Atomic, strain and domain dynamics in ferroelectrics under cyclic electric field

Structural dynamics is a subject of a recent interest in solid state physics and a challenge for modern X-ray crystallography. Time-dependent response of solids to an external perturbation on atomic, mesoscopic and macroscopic length scales is the key to understanding many physical properties. We present the data-acquisition system (Gorfman et al., 2013) (DAQ) for X-ray diffraction study of repetitive micro- or millisecond dynamics in a broad range of materials (Gorfman, 2014) under cyclic perturbation. The DAQ operates on the principle of a multichannel analyser: it collects pulses from a single-photon-counting detector and resorts them between 10000 channels. Each channel corresponds to a certain time delay relative to the beginning of a latest perturbation cycle. The width of a channel (temporal resolution of the experiment) can be as small as 10 ns. We investigated atomic, strain and domain dynamics in SrxBa1-xNb2O6 single crystals: SBN50 (x=0.5, uniaxial ferroelectric) and SBN61(x=0.61, uniaxial relaxor ferroelectric). The experiments questioned the reason for large piezoelectric effect in uniaxial ferroelectrics where 180⁰ (inversion) domains are present, while non-180⁰ domains are absent. We applied triangular electric field (Figure 1) of variable frequencies and variable strengths. The time and electric field dependence of a set of Bragg rocking curves were followed: intensities, positions and peak widths were analysed giving access to atomic, strain and domain dynamics under external electric field. Figure 1. Left: contour plot of a -5 9 7 Bragg rocking curves from SBN50 single crystal collected under dynamically applied sub-coercive electric field. Right: dynamics of the peak position as a function of applied electric field, showing non-linear and hysteretic behaviour.

X-Ray induced Photostriction in Bismuth Ferrite

In a material with both a piezoelectric effect and the capability to form a photocurrent, photostriction can be observed - the deformation of the crystal by light. When studying photostriction, a potential method is to use x-rays to probe the unit cell in response to another light source as a stimulus, such as a laser or a diode. Given that x-rays are also photons it is plausible that they themselves produce some effect. An experiment was carried out to investigate how significant the effects of the x-rays are in producing photostriction in the absence of any other source of illumination. The material studied in this example was bismuth iron oxide, BiFeO3. A thin film with electrodes was used and it was found that the photocurrent generated by a laboratory x-ray source on the sample was of comparable level to that of a laser or diode used in the study of the bulk photoelectric effect. Using a novel, time dependent crystallographic approach, the intrinsic effect of synchrotron x-ray light on a photoferroelectric thin film has been investigated. Furthermore, we have simultaneously collected diffraction and photoelectric data, and the correlation between the electronic and structural properties will be discussed. These results could suggest that caution is necessary when interpreting photostriction data obtained with the use of x-rays.