Polarization switching in BaTiO₃thin films measured by X-ray diffraction exploiting anomalous dispersion

Abstract

Films of BaTiO3 ranging from 20 nm to 300 nm in thickness were grown with pulsed laser deposition on Nb:SrTiO3. The quality of the layers was investigated using atomic force microscopy, X‐ray reflectivity and X‐ray diffraction. Both the micrographs and the X‐ray reflectivity spectra indicate a smooth surface of the layers. The X‐ray diffraction profiles measured using synchrotron radiation show features characteristic for highly crystalline thin films. The application of an external electric field parallel to the c axis changes an hkl reflection of BaTiO3 to an hk reflection. Due to the anomalous dispersion, the intensities of these two reflections are not equal and the atomic displacements can be determined from the intensity differences. The electric field‐induced intensity changes can be as large as a few percent, which makes data collection from a 100 nm film using Cu Kα radiation from an X‐ray tube feasible. The ΔI/I values of a number of reflections from the 20 and 50 nm films were measured using synchrotron radiation. The observed ΔI/I values were in good agreement with the intensity changes expected for polarization switching in the bulk.

Picometer polar atomic displacements in strontium titanate determined by resonant X-ray diffraction

“…To avoid ambiguities in the refinement, fixed structural models were presupposed or only one structural parameter was assumed to be unknown 35 , 36 . Often, the analysis required inverting (switching) the polarity of the structure 37 , 38 with an electric field in order to measure the Friedel pair contrast. This is not always feasible or may alter the material as in the present case.…”

Simultaneous resonant x-ray diffraction measurement of polarization inversion and lattice strain in polycrystalline ferroelectrics

“…Observing contrast between Friedel pairs requires highly precise measurements of diffraction intensities, and thus has been primarily applied in single crystals 26 and epitaxial thin films 27 28 . In the case of single crystals, absorption, extinction and multiple scattering often hinder precision, and successful applications of this remarkable technique are rare 26 27 28 29 . Both extinction and multiple scattering effects are absent in the case of powder diffraction because typical powder crystallites sizes are below the critical length of dynamical scattering.…”

Lattice Dynamics of Laser Excited Ferroelectric BaTiO3

“…The loss of the phase information during the scattering process is the reason for only being able to determine the relative change of the atoms from their initial position, but not the absolute polarization direction. Such distinction would only be possible by anomalous scattering [19]. Assuming a model, where the (positively charged) titanium atom moves antiparal-lel to the oxygen atoms in the surrounding octaeder, one would expect a decrease of the integrated intensity with increasing deviation of the titanium from the cell center and thus increasing field along the polarization.…”