Defects and electrical properties in Bi-doped calcium manganite

Abstract

The air synthesized samples Ca1-xBixMnO3-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 Mn3+ 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 μW•K-2•m-1 is observed in Ca0.85Bi0.15MnO3-δ at 1120 K.