomolecular dynamics simulations of threshold displacement energies in SrTiO3

“…Characterization of radiation-induced defects therefore becomes an important aspect of understanding the radiation response of this material. Meanwhile, theoretical investigations of SrTiO 3 have been performed to study defect formation and migration energies and stable defect configurations, using both empirical atomic simulations and first-principles calculations [14][15][16][17][18]. However, the dynamics of atomic processes in SrTiO 3 under irradiation are not yet well understood.…”