Diffraction Measurements with Electric Fields
Critus diffraction cells are designed to be used in a range of different ways. There primary purpose is for use in conjunction with lab-based or synchrotron XRD instrumentation. In this application, studies can vary from simply taking diffraction patterns at a set temperature and electric field, to full hardware synchronised time-resolved measurements. While not being used for diffraction measurements, Critus cells also operate as stand-alone electrical and electro-mechanical property measurement systems, providing a compact and user friendly test instrument for materials scientists.
In situ diffraction data tells us about the structural response of a material to an applied electric field. For example, there are several known mechanisms by which piezoelectric materials respond at different points in the polarisation and strain hysteresis, including lattice strain, domain volume fraction changes and phase transformations. All of these mechanisms are resolvable using diffraction measurements.
Methods of Usage
There are many ways in which the Critus diffraction cells can be used. Here, we simply highlight a few examples but hope that the user community also comes up with new and inventive ways of using our devices for the progression of scientific understanding in electrical and electro-mechanical materials.
Static Field and Temperature
This is likely the most basic type of in situ experiment that can be performed and is an extremely powerful tool for understanding the underlying structural mechanisms of material response. With a sample loaded in the cell, the temperature of interest is first set via the browser-based interface. An initial diffraction pattern is collected from the sample. Then a single electric field value is set, it may be above the coercive field in the case of a ferroelectric, and another diffraction pattern is collected. This structural information can then be used to directly ascertain the electric-field-induced structural change in the material.
Structural Change after Electric Field Cycle
This is an intermediate usage although also relatively simple to implement. As Critus diffraction cells also collect macroscopic electrical and electro-mechanical property data, changes in structure due to an electric field cycle can be observed and directly correlated to those properties. Here, an initial diffraction pattern is collected. Then, a waveform is setup such that some electric field process is to be done to the sample. During this waveform, the macroscopic property data is collected. On completion, an additional diffraction pattern is collected and compared with the original. In this way, the material property variations measured can be directly correlated to structural changes of the material. This type of data collection is ideally suited to studying processes such as poling and fatigue.
Time-Resolved Diffraction Measurements
This is an advanced use of Critus electric field cells. The user interface of the waveform setup also has embedded hardware synchronisation triggering options for the Critus cell to operate as either a master or slave to other instrumentation. For an XRD instrument, the "Trigger Out" options can be used for example to trigger an XRD detector system to collect diffraction data at specific points within the applied electric field cycle. in this way, the real-time structural variations can be directly correlated to the simultaneously collected macroscopic property data. Time-resolved experiments could be performed both in single-shot mode, or stroboscopic mode, where diffraction statistics can be built up over many cycles of a repetitive electric field waveform. This type of data collection is most likely performed at synchrotron sources, where synchronisation to other elements of the data acquisition system is required. it also offers the most thorough insight into the structure-property relationships of electrical and electro-mechanical response.