Dependence of electrical transport properties of CaO(CaMnO₃)_m (m = 1, 2, 3, ∞) thermoelectric oxides on lattice periodicity

The electrical transport properties of CaO(CaMnO₃)_m (m = 1, 2, 3, ∞) compounds are studied applying the density functional theory (DFT) in terms of band structure at the vicinity of the Fermi level (E_F). It is shown that the total density of states (DOS) values at E_F increase with increase in the m-values, which implies an increase in the electrical conductivity, σ, with increasing m-values, in full accordance with experimental results. Additionally, the calculated values of the relative slopes of the DOS at E_F correlate with the experimentally measured Seebeck coefficients. The electrical conductivity and Seebeck coefficients were calculated in the framework of the Boltzmann transport theory applying the constant relaxation time approximation. By the analysis of experimental and calculated σ(Τ) dependences, the electronic relaxation time and mean free path values were estimated. It is shown that the electrical transport is dominated by electron scattering on the boundaries between perovskite (CaMnO₃) and Ca oxide (CaO) layers inside the crystal lattice.