La0.67Pb0.33-xKxMnO3 perovskites synthesized by sol-gel method: the effect of potassium substitution on the magnetic and electrical properties

The influence of the potassium substitution for Pb ions in the mixed valence perovskites La0.67Pb0.33-xKxMnO3 (0 <= x <= 0.15) was investigated by X-ray diffraction, magnetic and electric transport measurements. All the compositions were synthesized using the sol-gel technique. X-ray diffraction and structure refinement showed that they crystallize in the rhombohedral structure with R (3) over barc space group. Upon K doping on Pb sites, the lattice parameters, unit cell volume, and the Mn-O-Mn bond angle were reduced. All the samples exhibited a ferromagnetic-paramagnetic transition and metallic-semiconductor one with increasing temperature. The analysis of the electrical resistivity data concluded that the metallic (ferromagnetic) part of the resistivity (below TM-Sc) can be explained by the following equation rho(T) = rho 0 + rho(2)-T-2 + rho T-4.5(4.5), signifying the importance of the domain boundary/grain, combination of electron-magnon, electronelectron and electron-phonon scattering processes. At higher-temperature (T > TM-Sc) paramagnetic semiconducting regime, the adiabatic small polarons hopping mechanism (ASPH) was found to fit well.