DC Conductivity of Ca1-xNaxMnO3 Perovskites.

DC conductivity of electron doped antiferromagnetic Ca1-xNaxMnO3 (0 ≤ x ≤ 0.3) perovskites has been studied elaborately. Na doping initially increases the dc conductivity and decreases the activation energy of CaMnO3. Above 5% doping, it starts decreasing the conductivity. The Debye temperature (θD) also decreases from 419 to 322 K with the increase of x. The dc conduction in undoped sample takes place by small polaron hopping (SPH) conduction in the non-adiabatic regime. There may be a tendency of large polaron formation in 10-30% Na doped samples due to larger ionic radius of Na1+ compared to that of Mn4+ and Ca2+. Strong e-ph interaction is observed in undoped sample followed by a weaker interaction with the increase of Na concentration. Mott's variable range hopping (VRH) model can explain the dc conductivity at very low temperatures (T < θD/4). It has been detected that single-phonon assisted hopping is responsible for the dc conduction in the Na doped CaMnO3 manganites. [ABSTRACT FROM AUTHOR]