NSF-BSF: Electrostriction in Ceramic Materials with Dynamic Elastic Dipoles

非技术性总结：电致伸缩器将电能转换为机械能，但不能将机械能转换为电能。这种机电转换的结构基础与压电材料根本不同，压电材料能够实现电能到机械能的转换，反之亦然。NCES效应是最近由主要研究者A. Frenkel（斯托尼布鲁克大学，美国）和国外合作者（FC），I. Lubomirsky（Weizmann Institute，Israel）在Zr掺杂的氧化铈中，响应于所施加的电场，比在经典电致伸缩器中预测的变形大得多（两个或更多个数量级）。具体地说，虽然目前商业上使用的电致伸缩器是铅基的，但新发现的组合物是完全无毒的。与之前报道的NCES相比，新发现的材料没有局部弹性偶极子，这是晶胞内的永久扭曲，破坏了整体对称性。相反，新发现的材料中的扭曲是动态的，清楚地表明NCES以前未知的机制正在起作用。该团队将研究这类材料（Zr和Hf掺杂的二氧化铈）中电致伸缩的起源，采用先进的时间分辨技术，基于PI执行的同步加速器X射线吸收光谱，以及FC执行的机电测量，FC也将合成样品。该项目将利用美国PI的专业知识，在使用功能材料的先进原子和结构表征方面，与以色列合作者的专业知识，在陶瓷的制备和机械性能方面。该团队将对Zr（Hf）和Ce原子的局部环境进行原子级表征，有和没有电场，通过时间分辨方法检测偶极子对电场变化的动态响应。该项目将取得四项重要成果：（1）获得具有动态弹性偶极子的NCES的基本描述符，（2）为NCES效应的理论建模提供基础，（3）培训新一代专门从事材料科学的研究生和本科生，使其掌握在大型用户设施中实践的先进表征方法，（4）建立一个国际合作项目框架，将斯托尼布鲁克大学和魏茨曼科学研究所的师生研究团队联系起来。Frenkel（斯托尼布鲁克大学，美国）和国外合作者（FC），I. Lubomirsky（以色列魏茨曼研究所），导致了非经典电致伸缩效应（NCES）的发现。这些材料的电致伸缩系数比经典标度定律预测的高两个或更多个数量级，并且与先前在离子导体中观察到的相似。NCES最初在非常低的频率下被检测到，产生非常小的变形（几ppm），并且归因于由点缺陷、氧空位或质子空穴引起的弹性偶极子。PI和FC的团队最近发现了一种材料，Zr掺杂的氧化铈，它在所有实际参数上都表现出NCES与商业使用的电致伸缩器相媲美：数百ppm的应变，大弹性模量和kHz范围响应。因此，除了新组合物完全无毒的突出优点之外，这些性质还有望取代商业铅基电致伸缩器。这种材料不含有大量的空位或杂质，因此不具有永久弹性偶极子，这清楚地表明NCES的一种以前未知的机制正在起作用。该项目将利用美国首席研究员在使用功能材料的先进原子和结构表征方面的专业知识，以及以色列合作者在陶瓷制备和机械性能方面的专业知识。该项目的最终目标是在存在和不存在外部施加电场的情况下，对NCES的局部离子环境进行原子级表征。时间分辨的同步辐射表征方法是唯一有吸引力的，因为它们捕获的化学键的元素特定的变化。该项目将取得四项重要成果：（1）获得具有动态弹性偶极子的NCES的基本描述符，（2）为NCES效应的理论建模提供基础，（3）培训新一代专门从事材料科学的研究生和本科生，使其掌握在大型用户设施中实践的先进表征方法，（4）建立国际合作项目框架，该奖项反映了NSF的法定使命，并通过使用基金会的知识产权进行评估，被认为值得支持。优点和更广泛的影响审查标准。

NON-TECHNICAL SUMMARY: Electrostrictors convert electrical energy into mechanical energy but not vice versa. The structural basis for this electromechanical transduction is fundamentally different from piezoelectric materials, which enabled electrical to mechanical energy conversion and vice versa. The NCES effect, recently discovered by the principal investigator (PI), A. Frenkel (Stony Brook University, USA) and the foreign collaborator (FC), I. Lubomirsky (Weizmann Institute, Israel) in Zr-doped cerium oxide, results in much larger (by two or more orders of magnitude) deformation in response to an applied electric field than that predicted in classical electrostrictors. Specifically, while current commercially used electrostrictors are lead-based, the newly discovered compositions are completely nontoxic. In contrast, to the previously reported cases of NCES, the newly discovered materials do not have local elastic dipoles which are permanent distortions within the unit cells, breaking the overall symmetry. Instead, the distortions in the newly discovered materials are dynamic, clearly indicating that the previously unknown mechanism of NCES is at work. The team will investigate the origin of the electrostriction in this class of materials (Zr- and Hf- doped ceria) with advanced time-resolved techniques based on synchrotron X-ray absorption spectroscopy, performed by the PI, and electromechanical measurements, performed by the FC who will also synthesize the samples. This project will leverage the expertise of the US PI, in using advance atomistic and structural characterization of functional materials, with the expertise of the Israeli collaborator, in preparation and mechanical properties of ceramics. The team will perform atomic-level characterization of the local environment of Zr (Hf) and Ce atoms, with and without electric field, through time-resolved methods for detecting the dynamic response of the dipoles to the changing electric field. The project will have four important outcomes: (1) Obtaining the fundamental descriptors of NCES with dynamics elastic dipoles, (2) Providing basis for the theoretical modeling of the NCES effect, (3) Training a new generation of graduate and undergraduate students specializing in materials science on advanced characterization methods practiced at large user facilities, and (4) Establishing a framework of collaborative international projects connecting faculty-student research teams of Stony Brook University and Weizmann Institute of Science.TECHNICAL SUMMARY: During the last decade, the collaboration of the principal investigator (PI), A. Frenkel (Stony Brook University, USA) and the foreign collaborator (FC), I. Lubomirsky (Weizmann Institute, Israel), has led to the discovery of the non-classical electrostriction effect (NCES). These materials show an electrostrictive coefficient two or more orders of magnitude higher than predicted by the classical scaling law and similar to what previously observed exclusively in ionic conductors. NCES was originally detected at very low frequencies, produced very small deformation (few ppm), and was attributed to the elastic dipoles induced by point defects, oxygen vacancies or proton interstitials. The team of the PI and FC has recently discovered a material, Zr-doped cerium oxide, that exhibits NCES rivaling commercially used electrostrictors in all practical parameters: hundreds of ppm of strain, large elastic modulus, and kHz-range response. Therefore, such properties, in addition to the prominent advantage of the new composition to be completely nontoxic, promise a replacement of the commercial lead-based electrostrictors. This material does not contain significant concentration of vacancies or interstitials and, thereby, does not have permanent elastic dipoles, clearly indicating that a previously unknown mechanism of NCES is at work. This project will leverage the expertise of the US Principal Investigator in using advance atomistic and structural characterization of functional materials, with the expertise of the Israeli collaborator in preparation and mechanical properties of ceramics. The ultimate goal of the project is atomic-level characterization of the local ionic environment of the NCES, in presence and absence of an external applied electric field. Time-resolved methods of synchrotron characterization are uniquely attractive for this purpose because they capture the element-specific changes in the chemical bons. The project will have four important outcomes: (1) Obtaining the fundamental descriptors of NCES with dynamics elastic dipoles, (2) Providing basis for the theoretical modeling of the NCES effect, (3) Training a new generation of graduate and undergraduate students specializing in materials science on advanced characterization methods practiced at large user facilities, and (4) Establishing a framework of collaborative international projects connecting faculty-student research teams of Stony Brook University and Weizmann Institute of Science.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.