Extraordinarily Large Electrocaloric Strength of Metal‐Free Perovskites

Abstract

The availability of materials with high electrocaloric (EC) strengths is critical to enabling EC refrigeration in practical applications. Although large EC entropy changes, ΔSEC, and temperature changes, ΔTEC, have been achieved in traditional thin‐film ceramics and polymer ferroelectrics, they require the application of very high electric fields and thus their EC strengths ΔSEC/ΔE and ΔTEC/ΔE are too low for practical applications. Here, a fundamental thermodynamic description is developed, and extraordinarily large EC strengths of a metal‐free perovskite ferroelectric [MDABCO](NH4)I3 (MDABCO) are predicted. The predicted EC strengths: isothermal ΔSEC/ΔE and adiabatic ΔTEC/ΔE for MDABCO are 18 J m kg−1 K−1 MV−1 and 8.06 K m MV−1, respectively, more than three times the largest reported values in BaTiO3 single crystals. These predictions strongly suggest the metal‐free ferroelectric family of materials as the best candidates among existing materials for EC applications. The present work not only presents a general approach to developing thermodynamic potential energy functions for ferroelectric materials but also suggests a family of candidate materials with potentially extremely high EC performance.

Improper molecular ferroelectrics with simultaneous ultrahigh pyroelectricity and figures of merit

“…At a steady state, the variation of energy with order parameters was taken to be zero; therefore, ∂ G Experimental P S -T data were fitted on the above equation to derive the values of the coefficients  0 ,  11 ,  111 ,  1 ,  1 , and  2 , with the assumption that  0 and  11 depend on environmental factors/ experimental conditions.  111 is considered to be temperature dependent, and low-temperature quantum effects were incorporated in  1 and  111 in the calculation (43). Therefore, at temperatures above T C ,  111 is given as  111 = a 111 (T) (11) whereas at temperatures below T C ,  1 and  111 take the form…”

Metal‐Free Organic Halide Perovskite: A New Class for Next Optoelectronic Generation Devices

“…Wang et al presented a basic thermodynamic description for the metal-free perovskite MDABCONH 4 I 3 and predicted a very large electrocaloric (EC) refrigeration strength. [30] Under a relatively low electric field change of 2 MV m −1 and 1 GPa pressure, an EC entropy change of 36 J kg −1 K −1 and an EC temperature change of 16 K were achieved ( Figure 6H), leading to record-high EC strengths of isothermal and adiabatic ΔS EC / ΔE = 18 J m kg −1 K −1 MV −1 and ΔT EC /ΔE = 8.06 K m MV −1 , respectively. Both values are three times higher than those from crystals of the conventional, state-of-the-art, ferroelectric BaTiO 3 .…”

Performance characterization and application of composite adsorbent LiCl@ACFF for moisture harvesting

“…Recently, new porous matrix inspired the investigation of high-performance composite adsorbents, like hydrogels 24 and aerogels which usually provide large pore volumes to contain more hygroscopic salts. However, hydrogels tend to have drawbacks of low specific surface area, and swelling after adsorbing moisture 5 . Alternatively, ACFF is intensively used in numerous applications 23 – 28 like water treatment, gas separation, with advantages of extremely high surface area 29 , easy-to-be-shaped mechanical properties 25 , better adsorption characteristics, fast adsorption kinetics 30 and uniform micropore distribution to provide strong capillary strength for water adsorption.…”