Ba1-xSrxTiO3薄膜多卡效应的研究

The investigation of the electromechanical coupling driven multicaloriceffects in ferroelectric thin films is of great importance for improving refrigerating efficiency and further device applications. This research will concentrate on the multicaloric effects and the coupling effects of Ba1-xSrxTiO3 thin films controlled by strain and electric field based on the phenomenological Landau-Ginsburg-Devonshire theory and phase field model. The studies will be carried out to find the coupling mechanism between stress, electric field and caloric effect in ferroelectric thin films. Their multi-field coupling associated electrocaloric, elastocaloric, piezocaloric and flexocaloric properties will be described and proposed. Based on the results of theoretical analysis and numerical simulation, by proper choice of substrates, different components and domain structures and by using PLD and sol gel methods, Ba1-xSrxTiO3 thin films with different orientations and thicknesses will be prepared, and the relationship between electromechanical coupling and multicaloric properties will be obtained experimentally. By the combination of theoretical and experimental research, strain- electro- thermal coupling mechanism will be well clarified. The work will provide new theoretical and experimental guidance for solid state refrigeration based on multicaloric effects.

研究并调控力电耦合相关的多卡性能对提高电制冷效率和器件的实用化具有重要的意义。本项目拟开展应变和电场对铁电Ba1-xSrxTiO3薄膜多卡性能的影响规律以及相互耦合效应的研究。利用唯象非线性的Landau-Ginsburg-Devonshire 热力学理论及相场模型研究铁电薄膜的力、电、热耦合机理，预报多场耦合下的电卡、弹卡、压卡和挠卡性能。根据理论和数值模拟的结果，合理选择不同基底、不同组分和畴结构，利用 PLD 及溶胶凝胶法制备具有不同取向和厚度的铁电薄膜，从实验上给出力电多场耦合与材料多卡性能之间的关系。结合理论和实验研究，深入理解外场作用下的铁电薄膜材料力、电、热耦合机理，实现通过电场和应变共同控制和调节铁电薄膜的制冷性能，从而为铁电制冷材料及器件的设计提供理论和实验指导。

铁电材料的多卡制冷研究不仅具有重要的科学意义而且在下一代固态制冷领域具有很大的应用潜力，本项目在过去三年里主要研究基于铁电薄膜材料的多场耦合行为，以及力电耦合下的铁电材料的电卡、弹卡、压卡和挠卡效应。在Energy Environ. Sci.、Appl. Phys.Lett.、J. Appl. Phys.、Appl. Phys.A、Mater. Lett.、.等刊物发表SCI 论文13篇。具体研究成果如下：1) 用唯象热力学相变理论深入研究了外应力、应变梯度和热应力对铁电及多铁薄膜相变、多畴结构、顺电相挠卡效应、多卡等物性的调控; 2)建立了单相多铁薄膜材料力-电-热耦合的普遍性热力学理论框; 3)通过电场诱导薄膜材料面外发生相变, 0.5(Ba0.8Ca0.2)TiO3-0.5Bi(Mg0.5Ti0.5)O3无铅弛豫铁电薄膜中实现可以与文献所报道最大正电卡效应值相媲美的巨大负电卡效应，其最大温度变化值高达42度;4) 首次给出铁电体弹卡系数的公式，揭示负压电系数增强铁电体的弹卡效应，计算证明PVDF基铁电聚合物具有巨弹卡效应;5)使用了3种经典的机器学习算法: k近邻(k-Nearest Neighbours, k-NN)，支持向量机(Support Vector Machine, SVM)以及深度神经网络(Deep neural networks, DNNs)对K1-xNaxNbO3薄膜的温度-失配应变相图进行预测分类，这3种分类算法都具有十分良好的预测准确率达到了99%左右。这体现了机器学习在铁电相图预测分类中的可行性与可信度。