Electronic structure and thermal properties of doped CaMnO3 systems

The electronic and thermal properties of hole (Na) and electron (Ga) doped CaMnO3 systems are investigated based on the first principle density functional theory calculations using plane wave basis and pseudo-potential method. A semiconductor-to-conductor transition and a distorted band structure are found for the doped systems; enhanced density of states near Fermi level is observed. The phonon transfer speed and the phonon mean free path are lowered; meanwhile, the phonon specific heat is heightened in comparison with that of the undoped CaMnO3 system, resulting in enhanced phonon thermal conduction. The calculation results indicate that the doped systems should have improved thermoelectric performance.

Research highlights▶ A semiconductor-to-conductor transition is found in both of the hole and electron donor doped systems; energy for carriers to hop is reduced in the both doped systems. A distorted band structure is found within the doped systems, enhanced effective mass of carrier is observed. ▶ The density of states near Fermi level is enhanced. ▶ The phonon density of states, Debye temperature, phonon mean free path and phonon specific heat are calculated. The phonon transfer speed and phonon mean free path are lower, however the phonon specific heat is higher within the doped CaMnO3 system, resulting in enhanced phonon conduction within the doped CaMnO3 systems. ▶ As for thermoelectric property aspect, the thermopower, carrier conduction capability and thermal conduction are discussed at the end. The calculation results indicate the doped systems should have more promising thermoelectric performances.