Novel phase change materials with tunable transition properties

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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.