First-principles design of strongly anharmonic crystalline solids with ultra-low lattice thermal conductivity

Yale University, New Haven CT

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports computational research and education to advance predictive modeling of thermal transport properties of insulating and semiconducting materials. Fossil fuels (petroleum, coal, and natural gas) account for the vast majority of the energy use in the world. Less than 1/3 of the total energy content is used productively, while the rest is rejected, mainly in the form of waste heat. In the US alone, the amount of this wasted energy is roughly equivalent to that contained in 400 billion gallons of gasoline. Many technologies for improving energy efficiency, or reusing the waste heat, depend on the availability of thermally insulating ceramics and semiconductors. For instance, thermoelectrics convert heat into electricity via a phenomenon called the Seebeck effect, which operates between a hot and a cold electrode. High-performance thermoelectric devices require materials that are poor conductors of heat but efficient conductors of electricity. Currently, few such materials are known, which prevents a wider adoption of this energy-saving technology. Similarly, better ceramic thermal insulators would save energy by enabling increased operating temperatures in combustion engines. Heat in nonmetallic crystals is conducted by atomic vibrations, such as sound waves. Conventional semiconductors (e.g. silicon) are poor thermal insulators because these waves propagate independently of each other and encounter little resistance. Empirical methods for decreasing thermal conductivity aim to impede the forward movement of vibrational waves. However, these approaches require complex preparation methods and are often limited in efficiency. The PI and his group will design materials that have intrinsically low thermal conductivity because the heat-carrying waves of atomic vibrations scatter off of each other. In select solids, this scattering can become so strong that the flow of heat reaches the lowest possible value associated with glasses and amorphous solids. The project will advance computational techniques and quantum mechanical concepts for identifying and deliberately creating thermally insulating solids with desired properties. The broader impacts of the proposed research are several-fold, involving broad dissemination of research results, education of graduate students in a rich multidisciplinary environment, and introduction of undergraduate students to modern computational methods. Successful completion of this research program will contribute to the development of new thermally insulating materials as thermoelectrics and coatings with potential benefits in energy conservation. The calculated thermal properties will be disseminated to the scientific and technical community by partnering with existing online databases of computed materials data. TECHNICAL SUMMARY This award supports research and education to advance predictive modeling of thermal transport properties of crystalline insulators and semiconductors via the development of computational methods and theoretical concepts for lowering lattice thermal conductivity. The PI and his group are mainly interested in strongly anharmonic solids where intrinsic phonon-phonon interactions limit thermal conductivity to values near the amorphous limit; such materials are of interest in energy conservation and waste-heat recovery as ceramic coatings and thermoelectrics. The PI's quantum-mechanics-based design strategy involves the use of lone-pair electrons that host anharmonic bonds, oxides, and oxosulfides of transition-metals that host strong p-d electronic hybridization effects, high-symmetry solids with ions near electronic Jahn-Teller instabilities, and compounds with frustrated structural coordination. These approaches are based on fundamental principles for enhancing intrinsic phonon scattering in crystalline materials via a mechanism that is independent of processing, impurities, and grain structure. This will allow the attainment of minimal lattice thermal conductivity in bulk oxides and semiconductors. To enable accurate computation of thermal properties, the group will pursue the following theoretical developments: (1) compressive-sensing-based methods for building lattice dynamical Hamiltonians for compositionally disordered materials, (2) efficient path integral molecular dynamics techniques for calculating low-temperature thermal transport properties of strongly anharmonic solids, and (3) electronic structure techniques for treating adiabatic lattice dynamics of solids with competing orbital ordering states in partially filled d-and f-electron shells. These methods will form a comprehensive suite of computational techniques for first-principles studies of thermal transport in anharmonic solids. The proposed work is expected to improve fundamental understanding of the thermal transport properties of strongly anharmonic materials, advance the theory and software tools for modeling thermal transport properties of solids, and provide a theoretical basis for rational design of materials with low thermal conductivity. The broader impacts of the proposed research are several-fold, involving broad dissemination of research results, education of graduate students in a rich multidisciplinary environment, and introduction of undergraduate students to modern computational methods. Successful completion of this research program will contribute to the development of new thermally insulating materials as thermoelectrics and coatings with potential benefits in energy conservation. The calculated thermal properties will be disseminated to the scientific and technical community by partnering with existing online databases of computed materials data.