Non-adiabatic polaron hopping conduction in CaMn1− x Cr x O3 (0⩽x⩽0.3)

Abstract: DC electrical conductivity (σ dc) of electron-doped antiferromagnetic CaMn1− x Cr x O3 (0⩽x⩽0.3) has been discussed elaborately in the light of polaron hopping conduction. The increase in Cr doping concentration increases the conductivity and decreases the activation energy. Non-adiabatic polaron hopping conduction is observed in all the manganites at high temperatures. The analysis of σ dc data shows that small polarons are formed at lower concentrations (⩽5%) of Cr doping and undoped samples. However, large polarons are materialized at higher doping (⩾10%) concentrations. This is consistent with the fact that doped Cr3+ has larger ionic size compared to that of Mn4+. Again, strong electron–phonon (e–ph) interaction is perceived in undoped and 5% Cr-doped samples but not in manganites with larger doping concentration. This also confirms the formation of larger polarons with the increase of x. Mott''s variable range hopping (VRH) model can elucidate the dc conductivity at very low temperatures. It has been detected that single phonon-assisted hopping is responsible for the dc conduction in the Cr-doped CaMnO3 manganites. [Copyright &y& Elsevier]