Dielectric relaxation and variable range hopping conduction in sol-gel auto combustion derived La0.7Bi0.3Fe0.5Mn0.5O3 manganite

Highlights: • Polycrystalline La_0.7Bi_0.3Fe_0.5Mn_0.5O₃ manganite was prepared via sol-gel auto-combustion route. • The FESEM revealed grains and grain boundaries as micro-constituents of the sample. • The effect of bulk and interface parts on the transport mechanism was investigated by Impedance and Modulus and Spectra. • The Mott Variable Range Hopping was identified as the dominant conduction mechanism in the material. • Dielectric constant and loss factor exhibited relaxation with dispersion at high frequency. In the present work, the polycrystalline La_0.7Bi_0.3Fe_0.5Mn_0.5O₃ maganite was synthesized by sol-gel auto-combustion method. The room temperature X-ray powder diffraction pattern confirmed the orthorhombic phase of the sample with pbnm space group. Frequency and temperature dependent electric modulus and impedance spectroscopic analyses revealed two electro-active components of the material characterized by highly resistive grain boundaries and comparatively conducting grains, respectively. The normalized scaling behavior of modulus plots divulged the temperature independence of the dynamic process in electro-active regions. The fitting of impedance data by the equivalent circuit (R_G||Q_G) + (R_GB||Q_GB) was applied to explore the physical parameters associated with grains and grain boundaries. The dispersion in dielectric permittivity and loss factor at lower frequencies attributed to the space charge polarization were observed. The electrical conductivity obeyed Mott's T^1/4 law and the slope of frequency dependent AC conductivity spectra changed due to multiple activation barriers and active traps, consistent with the variable-range hopping conduction in the material.