Thermal Conductivity and Grain Boundary Energy of Interfaces in Multiphase Ceramics

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NON-TECHNICAL DESCRIPTION: The properties of many components can be improved by making composites containing more than one type of material. For example, stronger ceramics can be made by using a mixture of three different types of ceramics rather than just one. For technical applications where the transport of heat through a material is important, boundaries (interfaces), where the different types of ceramics touch, may block the flow of heat. This research studies how the interfaces between different types of ceramics change the flow of heat. The goal of this project is to help design better thermal insulation and better cooling systems, for improved energy efficiency and reduced cost. Graduate students and undergraduates will participate in this research, and high school students from low-income underrepresented backgrounds will spend each summer in the lab with engineering students and faculty as part of the pipeline program "Breakthrough to Engineering". TECHNICAL DETAILS: The goal of this project is to understand how interfaces between dissimilar ceramics affect the thermal conductivity of multiphase oxide materials. While the addition of discrete second and third phases can improve mechanical strength, enhance thermal conductivity, and increase thermal shock resistance in ceramics, recent reports suggest that the intrinsic thermal resistance (Kapitza resistance) of grain boundaries due to phonon scattering may limit thermal conductivity at small grain sizes. This research studies the grain size range below which the thermal conductivity is significantly decreased for multiphase oxide ceramics compared to single phase oxides, and evaluates the energy of interfaces and characterizes the chemical/structural disorder between phases to determine correlation with Kapitza resistances using polycrystalline materials and bicrystals. This research provides new insights into thermal transport in multiphase oxides based on the influence of the structure, chemistry, and relative energy of grain boundaries and interfaces. Computational modeling that includes grain boundary specific properties is used to better predict the thermal conductivity of multiphase oxide materials. The results of this research offer improved design strategies for applications of ceramics where thermal conductivity is paramount. Students are also trained on new thermal characterization methods such as the 3-omega technique, and new atomic resolution advanced transmission electron microscopy techniques.