Structural, optical, and dielectric properties of LaFe_1−xMn_xO₃ (x = 0.00, 0.05, 0.10, 0.15, and 0.20) perovskites

Herein, we investigated the structural, optical, and dielectric properties of perovskite LaFe_1−xMn_xO₃ (x = 0.00, 0.05, 0.10, 0.15, and 0.20) polycrystalline ceramics synthesized using sol–gel and sintering methods. X-ray diffraction measurements revealed that these materials adopt a single-phase orthorhombic crystal structure (space group Pnma). The effects of the Mn substitution induce changes in the lattice parameters including the Fe/Mn–O–Fe/Mn bond angle, Fe/Mn–O bond length, and tilting of the bond angle; these changes are also supported by the tolerance factor calculations and Raman scattering analysis. The complex impedance of the samples was measured in the temperature range of 100 °C to 275 °C and over the frequency range of 100 Hz to 1 MHz. The Nyquist plots, i.e., Z″ versus Z′ over the entire frequency range, resembled semicircular arcs and could be described by an electrical equivalent circuit model. The complex conductivity of the samples was investigated using both the equivalent circuit modelling and the Jonscher universal power law. The activation energies of the conduction processes obtained from both methods were very similar, indicating that the model comprising discrete electrical components used to interpret the response of the real system is applicable. The activation energies from conduction and relaxation processes were found to be < 1 eV, indicating that the mechanisms might be predominantly induced by oxygen ionic conductivity rather than electronic conductivity and oxygen vacancies.