Landau-Devonshire理论探究不同类型铁电材料的电卡效应

Investigation into electrocaloric effect of different types of ferroelectric materials by Landau-Devonshire theory

近年来,低成本、高效、环保的电卡效应制冷材料得到了广泛研究,其中包括无机钙钛矿、有机钙钛矿、有机聚合物、分子铁电材料和二维铁电材料等.这些不同铁电材料的相变类型和电卡性能各异,而造成其差异的物理起源尚不明确.本文选择传统无机钙钛矿BaTiO3,PbTiO3和BiFeO3,有机钙钛矿[MDABCO](NH4)I3,有机聚合物P(VDF-TrFE),分子铁电体ImClO4和二维铁电体CuInP2S6这七种材料,利用Landau-Devonshire理论,研究并对比了其温变、熵变和电卡强度.通过分析自由能与极化之间的关系发现,在相变点附近,铁电材料的自由能势垒高度随温度的变化率越大,造成的极化随温度的变化率越高,而材料的电卡性能也越优异.本文揭示了不同类型铁电材料电卡性能差异的物理起源,为进一步开发具有高电卡性能的铁电材料提供理论指导.

The electrocaloric effects in various types of materials,including inorganic perovskites,organic perovskites,organic polymers,molecular ferroelectrics and two-dimensional ferroelectric materials,possess great potential in realizing solid-state cooling devices due to the advantages of low-cost,high-efficiency and environmental friendly.Different ferroelectric materials have distinct characteristics in terms of phase transition and electrocaloric response.The mechanism for enhancing the electrocaloric effect currently remains elusive.Here,typical inorganic perovskite BaTiO3,PbTiO3 and BiFeO3,organic perovskite[MDABCO](NH4)I3,organic polymer P(VDF-TrFE),molecular ferroelectric ImClO4 and two-dimensional ferroelectric CuInP2S6 are selected to analyze the origins of their electrocaloric effects based on the Landau-Devonshire theory.The temperaturedependent pyroelectric coefficients and electrocaloric performances of different ferroelectric materials indicate that the first-order phase transition material MDABCO and the second-order phase transition material ImClO4 have excellent performances for electrocaloric refrigeration.The predicted results also strongly suggest that near the phase transition point of the ferroelectric material,the variation rate of free energy barrier height with temperature contributes to the polarizability change with temperature,resulting in enhanced electrocaloric effect.This present work provides a theoretical basis and a new insight into the further development of ferroelectric materials with high electrocaloric response.