Department of Mechanical and Aerospace Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
Department of Chemistry, South University of Science and Technology of China, Shenzhen, 518055, China.
Sci Rep. 2017 Sep 11;7(1):11111. doi: 10.1038/s41598-017-11633-y.
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 (∆S) is limited by distinct correlation volumes (V ) and transition diffuseness. The linearity between V and the transition diffuseness is emphasized, while ∆S = 300 kJ/(K.m) is obtained for PbBaZrO. The ∆S in antiferroelectric PbZrTiO, PbBaZrO and polymeric ferroelectrics scales proportionally with V , owing to the one-dimensional structural constraint on lattice-scale depolarization dynamics; whereas ∆S in relaxor and normal ferroelectrics scales as ∆S ~ V , 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.
电卡（EC）材料在环保型固态制冷和可集成的片上热管理方面具有广阔的应用前景。虽然 EC 薄膜的直接测量仍然具有挑战性，但对于量化包括正常、弛豫体、有机和反铁电等丰富 EC 材料的冷却性能的通用理论框架是必不可少的，这对于开发新的灵活和室温冷却替代品至关重要。在这里，我们提出了一种通用的理论，将主方程与麦克斯韦关系相结合，并在 EC 材料的宏观冷却响应与相变的固有弥散度和相关特性之间建立了分析关系。在增加的电场下，EC 熵和绝热温度变化最初呈二次线性增加，然后进一步呈线性增长，并最终逐渐达到饱和。熵变（∆S）的上限受不同的相关体积（V）和相变弥散度限制。V 与相变弥散度之间的线性关系得到了强调，同时对于 PbBaZrO，∆S 达到了 300kJ/(K.m)。反铁电 PbZrTiO、PbBaZrO 和聚合物铁电体中的 ∆S 与 V 成正比，这是由于晶格尺度去极化动力学的一维结构约束；而弛豫体和正常铁电体中的 ∆S 则与 ∆S ~ V 成正比，这与 EC 材料中偶极相互作用指数为 2/3 和铁电畴壁的已证明的分数维数 2.5 相符。
