Ferroelectric materials are characterized by the presence of an electric dipole that can be reversed by application of an external electric field, a feature that is exploited in ferroelectric memories. All ferroelectrics are piezoelectric, and therefore exhibit a strong intrinsic coupling between polarization and elastic deformation - a feature widely used in piezoelectric transducers and high-displacement actuators. A less explored and exploited property is flexoelectricity, i.e. the coupling between polarization and a strain gradient. Though flexoelectricity is an old concept (it was discovered in the Soviet Union almost 50 years ago), it is only with the advent of nanotechnology that its full potential is beginning to be realized, as gradients at the nanoscale can be much larger than at the macroscopic scale. Here, we demonstrate that the stress gradient generated by the tip of an atomic force microscope can be used to mechanically switch the polarization in the nanoscale volume of a ferroelectric film. This observation shows that pure mechanical force can be used as a dynamic tool for polarization control, enabling information processing in a new type of multiferroic high-density data storage devices where the memory bits are written mechanically and read electrically.
Electric-field-tunable mechanical properties of relaxor ferroelectric single crystal measured by nanoindentation
采用纳米压痕技术研究了弛豫铁电材料Pb（Mn 1/3 Nb 2/3）O3-PbTiO 3的电场效应.报道了巨电场可调的表观弹性模量（高达-39%）、硬度（-9%至20%）和能量耗散（高达-13%）。基于实验数据，提出了一种机电耦合纳米压痕的表征方法。该方法可以确定铁电材料弹性模量、硬度和压痕功之间的电场可调标度关系。此外，该方法还可以得到与电场相关的弹性模量和硬度，避免了Oliver-Pharr方法中接触面积的估算。最后，正、负电场对弹性模量的不同影响可以用挠曲电效应来解释。
Max Planck Institute for the Physics of Complex Systems（马克斯·普朗克复杂系统物理研究所）；Institute of Physics, Czech Academy of Sciences（捷克科学院物理研究所）；Institut für Physik, Johannes Gutenberg Universität Mainz（约翰内斯·古腾堡美因茨大学物理系）；Department of Physics, Massachusetts Institute of Technology（麻省理工学院物理系）；Max Planck Institute for Chemical Physics of Solids（马克斯·普朗克固体化学物理研究所）
Origin and Reduction of Coercive Fields in ZnO-based Wurtzite Ferroelectrics
Bredesen Center for Interdisciplinary Research, University of Tennessee（田纳西大学布雷德森跨学科研究中心）；Center for Nanophase Materials Sciences, Oak Ridge National Laboratory（橡树岭国家实验室纳米材料科学中心）；Department of Mechanical Engineering, The Pennsylvania State University（宾夕法尼亚州立大学机械工程系）；Department of Materials Science and Engineering, The Pennsylvania State University（宾夕法尼亚州立大学材料科学与工程系）
