Structural, optical, and impedance spectroscopy of the pseudobrookite Pb0·5Ba0·5Fe2O5 synthesized by sol–gel route

Abstract

Pseudobrookite of general formula Pb0·5Ba0·5Fe2O5 was synthesized by the sol–gel route. X-ray diffraction confirms the orthorhombic Pnma space group of our sample. UV–Vis absorption spectroscopy was used to characterize this material's optical properties. We used the Tauc model and absorption measurements to estimate the direct optical band gap at 3.53 eV. We also calculate the Urbach energy, the optical extinction coefficient, and the refractive index. In addition, the skin depth, optical conductivity, and Cauchy parameters were investigated in relation to the incident photon's wavelength. Electrical conductivity data flow the Jonscher's power law and show that PBFO has two different conducts; Semiconductor behavior in the temperatures region [400 K–520 K]. Then, a metallic trend was detected beyond TS-M = 520 K. The correlated barrier hopping (CBH) model is the appropriate model to describe the conduction process in low temperature range. On the other hand, the conduction is ensured by the non-overlapping small polaron tunneling (NSPT) at high temperature zone. The scaling study shows that the conductivity spectra deviate from Summerfield and Ghosh scaling. The random barrier model (RBM) is employed to correct the Summerfield approach and we note that the conductivity isotherms are combined into a single master curve. The estimated activation energies values from dc-conductivity, hopping frequency and relaxation time are very close. The behavior of dielectric parameters was examined using the Maxwell-Wagner theory of interfacial polarization. The dielectric-relaxation phenomenon is shown by the behaviors of imaginary parts of impedance (Z″) and modulus (M″). The ideal electrical equivalent circuit for simulating the Nyquist curves (i.e. Z′′(Z′)) for our pseudobrookite is (Rg + Rgb//CPEgb). Finally, the entropy (ΔS), and enthalpy (ΔH) were established as thermodynamic parameters.