Polaronic transport properties in La1-xSrxFeO3 systems (0.05

Abstract

Electrical transports in the La1-xSrxFeO3 system (0.05<or=x<or=0.3) was investigated as a function of temperature from 80 K to 350 K by dielectric properties, DC and AC conductivities. Two dielectric relaxation peaks appeared and their relative peak heights were closely related to the amount of Sr. The intensities of both these peaks were thermally activated. In every specimen, there was an Arrhenius relation between sigma T and T, the activation energy of which was nearly equal to the sum of the activation energy required for the dielectric relaxation and that for the thermal activation in the intensity of the relaxation peak. The frequency dependences of AC conductivities obeyed an equation of sigma ( omega )=A omega 5 and AC conductivities were independent of temperature below approximately 200 K at every applied frequency. These results were explained self-consistently with small polarons of ligand holes (3d5L) which were transformed from the states of O 2p weight to the mixed Fe 3d-O 2p states with an increase in the covalent character as the amount of Sr increases, as confirmed by the soft-X-ray spectroscopies and XPS-experiments.