Novel phase change materials with tunable transition properties

非技术描述：氧化物基相变材料代表了一个有趣的材料家族，能够在相变过程中显著改变其物理性质。二氧化钒(VO2)作为其中的代表之一，因其在室温附近发生相变而备受关注。该项目试图通过一种新的两相纳米复合材料设计方法来调节相变特性(例如，相变温度)。通过在纳米复合薄膜中结合VO2和金属作为第二金属相，可以在很大范围内调节其相变性能。这种可调的转变特性对于包括热执行器、电开关设备和智能窗在内的各种应用至关重要。除了科学和技术的影响，这项研究还为研究生和本科生提供了相变材料、薄膜生长和材料表征等多学科研究领域的培训。研究成果通过与相变材料相关的课堂教学模块、本科生和高中生的暑期研究以及普渡妇女工程项目和Birck Nanoday Events赞助的各种外展活动来传播。技术描述：该项目专注于对新型两相金属-VO2纳米复合材料设计的基础材料探索，它们的相变特性，以及作为金属选择和纳米颗粒尺寸、密度和几何形状的函数的基本开关机制。作为Mott绝缘氧化物材料之一，VO2在68℃左右的加热过程中表现出从半导体相到金属相的超快可逆相变。为了使其能够实际应用，非常需要可调的相变特性(例如，在较宽的温度范围内调谐相变温度)。具体地说，该项目致力于以外延薄膜的形式合成两相金属-VO2纳米复合材料，通过选择金属来调节相变温度和相变性质，并通过剪裁两相形态来了解基本的相变机制，例如，金属相的几何形状、密度、尺寸等。相变性质是通过一套电传输和光学测量来测量的，并结合详细的微结构表征，包括高分辨率透射电子显微镜、原子尺度元素图谱和应变图谱。两相纳米复合材料的设计和对相变机理的基本理解可以应用于其他Mott绝缘氧化物系统，以实现VO2以外的可调相变性能。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 Description: Oxide-based phase change materials represent an interesting family of materials with ability to dramatically change their physical properties during phase transition processes. Vanadium dioxide (VO2), as one of the representatives, is of particular interest because of its phase transition could occur close to room temperature. The project seeks to tune the phase transition properties (e.g., phase transition temperature) through a novel two-phase nanocomposite design approach. By combining VO2 with a metal as a secondary metal phase in the nanocomposite thin films, the phase transition properties are tuned in a wide range. Such tunable transition properties are critical for various applications, including thermal actuators, electrical switching devices and smart windows. In addition to scientific and technological impacts, this research provides training to graduate and undergraduate students in the multidisciplinary research area of phase change materials, thin film growth and materials characterizations. The research findings are disseminated through in-class teaching modules related to phase change materials, summer research for undergraduates and high school students, and various outreach activities sponsored by Purdue Women in Engineering Program and Birck Nanoday events.Technical Description: The project focuses on a fundamental material exploration of novel two -phase metal-VO2 nanocomposite designs, their phase change properties and the fundamental switching mechanisms as functions of the metal selections and the nanoparticle dimensions, density and geometries. As one of the Mott insulating oxide materials, VO2 exhibits an ultrafast and reversible phase transition from a semiconductor phase to a metallic phase at about 68 ?C during heating process. To enable its practical applications, tunable transition properties (e.g., phase transition temperature tuning over a broad temperature range) are very much desired. Specifically, the project focuses on synthesizing the two-phase metal-VO2 nanocomposites in an epitaxial thin film form, tuning the transition temperature and phase transition properties via selection of metals, as well as understanding the fundamental phase transition mechanisms via tailoring the two-phase morphology, e.g., the metal phase geometry, density, dimension, etc. The phase change properties are measured by a set of electrical transport and optical measurements, coupled with a detailed microstructural characterization, including high resolution transmission electron microscopy, atomic scale elemental mapping and strain mapping. The two-phase nanocomposite design and the fundamental understanding on the phase transition mechanisms can be applied to other Mott insulating oxide systems for tunable phase change properties beyond VO2.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.