Electrocaloric effect in lead-free Aurivillius relaxor ferroelectric ceramics
Electrocaloric effect in lead-free Aurivillius relaxor ferroelectric ceramics
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DOI：
10.1016/j.actamat.2016.11.001
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发表时间：
2017-02-01
期刊：
影响因子：
9.4
通讯作者：
Alford, Neil McN.
中科院分区：
文献类型：
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作者：
Axelsson, Anna-Karin;Le Goupil, Florian;Alford, Neil McN.
研究了一种基于SrBi₂(Nb₀.₂Ta₀.₈)₂O₉的无铅奥里维里斯相，以探索其在电热（EC）冷却系统中的潜在应用。事实证明，镨掺杂可有效地将最大介电常数所对应的温度从约300℃降低至80℃。镨掺杂还导致介电常数峰变宽以及其频率色散增加，这些都是强弛豫铁电体的典型特征。采用基于改进型差示扫描量热仪的直接测量系统，分析了致密的SrBi₁.₈₅Pr₀.₁₅(Nb₀.₂Ta₀.₈)₂O₉陶瓷的电热效应。与经典铁电体中观察到的趋势不同，在这种弛豫铁电体中，电热效应在远高于去极化温度的较宽温度范围内显著增加。这归因于由外电场诱导的极性纳米畴排列的作用。确定了进一步优化这种无铅弛豫体以使其成为高性能电热材料的方向。直接和间接电热测量之间的比较显示出显著差异，不仅在数值上，而且在趋势上。这些差异归因于奥里维里斯相的非遍历弛豫态，这种状态无法用麦克斯韦方程来描述。对于表现出此类特性的材料，预测电热效应的间接方法可能不可靠，需要通过直接的电热表征技术来测量电热效应。（C）2016 Acta Materialia Inc. 由Elsevier Ltd.出版。保留所有权利。
A lead-free Aurivillius phase based on SrBi2(Nb0.2Ta0.8)(2)O-9 was studied for potential application in electrocaloric (EC) cooling systems. Doping with praseodymium proved to be effective in reducing the temperature of maximum permittivity from about 300 degrees C to 80 degrees C. The praseodymium doping also led to a broadening of the permittivity peak and an increase in its frequency dispersion, which are typical features of strong relaxor ferroelectrics. A direct measurement system, based on a modified-differential scanning calorimeter, was used to analyze the EC effect of dense SrBi1.85Pr0.15(Nb0.2Ta0.8)(2)O-9 ceramics. Unlike the trend observed in classic ferroelectrics, the EC effect in this relaxor ferroelectric was found to increase significantly over a broad temperature range well above the temperature of depolarization. This was attributed to the contribution of the polar nanodomain alignment that is induced by the external electric field. Directions for further optimization of this lead-free relaxor towards a high-performing EC material were identified. A comparison between the direct and indirect EC measurements showed significant discrepancies, not only in a magnitude but also in the trend. These discrepancies were attributed to the non-ergodic relaxor state of the Aurivillius phase, which cannot be described with Maxwell equations. For materials displaying such characteristics indirect methods to predict EC effect may be unreliable requiring that the EC effect be measured by a direct EC characterization technique. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.