Collaborative Research: Martensitic Transformations in Paraelectric Shape Memory Ceramics Activated by an Electric Field

马氏体相变是发生在某些晶体材料中的结构变化，其中原子以协调的方式自发且快速地重新洗牌成新的晶体结构。在某些材料中，这种转变是可逆的，因此材料可以在两种形状之间来回反复转变，从而产生“形状记忆”的特性。在像氧化锆这样的马氏体陶瓷中，形状变化非常大（拉伸和收缩形状约10%），并且它也施加非常大的力。 因此，形状记忆材料就像“固态发动机”，能够像致动器一样对周围环境做功。更重要的是，最近已经发现，形状记忆氧化锆可以通过施加电场来转变，这为形状记忆的电子控制打开了大门。在材料研究部陶瓷计划的支持下，该项目研究了陶瓷中电形状记忆的新特性，并开发了发现和设计具有这种特性的新陶瓷材料的工具。该项目包括计算和理论努力，以了解不同参数如何影响马氏体相变，由杨百翰大学的荷马教授领导，以及验证晶体，温度和施加电场不同取向的相变理论的实验努力。这项合成和测试新的有前景的形状记忆陶瓷的研究是在马萨诸塞州理工学院的Schuh教授的研究小组中进行的。这项研究对致动器设备技术有影响，这些技术不像其他电子技术那样容易小型化。此外，该项目还将为两名博士生提供科学培训，每个机构一名，外展活动将涉及合作努力，以加强杨百翰大学材料科学辅修课程的推出，以统一校园内不同专业的材料导向学生。技术总结由材料研究部陶瓷项目支持，该项目研究了一类新的形状记忆陶瓷，其中形状记忆的经典优点（通过固态相变做大量机械功的能力）与激活该特性的新机制（电场驱动的顺电-顺电相变）配对。除了开发一种全新的“准电活性”陶瓷，可以执行有意义的机械工作和扩大电活性陶瓷的产品组合，该研究还对相变理论有更广泛的影响。本研究涉及四个相互关联的任务：（1）发展和验证热力学模型，该模型考虑了电-热-机械能对顺电-顺电马氏体相变的耦合影响;（2）研究晶体取向和各向异性材料性质对预测和观察到的相变条件的作用;（3）探索掺杂剂的作用以控制转变条件并使这种现象能够在室温下操作;（4）通过发现替代现象，扩大现象的物质范围（非氧化锆）形状记忆陶瓷，其表现出顺电-顺电马氏体转变。这些课题主要由马萨诸塞州理工学院的Schuh教授的研究小组和杨百翰大学的Homer教授的研究小组共同进行实验性研究。该奖项反映了NSF的法定使命，通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical SummaryA martensitic transformation is a structure change that takes place in some crystalline materials, in which the atoms spontaneously and rapidly reshuffle into a new crystal structure in a coordinated way. In some materials this transformation is reversible, so that the material can repeatedly transform back and forth between two shapes, giving rise to the property of “shape memory”. In a martensitic ceramic like zirconia, the shape change is very large (elongating and contracting a shape by ~10%) and it also exerts very large forces. For this reason, shape memory materials are like “solid-state engines”, able to do work on their surroundings as actuators. What is more, it has been recently discovered that shape memory zirconia can be transformed by applying electric fields to it, which opens the door to electronic control over shape memory. With support from the Ceramics Program in the Division of Materials Research, this project investigates the new property of electrical shape memory in ceramics and develops tools to discover and design new ceramic materials that exhibit this property. The project consists of computational and theoretical efforts to understand how different parameters affect the martensitic transformation, led by Prof. Homer at Brigham Young University, and an experimental effort to validate the phase transformation theory for different orientations of the crystals, temperatures, and applied electric fields. This research to synthesize and test new prospective shape memory ceramics is carried out in Prof. Schuh’s research group at the Massachusetts Institute of Technology. This research has implications for actuator device technologies, which have not been as easily miniaturized as other electronic technologies. Additionally, the project will also provide scientific training for two PhD students, one at each institution, and outreach activities will involve a collaborative effort to strengthen the roll out of a Materials Science minor program at BYU to unify materials-oriented students that are spread across different majors on campus.Technical SummarySupported by the Ceramics Program in the Division of Materials Research, this project investigates a new class of shape memory ceramics in which the classical advantages of shape memory (the ability to do large amounts of mechanical work through a solid state phase transformation) are paired with a new mechanism for activating that property (an electric field-driven paraelectric-to-paraelectric phase transformation). Besides developing an entirely new class of “paraelectroactive” ceramics that can perform meaningful mechanical work and expanding the portfolio of electroactive ceramics, the research also has implications for the theory of phase transformations more broadly. The research involves four interrelated tasks: (1) developing and validating thermodynamic models that incorporate the coupled influence of electrical-thermal-mechanical energy on a paraelectric-to-paraelectric martensitic transformation; (2) examining the role of crystal orientation and anisotropic material properties on the predicted and observed phase transformation conditions; (3) exploring the role of dopants to control the transformation conditions and enable room temperature operation of this phenomenon; (4) expanding the materials-scope of the phenomenon by discovering alternative (non-zirconia) shape memory ceramics that exhibit paraelectric-paraelectric martensitic transformations. These tasks are collaboratively investigated with a primarily experimental effort in Prof. Schuh’s research group at the Massachusetts Institute of Technology and Prof. Homer’s research group mostly carrying out theoretical effort at Brigham Young University.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.