A scaling law for distinct electrocaloric cooling performance in low-dimensional organic, relaxor and anti-ferroelectrics

Abstract

Electrocaloric (EC) materials show promise in eco-friendly solid-state refrigeration and integrable on-chip thermal management. While direct measurement of EC thin-films still remains challenging, a generic theoretical framework for quantifying the cooling properties of rich EC materials including normal-, relaxor-, organic- and anti-ferroelectrics is imperative for exploiting new flexible and room-temperature cooling alternatives. Here, we present a versatile theory that combines Master equation with Maxwell relations and analytically relates the macroscopic cooling responses in EC materials with the intrinsic diffuseness of phase transitions and correlation characteristics. Under increased electric fields, both EC entropy and adiabatic temperature changes increase quadratically initially, followed by further linear growth and eventual gradual saturation. The upper bound of entropy change (∆Smax) is limited by distinct correlation volumes (Vcr) and transition diffuseness. The linearity between Vcr and the transition diffuseness is emphasized, while ∆Smax = 300 kJ/(K.m3) is obtained for Pb0.8Ba0.2ZrO3. The ∆Smax in antiferroelectric Pb0.95Zr0.05TiO3, Pb0.8Ba0.2ZrO3 and polymeric ferroelectrics scales proportionally with Vcr −2.2, owing to the one-dimensional structural constraint on lattice-scale depolarization dynamics; whereas ∆Smax in relaxor and normal ferroelectrics scales as ∆Smax ~ Vcr −0.37, which tallies with a dipolar interaction exponent of 2/3 in EC materials and the well-proven fractional dimensionality of 2.5 for ferroelectric domain walls.

Analytical description of the size effect on pyroelectric and electrocaloric properties of ferroelectric nanoparticles

“…Electrocaloric (ECE) and pyroelectric (PEE) effects that are inherent to ferroelectrics are the subjects of intensive experimental and theoretical studies [27,28,29]. Electrocaloric (EC) and pyroelectric (PE) properties of ferroelectrics at ferroelectric-antiferroelectric phase boundaries [30], ferroelectric thin films [31,32,33,34], multilayers [35,36,37] and other low-dimensional materials [38] can be very different from those of single crystals [39].…”

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Using Landau-Ginzburg-Devonshire theory and effective medium approximation, we analytically calculate typical dependences of the pyroelectric and electrocaloric coefficients on external electric field, temperature and radius for spherical single-domain ferroelectric nanoparticles. The considered physical model corresponds to the nanocomposite with small fraction of ferroelectric nanoparticles.Within the framework of the analytical model we establish how the size changes determine the ferroelectric thin films [31, 32, 33, 34], multilayers [35, 36, 37] and other low-dimensional materials [38] can be very different from those of single crystals [39].As it is known [40,41], the polar materials in adiabatic conditions are characterized by the PEE (charge or electric field generation under temperature change) and by the inverse ECE (temperature change under application or removal of an electric field). The vivid manifestation of PEE and ECE in ferroelectrics is a consequence of the strong temperature dependence of the spontaneous polarization [42,43,44], especially in the vicinity of phase transitions [45,46] or near the morphotropic phase boundary [47].

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“…Within the framework of the analytical model we establish how the size changes determine the ferroelectric thin films [31, 32, 33, 34], multilayers [35, 36, 37] and other low-dimensional materials [38] can be very different from those of single crystals [39].…”

The dielectric and electrical proprieties of Ethylcarbazole family based copolymer

“…Polymers have been widely used as dielectric materials due to their ease of processing, permitting them to be formed into flexible films 13 . On other hand, high dielectric constant and low dielectric loss polymers are highly desired for advanced electrical applications, such as film capacitors 14 , artificial muscle 15 , and electrocaloric cooling 16 . However, there is no detail studies about dielectric proprieties of carbazole based copolymers such as Ethylcarbazole Poly(Ethylcarbazole-Terphenyl) (PEcbz-Ter),…”

Electrocaloric effect in cubic Hubbard nanoclusters

“…In addition, the techniques necessary to measure the ECE-related quantities are undergoing constant development 12 , 13 . Simultaneous efforts concern mastering the theoretical description and modelling of ECE 14 – 24 .…”