Local Investigations of the Electrocaloric Effect 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 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/><br/>Scanning Thermal Microscopy is emerging as a powerful Atomic Force Microscope based platform for mapping dynamic temperature distributions on the nanoscale. To date, however, spatial imaging of temperature changes in electrocaloric materials using this technique has been very limited. We build on the work of previous studies to show that Scanning Thermal Microscopy can be used to spatially map electrocaloric temperature changes on microscopic length scales, here demonstrated in a commercially obtained multilayer ceramic capacitor. In our approach, the electrocaloric response is measured at discrete locations with point-to-point separation as small as 150nm, allowing for reconstruction of spatial maps of heating and cooling as well as their temporal evolution. This technique offers a means to investigate electrocaloric responses at sub-micron length scales, which cannot easily be accessed by the more commonly used infra-red thermal imaging approaches. 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.