Adiabatic small polaron-hopping conduction in Ln0.85Ca0.15MnO3 (Ln=Nd, Pr and Sm) perovskites

Polycrystalline bulk ferromagnetic insulating (FMI) Ln0.85Ca0.15MnO3 (Ln=Nd, Pr and Sm) samples are prepared by standard solid-state reaction route and characterized. Powder X-ray diffraction (XRD) data of the manganites show single-phase character. Existing theoretical models predict that the high temperature (T>θD/2, θD being the Debye temperature) dc conductivity (σdc) of these samples is due to adiabatic small polaron-hopping conduction. Greaves’ and Mott's variable range hopping (VRH) conduction mechanisms are not suitable to explain the σdc data at low temperature (T<θD/2).