Nonlinearity in the high-electric-field piezoelectricity of epitaxial BiFeO3 on SrTiO3

Abstract

The piezoelectricity of a multiferroic BiFeO 3 thin film deviates from its low-field linear response in electric fields higher than 150 MV/m. Time-resolved synchrotron x-ray microdiffraction reveals a low-field piezoelectric coefficient of 55 pm/V and a steeper increase in strain at higher fields, with an effective piezoelectric coefficient of 86 pm/V. The strain reaches 2% at 281 MV/m, a factor of 1.3 higher than expected based on an extrapolation from low fields. The peak intensity of the BiFeO 3 (002) Bragg reflection decreases throughout the high-electric-field regime, accompanied by increased diffuse scattering, consistent with lattice softening lattice near a field-induced phase transition. V

Electrical phase diagram of bulkBiFeO3

“…At high values of the field, the system undergoes a drastic increase of the c parameter, reaching a strain of 4% at E ∼0.5 GV/m; at 0.3 GV/m the strain is about 2%, in nice agreement with the experimental data of Ref. 22. Such a strongly nonlinear behavior (the hypothetical linear regime is represented by a thin dashed line, for comparison) is clearly a consequence of lattice softening in proximity of the Cc-II phase, confirming the arguments of Chen et al -as we said, the transition itself occurs in our calculations at fields (0.69 GV/m) that are only slightly larger than those shown in Fig.…”

“…This may be within experimental reach (values up to 0.28 GV/m were probed in Ref. 22), and thus open new opportunities for the study of the supertetragonal phase of BiFeO 3 .…”

“…(Strictly speaking, our data should be compared with some caution to those of Ref. 22: in the latter the in-plane lattice parameters are clamped to the substrate, and do not show any variation with the applied field; in our computational experiment, all structural parameters of the cell are left free to relax. )…”

“…Interestingly, such information can also be used to access important functional properties of BiFeO 3 , and their evolution under an external field of arbitrary magnitude. For example, a recent experimental work has reported a significant nonlinearity in the electromechanical response of BiFeO 3 , with an increase of the piezoelectric coefficient at high fields; 22 we shall address this topic in the last part of this Section. Fig.…”

“…Chen et al 22 have recently studied the piezoelectricity of a BiFeO 3 thin film, and found that at high electric fields the response deviates significantly from the lowfield values. In particular, the out-of-plane strain component displays a strong nonlinearity, reaching values of up to 2% at the highest fields (0.28 GV/m); consequently, the piezoelectric constant increases from 55 pm/V up to 86 pm/V.…”