Role of Ti Antisitelike Defects inSrTiO3

Abstract

Through first-principles calculations, the role of Ti antisitelike defects in the electrical and optical properties of SrTiO3 is proposed. Significant Ti off-centering from the Sr site toward the [100] or [110] direction leads to switchable polar states, and attractive interactions with the O vacancy drive them to form defect pairs. In these defect configurations, localized electronic states are introduced below the conduction band minimum. Our findings on Ti antisitelike defects suggest that they are responsible for the ferroelectricity and blue light emission in nonstoichiometric SrTiO3.

Effect of intrinsic point defects on ferroelectric polarization behavior of SrTiO3

“…The generalized gradient approximation Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional [31] is employed in the modified form for solids PBEsol [32] along with a plane wave cutoff energy of 400 eV. The rotationally invariant PBEsol + U approach is adopted with U eff = 4.36 eV on the Ti 3d orbitals that was shown to provide a good description of the electronic structure properties of SrTiO 3 with and without defects [10,23,33]. The ions are relaxed by applying a conjugate-gradient algorithm until the Hellmann-Feynman forces are less than 20 meV/Å with an optimized lattice constant of 3.903Å.…”

“…Sr and V O together with V Sr should be the most thermodynamically stable defects in SrTiO 3 under Ti-rich conditions [10,17,23], while the Ti-rich environment is predicted to be energetically more favorable than excess SrO in SrTiO 3 [23]. Sr indicating that the formation of the defect complex is energetically favored over the isolated defects.…”

“…This defect was predicted to be the dominant defect in SrTiO 3 along with the oxygen vacancy V O under Ti-rich conditions [10,23]. To find the most stable atomic configuration for Ti…”

“…Sr we examine the atomic structures with the Ti atom shifted [9,10]. The displaced Ti atom forms four Ti-O bonds of length 2.20Å that are much closer to the Ti-O bond distances in pristine SrTiO 3 (1.95Å).…”

“…Moreover, the emergence of net ferroelectric polarization was recently demonstrated for nanometer-thick films of SrTiO 3 [9] where this effect was attributed to electrically induced alignment of polar nanoregions that can naturally form because of the presence of intrinsic defects in SrTiO 3 crystals. It was previously demonstrated that intrinsic defects such as the antisite Ti defects can form in the bulk phase of Ti-rich SrTiO 3 , generate local polarization around the antisite Ti center due to an off-center displacement of the defect, and might contribute to the appearance of polar nanoregions [9,10] in a manner similar to extrinsic defects [11].…”