Immobilization of Na ions for substantial power factor enhancement: site-specific defect engineering in Na0.8CoO2

Abstract

Simultaneous enhancement of the interdependent Seebeck coefficient and electrical conductivity has been achieved through defect engineering by doping Mg into specific sites of Na0.8CoO2. Results from thermoelectric measurement demonstrate that the power factor was substantially increased by 50% at ambient. Experimental and theoretical analyses show that the occupation of divalent Mg in the disordered Na layer immobilizes the Na ions and thus induces a long-range ordering of Na ions. This phenomenon improves the carrier mobility significantly, giving rise to the observed exotic thermoelectric performance. Moreover, it is predicted that other electronically closed-shell dopants in sodium cobaltate play a similar role in enhancing the thermoelectric conversion efficiency. © 2012, American Chemical Society.