Wu Hong-Hui, Zhu Jiaming, Zhang Tong-Yi
Department of Mechanical and Aerospace Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
Phys Chem Chem Phys. 2015 Oct 7;17(37):23897-908. doi: 10.1039/c5cp02765a. Epub 2015 Aug 26.
Phase field modelling and thermodynamic analysis are employed to investigate depolarization and compression induced large negative and positive electrocaloric effects (ECEs) in ferroelectric tetragonal crystalline nanoparticles. The results show that double-hysteresis loops of polarization versus electric field dominate at temperatures below the Curie temperature of the ferroelectric material, when the mechanical compression exceeds a critical value. In addition to the mechanism of pseudo-first-order phase transition (PFOPT), the double-hysteresis loops are also caused by the abrupt rise of macroscopic polarization from the abc phase to the c phase or the sudden fall of macroscopic polarization from the c phase to the abc phase when the temperature increases. This phenomenon is called the electric-field-induced-pseudo-phase transition (EFIPPT) in the present study. Similar to the two types of PFOPTs, the two types of EFIPPTs cause large negative and positive ECEs, respectively, and give the maximum absolute values of negative and positive adiabatic temperature change (ATC ΔT). The temperature associated with the maximum absolute value of negative ATC ΔT is lower than that associated with the maximum positive ATC ΔT. Both maximum absolute values of ATC ΔTs change with the variation in the magnitude of an applied electric field and depend greatly on the compression intensity.
采用相场建模和热力学分析方法，研究了铁电四方晶纳米颗粒中去极化和压缩诱导的大的负电卡效应（ECE）和正电卡效应。结果表明，当机械压缩超过临界值时，在低于铁电材料居里温度的温度下，极化与电场的双滞回环起主导作用。除了准一级相变（PFOPT）机制外，双滞回环还由温度升高时宏观极化从abc相突然上升到c相或从c相突然下降到abc相引起。在本研究中，这种现象被称为电场诱导准相变（EFIPPT）。与两种类型的PFOPT类似，两种类型的EFIPPT分别导致大的负电卡效应和正电卡效应，并给出负绝热温度变化（ATC ΔT）和正绝热温度变化的最大绝对值。与负ATC ΔT最大绝对值相关的温度低于与正ATC ΔT最大绝对值相关的温度。ATC ΔT的两个最大绝对值都随外加电场强度的变化而变化，并且在很大程度上取决于压缩强度。
