KY EPSCoR: Designing "Phonon-Glass" Mixed Oxide Nanocomposites for Thermoelectric Energy Conversion

Thermoelectric (TE) devices convert heat to electrical energy and vice-versa, and have wide application as thermal controls and energy generation devices in both current and future NASA technologies. Existing TE materials with high energy-conversion efficiencies (as represented by large TE figures-of-merit) are either unsuitable for use at high temperatures or in oxidizing environments, or are synthesized using rare or expensive elements (e.g., Te). Recent studies have indicated that alloys of abundant metal oxide precursors (e.g., (Ba,Sr)TiO3 and FeCoMnO3) form self-assembled nanocomposite materials consisting of two compositionally and/or structurally distinct domains with characteristic domain sizes on the nanoscale. These nanocomposite materials have been shown to strongly scatter phonons while exhibiting limited electron scattering. Low thermal conductivity due to high phonon scattering, but also high electrical conductivity due to low electron scattering (“phonon-glass” behavior) are precisely the materials properties required to maximize the TE figure-of-merit. Hence, previous and preliminary results suggest the possibility of designing optimized “phonon-glass” mixed oxide materials exhibiting high TE figures-of-merit, high stability at temperature and/or in oxidizing environments, and requiring only abundant, low-cost precursor materials. This proposed project seeks to initiate an integrated computational and experimental research program to (i) understand the processing–structure–properties relationships governing thermoelectric (TE) properties in self-assembling mixed oxide nanocomposite (NC) materials, and (ii) leverage this understanding via improved theoretical models to design and fabricate new NC materials with high TE figures of merit, low synthesis costs, and high stability at temperature and in oxidizing environments.