Investigation of electron and phonon transport in Bi-doped CaMnO3 for thermoelectric applications

The electron and phonon transports in CaMnO3 and in one of its Bi-doped counterparts, namely, Bi0.03Ca0.97MnO3, are investigated using the thermoelectric transport measurements and first-principles calculations. We find that antiferromagnetic insulator CaMnO3 breaks the Wiedemann-Franz law with the Lorenz number reaching four times that of ordinary metals at room temperature. Bismuth doping reduces both the electrical resistivity and Seebeck coefficient of CaMnO3; thus, it recovers the Wiedemann-Franz law behavior. In addition, Bi0.03Ca0.97MnO3 possesses a shorter phonon lifetime according to the transport measurements. As a result, Bi0.03Ca0.97MnO3 exhibits superior thermoelectric properties over pristine CaMnO3 owing to the lower thermal conductivity and electrical resistivity.