Thermoelectric Oxide Ceramics Outperforming Single Crystals Enabled by Dopant Segregations
Cesar-Octavio Romo-De-La-Cruz, Yun Chen, Liang Liang, Mark C. Williams, Xueyan Song
Abstract
Calcium cobaltite Ca3Co4O9+δ in a single-crystal form was reported with an extrapolated dimensionless thermoelectric figure of merit of 0.87 in the year 2003. Regardless of the intensive effort during the past 2 decades, the performance of polycrystalline ceramics remained low and was reported to be only ∼30 to 60% of that found for single crystals. Here, for the first time, the designed nonstoichiometric Ca3–xTbxCo4O9+δBiy ceramics with intragranular dopant substitution are introduced, where the undersized dopant of Tb depletes at the grain boundaries and the oversized Bi segregates at the grain boundaries. Such synergetic dopant distribution simultaneously increases the electrical conductivity and the Seebeck coefficient and results in the oxide ceramics with a peak ZT of 0.9, outperforming single crystals over a wide range of temperatures.