Electric-field-induced local and mesoscale structural changes in polycrystalline dielectrics and ferroelectrics

Abstract

The atomic-scale response of dielectrics/ferroelectrics to electric fields is central to their functionality. Here we introduce an in situ characterization method that reveals changes in the local atomic structure in polycrystalline materials under fields. The method employs atomic pair distribution functions (PDFs), determined from X-ray total scattering that depends on orientation relative to the applied field, to probe structural changes over length scales from sub-Ångstrom to several nanometres. The PDF is sensitive to local ionic displacements and their short-range order, a key uniqueness relative to other techniques. The method is applied to representative ferroelectrics, BaTiO3 and Na½Bi½TiO3, and dielectric SrTiO3. For Na½Bi½TiO3, the results reveal an abrupt field-induced monoclinic to rhombohedral phase transition, accompanied by ordering of the local Bi displacements and reorientation of the nanoscale ferroelectric domains. For BaTiO3 and SrTiO3, the local/nanoscale structural changes observed in the PDFs are dominated by piezoelectric lattice strain and ionic polarizability, respectively.

Electric field dependent local structure of (KxNa1−x)0.5Goetzee-Barral1, Usher2, Stevenson3 et al. 2017Phys. Rev. B18040View full textAdd to dashboardCite

“…This inference received support from the recent in situ studies of field-induced structural changes in NBT using X-ray total scattering measurements during application of electric field [15]. The occurrence of the monoclinic-rhombohedral transition was evidenced both by Rietveld refinements using the diffraction patterns and by analysis of the corresponding PDFs which revealed abrupt changes in the distributions of Bi-Ti bond distances, consistent with subsequent reorientation of the rhombohedral ferroelectric domains expected upon poling [15].…”

“…The occurrence of the monoclinic-rhombohedral transition was evidenced both by Rietveld refinements using the diffraction patterns and by analysis of the corresponding PDFs which revealed abrupt changes in the distributions of Bi-Ti bond distances, consistent with subsequent reorientation of the rhombohedral ferroelectric domains expected upon poling [15].…”

“…The final displacement direction for every composition cannot be readily determined, however the shift to lower r of R2 in the perpendicular direction also suggests a final displacement approaching monoclinic. The remaining presence of R2 parallel to the field rules out a transition to a pure rhombohedral phase as was observed for NBT [15], or pure tetragonal, which for both examples would be observed as a lack of R2 altogether. These higher symmetry phases may be observable under greater electric fields.…”

“…The software Fit2D [22] was used to process the diffraction data. Totalscattering patterns incorporating contributions from crystallites having their Q hkl vectors parallel and perpendicular to the electric field were obtained by integrating ±10° sectors of the detector centred on the vertical and horizontal directions, respectively, as described in detail by Usher et al [15]. As demonstrated previously (Usher et al, 2015), a conventional formalism involving the sine Fourier transform, as implemented in the PDFgetX3 software…”

“…As discussed previously (Usher et al, 2015), a PDF obtained from directional total scattering, describes a distribution of all interatomic distances parallel to a given direction in the sample. This reflects smaller atomic displacement parameters and stronger correlation between the 8 atom-pairs forming the given peaks, as expected from the suppression of diffuse scattering.…”