Mechanical switching in ferroelectrics by shear stress and its implications on charged domain wall generation and vortex memory devices

Recently, the resurgence of interest in flexoelectricity in solids has promoted research on switching of ferroelectric domains via mechanical loads. In this work, combining thermodynamic calculation and phase-field simulation, we revealed that mechanical switching of polarization can be achieved in ferroelectrics by shear stress via a simple mechanism where the presence of flexoelectricity is not necessary. The switching is a consequence of the trilinear coupling between shear stress and the two polarization components that lie in the shear strain plane. Specifically, when the direction of one polarization component is fixed, switching of the other component can be induced by applying a shear stress. Moreover, when the shear stress is fixed, switching of one of the polarization components can lead to the switching of the other component. Phase diagrams of the stable polarization state as a function of shear stress, temperature and electric field are calculated. Furthermore, as demonstrated by phase-field simulation on a ferroelectric thin film, domain switching can indeed be realized by a local shear stress. Importantly, the combining effect of shear stress and electric field can lead to a deterministic writing of charged domain walls, which should be very useful for the fabrication of domain wall devices. The implication of such a shear-stress-modified polarization switching on the design of vortex memory device is also discussed.

近期，固体中挠曲电现象重新受到关注，这推动了有关通过机械载荷实现铁电畴翻转的研究。在这项工作中，我们结合热力学计算和相场模拟发现，在铁电体中，通过一种简单的机制，利用剪切应力就可以实现极化的机械翻转，而无需挠曲电的存在。这种翻转是剪切应力与位于剪切应变平面内的两个极化分量之间的三线性耦合的结果。具体而言，当一个极化分量的方向固定时，施加剪切应力可以诱导另一个极化分量的翻转。此外，当剪切应力固定时，一个极化分量的翻转会导致另一个极化分量的翻转。我们计算了稳定极化状态随剪切应力、温度和电场变化的相图。而且，正如对铁电薄膜进行的相场模拟所表明的那样，畴翻转确实可以通过局部剪切应力实现。重要的是，剪切应力和电场的共同作用可以实现带电畴壁的确定性写入，这对于畴壁器件的制造应该是非常有用的。我们还讨论了这种受剪切应力调控的极化翻转对涡旋存储器件设计的影响。