Oxygen vacancy dipoles in strained epitaxial BaTiO3 films

Abstract

The existence of out-of-plane-oriented oxygen vacancy dipoles was experimentally established in (001) perovskite epitaxial films of ferroelectric barium titanate by analyses of the crystal and electronic structure as well as the ferroelectric and optical properties. The formation of the defects was shown to occur in the presence of in-plane compressive strain and oxygen-deficient deposition conditions. The in-plane compressive strain was suggested to favor the formation of oxygen vacancies V O in the Ba-O planes and thus stabilize the out-of-plane orientation of the dipolar (V +2 O-Ti 3+) + defects.

Anisotropic chemical expansion due to oxygen vacancies in perovskite films

“…2 h) agrees perfectly with this scenario. Notably, the NNO/LAO behavior is consistent with the out-of-plane dipolar orientation in compressively strained films of SrTiO 3 and BaTiO 3 , where in addition to the lattice expansion, an internal electric field also evidenced the dipolar orientation 11 – 13 . The out-of-plane dipoles correspond to vacancies in the [NdO] planes in NNO (Fig.…”

“…Epitaxial NNO films of ~ 20 nm in thickness were grown by pulsed laser deposition as described before 11 – 14 , 20 . To introduce oxygen vacancies, oxygen pressure of deposition, p O2 , was varied from 20 Pa for stoichiometric growth to as low as 0.1 Pa (see Methods section).…”

“…Here we focus on the poorly studied elastic properties of oxygen vacancies in AB O 3 perovskites. We have previously demonstrated that the elastic interactions of oxygen vacancies with substrate-imposed misfit strain can lead to a special spatial arrangement of the vacancies and thus stabilize epitaxial films of SrTiO 3 and BaTiO 3 11 – 14 . Both SrTiO 3 and BaTiO 3 are A 2+ B 4+ O 3 -type perovskites, where the formation of an oxygen vacancy (V O ) is associated with strong anisotropic lattice distortions.…”

In situ anion-doped epitaxial strontium titanate films

“…in the [Sr-O](001) planes. [7][8][9] This selective vacancy location is qualitatively comprehensible because the in-plane Ti-V O -Ti elongations ''work'' against the in-plane misfit compression that is energetically unfavorable. The strain-assisted favorable out-of-plane alignment of the local lattice Ti-V O -Ti elongations can result in a specific preferably out-of-plane macroscopic chemical expansion.…”

Oxygen Vacancies in Perovskite Oxide Piezoelectrics

“…Arrows show directions of the parameter change in ( a , b ). Plots are based on data reported in [ 47 , 48 ].…”