标题： 压电模仿压电效应 显示英文标题

标题： Piezoelectric mimicry of flexoelectricity

摘要： “巨大”压电效应的起源，其大小比理论预测大几个数量级，但经常被观察到，正受到密切关注。 有越来越多的证据表明，巨大的类似压电效应与寄生压电性有关，但不清楚压电性（由应变产生的极化）如何在典型的梁弯曲实验中模仿压电效应（由应变梯度产生的极化），因为在弯曲的梁中，净应变为零。 此外，与压电性不同，压电性在空间反演下会改变符号，这一标准应该能够区分这两种效应，但“巨大”压电效应对空间反演不敏感，似乎与压电性起源相矛盾。 在这里，我们证明，如果压电材料的压电系数在样品中不对称分布，它将产生一种由弯曲引起的极化，即使翻转样品也无法与真正的压电效应区分开来。 由压电性引起的有效压电系数在功能上与内在压电性相同，且通常更大：计算表明，对于标准钙钛矿铁电体，即使压电系数在1毫米范围内有1%的变化梯度，也足以产生一个1$\mu$C/m的巨大有效压电系数，比内在期望值大三个数量级。 显示英文摘要

摘要： The origin of "giant" flexoelectricity, orders of magnitude larger than theoretically predicted, yet frequently observed, is under intense scrutiny. There is mounting evidence correlating giant flexoelectric-like effects with parasitic piezoelectricity, but it is not clear how piezoelectricity (polarization generated by strain) manages to imitate flexoelectricity (polarization generated by strain gradient) in typical beam-bending experiments, since in a bent beam the net strain is zero. In addition, and contrary to flexoelectricity, piezoelectricity changes sign under space inversion, and this criterion should be able to distinguish the two effects and yet "giant" flexoelectricity is insensitive to space inversion, seemingly contradicting a piezoelectric origin. Here we show that, if a piezoelectric material has its piezoelectric coefficient be asymmetrically distributed across the sample, it will generate a bending-induced polarization impossible to distinguish from true flexoelectricity even by inverting the sample. The effective flexoelectric coefficient caused by piezoelectricity is functionally identical to, and often larger than, intrinsic flexoelectricity: the calculations show that, for standard perovskite ferroelectrics, even a tiny gradient of piezoelectricity (1% variation of piezoelectric coefficient across 1 mm) is sufficient to yield a giant effective flexoelectric coefficient of 1 $\mu$C/m, three orders of magnitude larger than the intrinsic expectation value.