Towards Spatially Resolved Mapping of the Electrocaloric Effect with Nanoscale Resolution using Scanning Thermal Microscopy

The electrocaloric effect is a well-known phenomenon where adiabatic application of an external electric field to a material results in a reversible temperature change. Interest in using these materials for environmentally friendly solid-state refrigeration applications has been rejuvenated by the discovery of this effect in commercially available multilayer ceramic capacitors and of giant electrocaloric effects in thin films. While the electrocaloric effect can be well described macroscopically through a thermodynamic approach and is understood to arise from changes in dipolar configurational entropy, the effect at the microscopic scale is not as well characterised. To date, infrared cameras represent the best spatial resolution available for in-situ imaging of temperature fields associated with electrocaloric effects, but features are limited in detail to the level of a few microns.<br/>In this work, we build on previous Scanning Thermal Microscopy studies of electrocaloric materials and demonstrate how this imaging mode can be adapted to measure local electrocaloric response with sub-micron resolution, here demonstrated in a multilayer ceramic capacitor. At a given point on the surface, the tip monitors the temperature while an electric field applied via the capacitor electrodes is cycled on and off. Once the measurement is complete, the tip moves to a neighbouring location and the field cycling and temperature recording process is repeated. Iterating this process across the surface allows for an MxN grid of temperature versus time plots to be created. From this data, the electrocaloric heating and cooling can be extracted to create 2D maps of the electrocaloric response, here demonstrated using a multilayer ceramic capacitor. We intend to use this technique to elucidate the behaviour of other electrocaloric materials and to examine the influence of microstructural inhomogeneity on electrocaloric response.