Diffraction studies under in situ electric field using a large-area hybrid pixel XPAD detector

A new experimental approach to perform in situ electric field diffraction on single crystals using an on-then-off pump–probe mode in situ (i.e. the field-switching method) with a synchrotron or a laboratory X-ray source is presented. Taking advantage of the fast readout of the XPAD hybrid pixel two-dimensional detector and its programmable functionalities, the operation mode of the detector has been customized to significantly increase the efficiency of the method. The very weak electric field-induced structural response of a piezoelectric crystal can be accurately measured. This allows the piezoelectric tensor to be precisely obtained from Δθ shifts while the structural variations can be modelled using a full set of ΔI/I data. The experimental method and methodology are detailed and tested as a case study on pure piezoelectric compounds belonging to the α-quartz family (SiO2 and GaAsO4 single crystals). Using the two scan modes developed, it is demonstrated that tiny Bragg angle shifts can be measured as well as small field-induced Bragg intensity variations (<1%). The relevance of measurements performed with an X-ray laboratory source is demonstrated: partial data sets collected at synchrotrons can be completed, but more interestingly, a large part of the study can now be realized in the laboratory (medium to strong intensity reflections) in a comparable data collection time.