Significant Enhancement in Thermoelectric Power Factor of Bulk Nanostructured Calcium Cobalt Oxide Ceramics

An elementary and economical approach is demonstrated for achieving bulk nanostructured calcium cobalt oxide (CCO) ceramics with enhanced thermoelectric power factor (PF) of 64.2 × 10–3 W m–1 K–2 at 770 K. Nanostructures of CCO are realized by high-energy ball-milling of the as-synthesized CCO and are consolidated using hot-press (HP) technique to form fully dense pellets. The morphological, crystallographic, and spectroscopic properties suggest the formation of highly pure nanostructures and ceramics of CCO. The significant improvement of ∼11 times in PF for bulk nanostructured CCO ceramics compared to the pellets of as-synthesized CCO microstructures is attributed to the enhancement of Seebeck coefficient (S) triggered due to structural deformations originated from the rearrangement of atomic contents and development of oxygen vacancies during the HP process of ceramic formation with application of high pressure at elevated temperatures and introduction of an enlarged interface area at grain boundaries in bulk nanostructuring. This concept of structural modulation triggered enhancement in S could be adopted for understanding the thermoelectric properties in other nanostructured materials, and the currently achieved bulk nanostructured CCO ceramics could be routinely utilized in developing efficient thermoelectric power generation devices for large-scale applications of converting the waste heat into a usable form of electrical energy.