标题： 块体铁电材料中的强非线性柔电效应 显示英文标题

标题： Strong Nonlinear Flexoelectricity in Bulk Ferroelectrics

摘要： 应变梯度诱导的介电材料中的.flexoelectric效应对于机电作动和传感系统非常理想。 广泛采用的观点是，.flexoelectric极化对应变梯度呈线性响应，而不考虑非线性。 因此，非线性.flexoelectric效应在机电系统中的意义仍不清楚。 在此，我们建立了.flexoelectric效应的非线性本构模型，并提出了通过高阶谐波生成定量测量其非线性的策略。 在块状铁电材料中发现了强烈的非线性.flexoelectric效应，并确定了其系数，这由谐波对应变梯度的非线性依赖关系所证明。 基于此，我们说明非线性.flexoelectric效应表现出一种功能，可以将混合机械激励转换为具有差频和和频特征的相干电信号，从而在频率转换的信号处理中提供应用。 这些发现强调了铁电材料中非线性.flexoelectric效应的重要性，并为基于非线性.flexoelectric效应设计机电换能器开辟了新的机会。 显示英文摘要

摘要： Flexoelectricity induced by strain gradient in dielectrics is highly desirable for electromechanical actuating and sensing systems. It is broadly adopted that flexoelectric polarization responds linearly to strain gradient without considering nonlinearity. Consequently, the implication of nonlinear flexoelectricity in electromechanical systems remains unclear. Herein, we establish a nonlinear constitutive model for flexoelectricity and thereby propose a strategy for quantitatively measuring its nonlinearity through the high-order harmonic generations. A strong nonlinear flexoelectricity in bulk ferroelectrics is revealed and its coefficient is determined, as evidenced by their nonlinear dependence of harmonics on strain gradient. On this basis, we illustrate the nonlinear flexoelectricity manifests a functionality to transduce mixed mechanical excitations into coherent electrical signals featuring difference- and sum-frequencies, thereby offering utilization in signal processing for frequency conversion. These findings emphasize the significance of nonlinear flexoelectricity in ferroelectrics and open up new opportunities for designing electromechanical transducer based on nonlinear flexoelectricity.