In this chapter, some alternative, "ferroic", solid-state energy conversion technologies are presented. These are the electrocaloric (pyroelectric), the barocaloric and the elastocaloric energy conversions. In their nature, they are analogous to magnetocaloric energy conversion; however, different external influences are needed to initialize the caloric effect. In the case of electrocaloric energy conversion, this is related to a change in the electric field; in the case of barocalorics, to a change in the hydrostatic pressure and in the case of elastocaloric energy conversion, to a change in the mechanical stress. Each group, to some extent, possesses possible advantages as well as some disadvantages in comparison with magnetocaloric energy conversion. However, since all three alternative solid-state energy conversion technologies are at an early stage of development, it is not yet reasonable to compare them with magnetocaloric energy conversion. It is only time and further research that will show the full potential of these alternative solid-state energy conversion technologies.This chapter is divided into three sections. In each section, the physical principle behind the discussed ferroic effect will be presented and an overview of existing materials with their physical properties will be made. Furthermore, different possibilities for designing an energy conversion device using these materials will be reviewed (especially for electrocalorics). However, since the technology based on these three effects is at an early stage of development, only a few prototypes of energy conversion devices have been presented.
Electrocaloric and Pyroelectric Energy ConversionIn this subsection, the electrocaloric and pyroelectric energy conversions are presented and discussed. In general, the electrocaloric energy conversion stands for the heat pumping processes (or refrigeration), whereas the pyroelectric energy conversion stands for the power generation.The underlying mechanism of the electrocaloric energy conversion is the so-called electrocaloric effect. The electrocaloric effect is expressed as the temperature change of dielectric materials subjected to a varying electric field. To simplify, as the electrocaloric material is subjected to a positive electric field change the material heats up, yet as the electric field is turned off the opposite occurs and the material cools down. Speaking thermodynamically, the electrocaloric effect is analogue to the magnetocaloric effect, though instead of the magnetic field change an electric field change is required to induce the caloric effect in the material. However, the electrocaloric energy conversion has some potential advantages over the magnetocaloric energy conversion, such as higher power density and higher compactness of the energy conversion devices, no dependence on rare-earth materials, no moving parts of the device, operation of the devices with less vibrations, silent operation, etc. Nevertheless, the area of the electrocaloric energy conversion only recently attracted m...
