2, Fraunhofer Institute for Ceramic Technologies and Systems, Dresden, , Germany
3, Technische Universität Dresden, Dresden, , Germany
Substantial efforts are being employed to the search and development of efficient and environmentally friendly materials with potential for solid state cooling. Motivated by recent discoveries, electrocaloric cooling might be a promising solution as an innovative refrigeration technique, as it shows a significant variation in temperature by adiabatically switching an applied electric field. Among them, lead-free thin films have raised an increased interest in research as they avoid the harmful effects of lead-containing materials. The purpose of our study is to investigate the electrocaloric effect in such lead-free epitaxial thin films. In particular, we are focusing on microstructural changes close to the phase transition of Na0.5Bi0.5TiO3 (NBT) in order to understand the basic mechanisms of the caloric effects, which might enable a further optimization of the electrocaloric properties for specific applications. Accordingly, the growth of NBT thin films with BaTiO3 and SrTiO3 additions is targeted to study the influence of the deposition parameters on the microstructural and the electrocaloric properties in this material system.
Therefore, NBT-based epitaxial thin films were grown by pulsed laser deposition on a variety of single crystalline substrates using LaxSr1-xCoO3 as a bottom electrode for a subsequent ferroelectric characterization. The structural characterization displays an epitaxial growth of NBT on the different substrates. Temperature and frequency dependence of the dielectric properties were assessed to measure the temperature of maximum permittivity Tm. Simultaneously, the electrocaloric temperature change was determined indirectly by the dependence of polarization on temperature and electric field strength. Finally, we will discuss the impact of the deposition parameters on the structural and functional properties of the grown films.
This work is supported by the DFG priority program 1599 “Ferroic cooling”