Enhanced electrocaloric effect in displacive-type organic ferroelectrics

Charles Kittel has written a masterpiece book, “Introduction to Solid State Physics” (ISSP). He mentions in the chapter on ferroelectrics in detail that barium titanate is the typical displacive-type ferroelectric compound where the Ti4+ displacement develops a dipole moment, which has made a deep impression in our mind. The author’s group, however, has arrived at an alternative viewpoint on the unit cell structure of barium titanate based on their exhaustive experimental studies. Accordingly, the author sent his relevant papers in 2006 and 2007 to Kittel. He endorsed the results frankly with reminiscence. He mentioned revising the ferroelectric chapter of ISSP according the author’s suggestions. It appears to be admissible to publish details now after Kittel has passed away. A long time misunderstanding of the phase transition in barium titanate is due to the text book knowledge of ISSP.

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Adjustable negative electrocaloric effect in Pb1+xZrO3 thin films

Journal of Materials Science Materials in Electronics ◽

10.1007/s10854-021-06462-9 ◽

2021 ◽

Author(s):

Yi Ye ◽

Fengzhen Huang ◽

Lin Lei ◽

Lin Liu ◽

Shuo Yan ◽

...

Keyword(s):

Thin Films ◽

Electrocaloric Effect

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A unified perturbative approach to electrocaloric effects

Communications Materials ◽

10.1038/s43246-021-00167-6 ◽

2021 ◽

Vol 2 (1) ◽

Author(s):

Mónica Graf ◽

Jorge Íñiguez

Keyword(s):

External Field ◽

Taylor Series ◽

Physical Interpretation ◽

Applied Field ◽

Atomistic Simulations ◽

Small Field ◽

Electrocaloric Effect ◽

Perturbative Approach ◽

Similarities And Differences ◽

Straightforward Interpretation

AbstractThe electrocaloric effect, that is, the temperature change experienced by an insulator upon application of an electric field, offers promising ecofriendly alternatives to refrigeration. However, the theoretical treatments of this response are mostly case specific and lack a unified picture revealing the similarities and differences among the various known effects. Here, we show that the electrocaloric effect lends itself to a straightforward interpretation when expressed as a Taylor series in the external field. Our formalism explains in a unified and simple way the most notable small-field effects reported in the literature, namely the so-called normal and inverse electrocaloric responses, corresponding to an increase or decrease of temperature under applied field, as usually found in ferroelectrics or antiferroelectrics, respectively. This helps us to clarify their physical interpretation. We then discuss in detail atomistic simulations for the prototype ferroelectric PbTiO3, explicitly evaluating subtle predictions of the theory, such as the occurrence of competing contributions to the electrocaloric response.

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Giant room temperature elastocaloric effect in metal-free thin-film perovskites

npj Computational Materials ◽

10.1038/s41524-021-00599-1 ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Cheng Li ◽

Yu Hui Huang ◽

Jian-Jun Wang ◽

Bo Wang ◽

Yong Jun Wu ◽

...

Keyword(s):

Thin Films ◽

Solid State ◽

Room Temperature ◽

Entropy Change ◽

Stress Change ◽

Chemical Doping ◽

Metal Free ◽

Organic Ferroelectrics ◽

Potential Applications ◽

Unit Stress

AbstractSolid-state refrigeration which is environmentally benign has attracted considerable attention. Mechanocaloric (mC) materials, in which the phase transitions can be induced by mechanical stresses, represent one of the most promising types of solid-state caloric materials. Herein, we have developed a thermodynamic phenomenological model and predicted extraordinarily large elastocaloric (eC) strengths for the (111)-oriented metal-free perovskite ferroelectric [MDABCO](NH4)I3 thin-films. The predicted room temperature isothermal eC ΔSeC/Δσ (eC entropy change under unit stress change) and adiabatic eC ΔTeC/Δσ (eC temperature change under unit stress change) for [MDABCO](NH4)I3 are −60.0 J K−1 kg−1 GPa−1 and 17.9 K GPa−1, respectively, which are 20 times higher than the traditional ferroelectric oxides such as BaTiO3 thin films. We have also demonstrated that the eC performance can be improved by reducing the Young’s modulus or enhancing the thermal expansion coefficient (which could be realized through chemical doping, etc.). We expect these discoveries to spur further interest in the potential applications of metal-free organic ferroelectrics materials towards next-generation eC refrigeration devices.

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