铁电铌酸钾钠中中间孪晶与自发极化理论
Theory of Intermediate Twinning and Spontaneous Polarization in Ferroelectric Potassium Sodium Niobate
AI总结：
针对铌酸钾钠相变路径与中间孪晶机制不明的问题，本文构建几何非线性电弹性能量模型，证明中间孪晶源于能量最小化，并解释多种实验微结构与自发极化。
摘要：
铌酸钾钠被认为是替代含铅铁电材料的一种重要材料体系。它表现出一级相变和铁电性，具有从能量转换到创新冷却技术的潜在应用，从而应对重要的社会挑战。然而，铌酸钾钠应用中的一个主要障碍是其多尺度非均质性，以及对其相变路径和微观结构缺乏理解。这可从 Pop-Ghe 等人（Ceram Int 47(14):20579-20585, 2021, https://doi.org/10.1016/j.ceramint.2021.04.067）的研究结果中看出，这些结果还揭示了他们称为相变过程中中间孪晶的现象。在此，我们证明中间孪晶是能量最小化的结果。我们为铌酸钾钠建立了一个几何非线性电弹性能量函数，包括立方-四方-正交相变和铁电性。极小化子的构造基于相容条件，这些条件确保连续变形和无极点界面。这些极小化子与实验观察结果一致，包括立方到四方相变下四方变体之间的层片、四方到正交相变下的交叉孪晶、中间孪晶以及自发极化。这表明完整的非线性电弹性模型如何为理解、探索和定制复杂铁电陶瓷的机电性能提供强有力的工具。
英文摘要：
Potassium sodium niobate is considered a prominent material system as a substitute for lead-containing ferroelectric materials. It exhibits first-order phase transformations and ferroelectricity with potential applications ranging from energy conversion to innovative cooling technologies, thereby addressing important societal challenges. However, a major obstacle in the application of potassium sodium niobate is its multi-scale heterogeneity and the lack of understanding of its phase transition pathway and microstructure. This can be seen from the findings of Pop-Ghe et al. (Ceram Int 47(14):20579-20585, 2021, https://doi.org/10.1016/j.ceramint.2021.04.067) which also reveal the occurrence of a phenomenon they term intermediate twinning during the phase transition. Here, we show that intermediate twinning is a consequence of energy minimization. We develop a geometrically nonlinear electroelastic energy function for potassium sodium niobate, including the cubic-tetragonal-orthorhombic transformations and ferroelectricity. The construction of the minimizers is based on compatibility conditions which ensure continuous deformations and pole-free interfaces. These minimizers agree with the experimental observations, including laminates between tetragonal variants under the cubic to tetragonal transformation, crossing twins under the tetragonal to orthorhombic transformation, intermediate twinning and spontaneous polarization. This shows how the full nonlinear electroelastic model provides a powerful tool in understanding, exploring, and tailoring the electromechanical properties of complex ferroelectric ceramics.
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