Agreement No: lzp-2020/2-0080

Duration: 2020 - 2021

Project Leader: Institute of Solid State Physics, University of Latvia, Dr.hab.Andris Šternbergs

Total budget: 100 389 EUR

Project description:

The project is devoted to study of lead-free ferroelectric materials for application in new generation of cooling devices, based on electrocaloric effect (ECE) and, in such a way, stimulates development and the following implementation in manufacturing of eco-innovative products. Success of this application crucially depends on materials, possessing high values of temperature change (DT), created by ECE. In spite of intensive studies of ECE, the results, which are obtained mostly by the indirect method, are controversial and suffer from weak understanding of mechanisms responsible for ECE, especially in high electric field range (at 100 kV/cm and above). Remarkably, the promising for practical application values of DT are observed in few researched devoted to bulk ferroelectrics exactly in such high electric fields. The goal of the project is to study ECE in high field range by direct measurements, focusing on bulk samples of Na0.5Bi0.5TiO3-based compositions in the region of morphotropic phase boundary, as well as to get a deeper insight into relationship between DT and polarization, what is important to make the search for materials, promising for practical applications, more purposeful. 

Results of project:

The electrocaloric effect in some NBT-based ferroelectrics has been studied in fields ranging up to 100 kV/cm. The highest value of DT (1.1 oC at 67 kV/cm) is found in composition 094NBT-0.06BT, located at the morphotropic phase boundary. An entropy jump at field induced 1st order phase transition significantly contributes to the total value of DT. In compositions where 1st order phase transition is suppressed, DT values are much lower. It is shown that polarization, which may be determined in different ways, is not mutually consistent. The nature of polarization in ferroelectric and relaxor states is not conducive to applying the Maxwell relation. No negative electrocaloric effect, as frequently reported in NBT and obtained by indirect methods, was observed found in the studied compositions.