Interface Structure and Dynamics in Multiferroic Phase Transformations

多铁相变中的界面结构和动力学

• 批准号: 1609545
• 负责人: Paul Evans
• 金额: $ 50.15万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-07-01 至 2021-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1609545&HistoricalAwards=false
• 关键词: Interface; Structure; Dynamics; Multiferroic; Phase

NON-TECHNICAL DESCRIPTION: The functional properties of emerging electronic ceramics based on structurally and chemically complex metal oxides depend very strongly on the crystal structures of these compounds. A series of recently discovered materials have competing stable phases with different crystallographic structures and can be reproducibly and rapidly transformed between phases. These structural phases differ significantly in their properties; new functionality in electronic and optical devices is enabled by switching between phases. At present, the detailed structural mechanism of these phase transformations, including the motion of the boundaries between phases, is not clear. This project comprises a series of experimental studies designed to probe the dynamics of this phase transformation, to answer key questions about the physical mechanism involved, and ultimately to provide feedback to the design of improved electroceramics.TECHNICAL DETAILS: The single-phase complex oxide bismuth ferrite, a prototypical multiferroic complex oxide, can be reproducibly transformed between structural phases with different symmetries, optical properties, and magnetic structures. Prof. Evans focuses on this model system because bismuth ferrite can be reliably synthesized using epitaxial growth techniques (e.g., ion sputtering, pulsed laser deposition, and chemical vapor deposition) such that it is near a phase boundary where phase transitions can be utilized in electromechanical, optoelectronic, and magnetic devices. Evans's initial results show that bismuth ferrite can be reproducibly transformed between structural phases on timescales as short as tens of nanoseconds, but these studies do not have sufficient time resolution to probe the fundamental timescale of the transformation. Through this project, Evans will (1) determine the short-time dynamics of rhombohedral behaviour (R-like) and tetragonal behaviour (T-like) phase populations in bismuth ferrite using picosecond-scale optical excitation and few-nanosecond-resolution electric field pulses, (2) probe the strain distribution and structure of individual R-like/T-like phase interfaces using X-ray nanobeam diffraction, (3) study the structure and dynamics of individual R-like/T-like interfaces in applied electric fields to determine the difference in dynamics arising from differing interface structures, and (4) explore the extension of these concepts to the interface dynamics in related phase-transforming complex oxides. Evans's work uses emerging synchrotron X-ray nanodiffraction methods, including recent advances in the analysis of diffraction patterns acquired with highly convergent coherent X-ray beams. This project supports the professional preparation of graduate students, participation of undergraduate students in research, targeted outreach through the development and demonstration of educational activities, and the dissemination of materials characterization and X-ray nanobeam diffraction methods to the broader research community.

非技术描述：基于结构和化学复杂的金属氧化物的新兴电子陶瓷的功能特性非常强烈地依赖于这些化合物的晶体结构。最近发现的一系列材料具有不同晶体结构的竞争稳定相，并且可以在相之间重复和快速地转变。这些结构相在其性质上显著不同;电子和光学器件中的新功能通过在相之间切换而实现。目前，这些相变的详细结构机制，包括相之间边界的运动，还不清楚。该项目包括一系列实验研究，旨在探索这种相变的动力学，回答有关所涉及的物理机制的关键问题，并最终为改进电瓷的设计提供反馈。技术参数：单相复合氧化物铁酸铋是一种典型的多铁性复合氧化物，可以在具有不同对称性、光学性质磁性结构。埃文斯教授专注于这个模型系统，因为铁酸铋可以使用外延生长技术可靠地合成（例如，离子溅射、脉冲激光沉积和化学气相沉积），使得其接近相变可用于机电、光电和磁器件的相边界。埃文斯的初步结果表明，铁酸铋可以在几十纳秒的时间尺度上在结构相之间重复转变，但这些研究没有足够的时间分辨率来探测转变的基本时间尺度。通过这个项目，埃文斯将（1）使用皮秒级光激发和几纳秒分辨率的电场脉冲确定铁酸铋中菱面体行为（R-样）和四面体行为（T-样）相群体的短期动力学，（2）使用X射线纳米束衍射探测单个R-样/T-样相界面的应变分布和结构，（3）研究在外加电场中单个类R/类T界面的结构和动力学，以确定由不同界面结构引起的动力学差异，以及（4）探索这些概念在相关相变复合氧化物中的界面动力学的扩展。Evans的工作使用了新兴的同步加速器X射线纳米衍射方法，包括高度会聚的相干X射线束获得的衍射图案分析的最新进展。该项目支持研究生的专业准备，本科生参与研究，通过开发和展示教育活动进行有针对性的推广，以及向更广泛的研究界传播材料表征和X射线纳米束衍射方法。