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Title: Why is the electrocaloric effect so small in ferroelectrics?

Ferroelectrics are attractive candidate materials for environmentally friendly solid state refrigeration free of greenhouse gases. Their thermal response upon variations of external electric fields is largest in the vicinity of their phase transitions, which may occur near room temperature. The magnitude of the effect, however, is too small for useful cooling applications even when they are driven close to dielectric breakdown. Insight from microscopic theory is therefore needed to characterize materials and provide guiding principles to search for new ones with enhanced electrocaloric performance. Here, we derive from well-known microscopic models of ferroelectricity meaningful figures of merit for a wide class of ferroelectric materials. Such figures of merit provide insight into the relation between the strength of the effect and the characteristic interactions of ferroelectrics such as dipolar forces. We find that the long range nature of these interactions results in a small effect. A strategy is proposed to make it larger by shortening the correlation lengths of fluctuations of polarization. In addition, we bring into question other widely used but empirical figures of merit and facilitate understanding of the recently observed secondary broad peak in the electrocalorics of relaxor ferroelectrics.
Authors:
ORCiD logo [1] ;  [2]
  1. Argonne National Lab. (ANL), Argonne, IL (United States). Materials Science Division; Univ. of Costa Rica, San Jose (Costa Rica)
  2. Argonne National Lab. (ANL), Argonne, IL (United States); Univ. of Chicago, IL (United States). James Franck Inst.
Publication Date:
Grant/Contract Number:
AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
APL Materials
Additional Journal Information:
Journal Volume: 4; Journal Issue: 6; Journal ID: ISSN 2166-532X
Publisher:
American Institute of Physics (AIP)
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Contributing Orgs:
Univ. of Costa Rica, San Jose (Costa Rica); Univ. of Chicago, IL (United States)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Relaxor ferroelectrics; Electric fields; Polarization; Ferroelectric materials; Mean field theory
OSTI Identifier:
1356630

Guzmán-Verri, G. G., and Littlewood, P. B.. Why is the electrocaloric effect so small in ferroelectrics?. United States: N. p., Web. doi:10.1063/1.4950788.
Guzmán-Verri, G. G., & Littlewood, P. B.. Why is the electrocaloric effect so small in ferroelectrics?. United States. doi:10.1063/1.4950788.
Guzmán-Verri, G. G., and Littlewood, P. B.. 2016. "Why is the electrocaloric effect so small in ferroelectrics?". United States. doi:10.1063/1.4950788. https://www.osti.gov/servlets/purl/1356630.
@article{osti_1356630,
title = {Why is the electrocaloric effect so small in ferroelectrics?},
author = {Guzmán-Verri, G. G. and Littlewood, P. B.},
abstractNote = {Ferroelectrics are attractive candidate materials for environmentally friendly solid state refrigeration free of greenhouse gases. Their thermal response upon variations of external electric fields is largest in the vicinity of their phase transitions, which may occur near room temperature. The magnitude of the effect, however, is too small for useful cooling applications even when they are driven close to dielectric breakdown. Insight from microscopic theory is therefore needed to characterize materials and provide guiding principles to search for new ones with enhanced electrocaloric performance. Here, we derive from well-known microscopic models of ferroelectricity meaningful figures of merit for a wide class of ferroelectric materials. Such figures of merit provide insight into the relation between the strength of the effect and the characteristic interactions of ferroelectrics such as dipolar forces. We find that the long range nature of these interactions results in a small effect. A strategy is proposed to make it larger by shortening the correlation lengths of fluctuations of polarization. In addition, we bring into question other widely used but empirical figures of merit and facilitate understanding of the recently observed secondary broad peak in the electrocalorics of relaxor ferroelectrics.},
doi = {10.1063/1.4950788},
journal = {APL Materials},
number = 6,
volume = 4,
place = {United States},
year = {2016},
month = {5}
}