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Wednesday, February 27

Molecular Level Assessment of Thermoelectricity and Thermal Transport

Alper Kinaci, Texas A&M University, College Station, TX
Materials Science & Technology Division Seminar
11:00 AM — 12:00 PM, High Temperature Materials Laboratory (HTML), Building 4515, Room 265
Contact: Olivier Delaire (delaireoa@ornl.gov), 865.576.4644

Abstract

The ability to manipulate material response to dynamical processes depends on the extent of understanding of transport properties and their variation with chemical and structural features in materials. In this perspective, current work focuses on the electronic transport in bulk strontium titanate (SrTiO3) and thermal transport in carbon- and boron nitride-based nanomaterials.

Strontium titanate is highly recognized as a potential thermoelectric material for its large Seebeck coefficient. Here, first principles electronic band structure and Boltzmann transport calculations are employed in studying the thermoelectric properties of this material in doped and deformed states. The calculations verified that excessive carrier concentrations are needed for this material to be used in thermoelectric applications. It is also shown that rigid band approximation is applicable for La and Nb substitutions for a wide range of doping concentrations in this system.

Carbon- and boron nitride-based nanostructures offer new opportunities in many applications from thermoelectrics to fast heat removers. In this study, the influences of the structural details (size, dimensionality) and defects (vacancies, Stone-Wales defects, edge roughness, isotopic disorder) on the thermal conductivity of C and BN nanostructures are explored. In pristine states, BN nanostructures have 4-6 times lower thermal conductivity compared to C counterparts. The reason of this observation is investigated on the basis of phonon group velocities, life times, heat capacities and corresponding quantum corrections to these variables. The calculations show that both phonon group velocities and life times are smaller in BN systems. The chemical and structural diversity that could be attained by mixing hexagonal boron nitride and graphene provides further avenues for tuning thermal and electronic properties. In this respect, the thermal conductivities of hybrid graphene/hexagonal-BN structures are also studied. The largest reduction in thermal conductivity is observed at 50% chemical mixture in dot superlattices. The dot radius appears to have little effect on the magnitude of reduction around this composition while smaller dots are more influential at dilute systems.