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.