Defects and electrical properties in Bi-doped calcium manganite

The air synthesized samples Ca 1– x Bi x MnO 3– δ , where x = 0.05, 0.10 and 0.15, show the formation of fully oxidized solid solution, δ = 0, with the orthorhombic structure (S G Pnma ). It is shown that electrical properties at temperatures below 700 K are mostly governed by the charge disproportionation and local Jahn–Teller distortions of octahedral oxygen environment of Mn 3+ cations. The bismuth doping strongly affects the disproportionation enthalpy, charge carriers concentration and conductivity. The metallic-like temperature dependencies of electrical conductivity and thermopower are interpreted within frameworks of a small polaron mechanism of electron transport. The maximum power factor 250 μ W·K –2 ·m –1 is observed in Ca 0.85 Bi 0.15 MnO 3– δ at 1120 K.