Abstract
We investigate the effect of polar Sr–O vacancy pairs on the electric polarization of SrMnO3 (SMO) thin films using density functional theory (DFT) calculations. This is motivated by indications that ferroelectricity in complex oxides can be engineered by epitaxial strain but also via the defect chemistry. Our results suggest that intrinsic doping by cation and anion divacancies can induce a local polarization in unstrained non-polar SMO thin films and that a ferroelectric state can be stabilized below the critical strain of the stoichiometric material. This polarity is promoted by the electric dipole associated with the defect pair and its coupling to the atomic relaxations upon defect formation that polarize a region around the defect. This suggests that polar defect pairs affect the strain-dependent ferroelectricity in semiconducting antiferromagnetic SMO. For metallic ferromagnetic SMO we find a much weaker coupling between the defect dipole and the polarization due to much stronger electronic screening. Coupling of defect-pair dipoles at high enough concentrations along with their switchable orientation thus makes them a promising route to affect the ferroelectric transition in complex transition metal oxide thin films.
Highlights
We investigate the effect of polar Sr–O vacancy pairs on the electric polarization of SrMnO3 (SMO) thin films using density functional theory (DFT) calculations
Our results suggest that intrinsic doping by cation and anion divacancies can induce a local polarization in unstrained non-polar SMO thin films and that a ferroelectric state can be stabilized below the critical strain of the stoichiometric material
FeTi–VO defects are able to align in the direction of the lattice polarization in ferroelectric PbTiO3.8 VPb–VO divacancies are an important source of local polarization in Pb-containing perovskite oxides such as PbTiO3, where a VPb– VO concentration of 1.7% can induce a reduction of the ferroelectric transition temperature by about 35 K.18,19
Summary
Ferroelectricity in complex perovskite oxides has attracted great interest due to potential applications of ferroelectric thin films for various information storage technologies, such as non volatile random access memories and high-density data storage devices.[1,2,3] Point defects are promising to tailor the functional properties of oxides.[4,5,6,7,8,9,10,11,12,13,14] In particular, they can affect the polarization response in ferroelectrics by controlling the local polarization and the mechanism and kinetics of polarization switching.[15,16] Defect pairs such as cation–anion divacancies or vacancies coupled with substitutional atoms were shown to play an essential role in determining polarization properties.[17]. FeTi–VO defects are able to align in the direction of the lattice polarization in ferroelectric PbTiO3.8 VPb–VO divacancies are an important source of local polarization in Pb-containing perovskite oxides such as PbTiO3, where a VPb– VO concentration of 1.7% can induce a reduction of the ferroelectric transition temperature by about 35 K.18,19 defect pairs can promote ferroelectricity in paraelectric materials: off-centered antisite-like defects consisting of a Sr vacancy and an interstitial Ti atom or by one Ti/Sr antisite defect coupled to an oxygen vacancy or even by Sr–O–O trivacancies are believed to play a pivotal role for emerging room-temperature ferroelectricity in SrTiO3 thin films.[20,21,22,23]
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