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

非技术综述：电致伸缩器将电能转化为机械能，但反之亦然。这种机电转换的结构基础从根本上不同于压电材料，后者实现了电能到机械能量的相互转换。NCES效应是由首席研究员A.Frenkel(美国石溪大学)和国外合作者I.Luomirsky(以色列魏兹曼研究所)最近在掺锆氧化铈中发现的，它在外加电场的响应下产生了比经典电致伸缩器中预测的更大(两个或更多个数量级)的变形。具体地说，虽然目前商业上使用的电致伸缩器是基于铅的，但新发现的组合物完全无毒。相比之下，与之前报道的NCES案例相比，新发现的材料没有局部弹性偶极，这是单胞内的永久性扭曲，破坏了整体对称性。相反，新发现的材料中的扭曲是动态的，清楚地表明之前未知的NCES机制正在发挥作用。该团队将使用先进的时间分辨技术来调查这类材料(掺Zr和Hf的CeO2)的电致伸缩的来源，该技术基于同步辐射X射线吸收光谱，由PI执行，并由FC执行机电测量，FC也将合成样品。该项目将利用美国PI的专业知识，利用先进的原子学和功能材料的结构表征，以及以色列合作者的专业知识，在陶瓷的制备和机械性能方面。该团队将通过时间分辨方法检测偶极子对变化的电场的动态响应，在有电场和没有电场的情况下，对Zr(Hf)和Ce原子的局部环境进行原子水平的表征。该项目将有四个重要成果：(1)获得具有动力学弹性偶极子的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关于在大型用户设施中实践的先进表征方法，以及(4)建立一个连接石溪大学和魏茨曼科学研究所师生研究团队的合作国际项目框架。技术摘要：在过去的十年中，首席研究员(PI)、A.Frenkel(美国石溪大学)和外国合作者(FC)的合作，卢博米尔斯基(以色列魏兹曼研究所)发现了非经典电致伸缩效应(NCES)。这些材料的电致伸缩系数比经典标度定律预测的电致伸缩系数高两个数量级或更多，与以前在离子导体中观察到的相似。NCES最初是在很低的频率下检测到的，产生的变形很小(很少ppm)，并归因于由点缺陷、氧空位或质子间隙引起的弹性偶极子。PI和FC的团队最近发现了一种名为掺锆氧化铈的材料，它的NCES在所有实用参数上都可与商业使用的电致伸缩器相媲美：数百ppm的应变、大的弹性模数和khz范围响应。因此，这种性能，除了新组合物完全无毒的突出优势外，有望取代商用的铅基电致伸缩器。这种材料不包含大量的空位或间隙位，因此没有永久的弹性偶极子，这清楚地表明NCES的一种以前未知的机制正在发挥作用。该项目将利用美国首席调查员的专业知识，利用先进的原子学和功能材料的结构表征，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加电场的情况下，对NCES的当地离子环境进行原子水平的表征。时间分辨的同步加速器表征方法对于这一目的具有独特的吸引力，因为它们捕捉到了化学键中元素特定的变化。该项目将有四个重要成果：(1)获得具有动态弹性偶极子的NCES的基本描述，(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关于在大型用户设施中实践的先进表征方法，以及(4)建立一个连接石溪大学和魏茨曼科学研究所师生研究团队的合作国际项目框架。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.