Enhanced Thermoelectric Performance in Oxide Composites of La and Nb Codoped SrTiO3 by Using Graphite as the Electron Mobility Booster

Inherent insulating nature of oxides makes it challenging for use in thermoelectric applications that warrant reasonable electrical conductivity. In the present work, we have used graphite (G) to improve the electron transport in La_0.07Sr_0.93Ti_0.93Nb_0.07O₃ (LSTN) by making composites. Graphite acts as the electron momentum booster in the LSTN matrix, which otherwise suffers from Anderson localization of electrons, causing an order of magnitude increase in weighted mobility and electrical conductivity. As a result, the thermoelectric power factor increases more than 6 times due to graphite incorporation in LSTN. Furthermore, the lattice thermal conductivity is suppressed due to enhanced Umklapp scattering, as derived from the Debye-Callaway model. Hence, we have recorded ∼423% increment in the figure of merit (ZT) in LSTN + G composites. The maximum ZT obtained is 0.68 at 980 K for the LSTN with 1 wt % graphite composite. Furthermore, we have fabricated a four-legged n-type thermoelectric power generator demonstrating a milliwatt level power output, which hitherto remained unattainable for oxide thermoelectrics.