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

Abstract

Structure-property relationships in ferroelectrics extend over several length scales from the individual unit cell to the macroscopic device, and with dynamics spanning a broad temporal domain. Characterizing the multi-scale structural origin of electric field-induced polarization reversal and strain in ferroelectrics is an ongoing challenge that so far has obscured its fundamental behaviour. By utilizing small intensity differences between Friedel pairs due to resonant scattering, we demonstrate a time-resolved X-ray diffraction technique for directly and simultaneously measuring both lattice strain and, for the first time, polarization reversal during in-situ electrical perturbation. This technique is demonstrated for BaTiO3-BiZn0.5Ti0.5O3 (BT-BZT) polycrystalline ferroelectrics, a prototypical lead-free piezoelectric with an ambiguous switching mechanism. This combines the benefits of spectroscopic and diffraction-based measurements into a single and robust technique with time resolution down to the ns scale, opening a new door to in-situ structure-property characterization that probes the full extent of the ferroelectric behaviour.

Nondestructive Method for the Determination of the Electric Polarization Orientation in Thin Films: Illustration on Gallium Ferrite Thin Films

“…They rely on the observation of the slight difference between the diffracted intensities of Friedel or Bijvoet pairs at one given wavelength and require highly precise intensity measurements, usually performed on single crystals . Recently, the electric field driven polarization inversion was evidenced in bulk ferroelectric BaTiO 3 ‐BiZn 0.5 Ti 0.5 O 3 ceramics through a tedious measurement of the diffracted intensities for the {111} reflections near the K‐edge of the Ba atom . We have chosen a different path to benefit from the possibilities offered by REXS, making use of the tunable energy of the synchrotron to record the intensity of a Bragg reflection as a function of the energy of the scattered photons crossing an atomic absorption edge.…”

“…Spectra are recorded for a significant number (≈15) of reflections over a broad range of energy around the chosen edges (±60 eV). This makes the method robust against any potential experimental artefacts and much easier to perform than the comparison of very similar diffraction intensities measured for only one reflection at one wavelength …”

Intrinsic Ferroelectricity in Charge-Ordered Magnetite

“…This principle has been used successfully by Azimonte et al [39], who observed an intensity difference of about 5% between the intensities of a reflection on multiferroic DyMn 2 O 5 after applying positive and negative electric fields, respectively. Resonant scattering has also been used to to reconstruct displacement of atoms in BaTiO 3 -based ferroelectric ceramics during polarization inversion [40]. An intensity difference of about 1% for 111 Bragg reflection was observed for two inversion-related polarization states.…”

“…The measurements then have to be conducted and time-resolved, with electronic coordination between voltage pulses, detector read-out and diffractometer movements. To this extent, we adapted a setup for time-resolved diffraction, which had been previously used primarily for studying piezoelectric samples, for the synchrotron beamline P09 [41] of PETRAIII [40,[42][43][44][45]. We chose a photon energy of 8.55 keV, sufficiently far above the Fe K edge to suppress resonant scattering effects and EXAFS (extended x-ray absorption fine structure) , but close enough to provide for a significant imaginary part of the Fe scattering factor.…”

“…To minimize current heating, we applied only small single pulses, as indicated in the top panel of Figure 5, rather than the PUND pulse train employed for the macroscopic measurements (Figure 3 top). During the measurements shown in Figure 5, the thermometer close to the sample displayed between 6 and 7 K, but the real sample temperature was likely higher, perhaps even exceeding 10 K. During switching, the position of the Bragg reflection may slightly move due to piezoelectricity [40,45]. In order to ensure that at each time the full integrated intensity is obtained, we used a wide open detector and collected a full time-resolved rocking curve.…”