Tweaking the interplay of the layers by substitution in Ca3Co4O9+δ for high efficiency thermoelectric materials

Abstract

Ca3Co4O9 is a well-known high temperature thermoelectric material owing to its sandwich type layered structure consisting of both conducting and insulating slabs. In the present study we attempt to enhance the electrical conductivity without affecting the thermal conductivity by suitable doping in these layers. Compositions with a general formula Ca3−xSrxCo4−xMgx/2Tix/2O9+δ (0 ≤ x ≤ 0.15) were prepared by conventional solid state method and subjected to routine characterization techniques like XRD, SEM and XPS. Sr substitution in the insulating layer and Mg, Ti substitution in the conductive layer led to a decrease in the electrical resistivity from 17.86 mΩ cm to 9.74 mΩ cm, which resulted in an increase in the power factors. The dimensionless thermoelectric figure of merit ZT is found to be 0.13 at 873 K for x = 0.15, which is ̴2.1 times higher than the parent compound attributed to the excess oxygen in the doped composition.