Enhanced dielectric and charge transport behavior in La1-xBixFeO3 ceramics: role of low-level Bi substitution

Abstract

The structural and dielectric properties of La1-xBixFeO3 ceramics (x = 0, 0.025, 0.05, 0.10, 0.15), synthesized via the sol–gel method, were investigated to assess their potential for electronic applications. X-ray diffraction (XRD) and Rietveld refinement confirmed a single-phase orthorhombic structure (Pbnm), with an increase in crystallite size from 32.25 to 55.58 nm and minimal lattice distortion due to the comparable ionic radii of Bi3+ and La3+. Raman spectroscopy revealed shifts and broadening in low-frequency Ag modes ( <200 cm–1), indicating enhanced structural disorder attributed to the distinct electronic configuration of Bi3+. SEM observations revealed that Bi substitution promotes grain growth, evolving from highly agglomerated particles in the undoped sample to well-developed micrometer-scale grains for x ≥ 0.05. EDX analysis confirmed the expected elemental composition and effective Bi incorporation into the lattice. Dielectric measurements over the 10 Hz–1 MHz frequency and 40–120 °C temperature ranges showed improved performance with Bi substitution. Nyquist plots displayed semicircular arcs associated with grain and grain boundary effects. Impedance analysis confirmed thermally activated conduction, while electric modulus (M″) spectra revealed non-Debye relaxation with grain boundary contributions. The activation energy for grain boundary relaxation decreased from 0.44 eV (x = 0) to 0.34 eV (x = 0.05), then increased at higher doping levels. The dielectric constant nearly doubled at x = 0.05, attributed to reduced relaxation energy and enhanced interfacial polarization. AC conductivity followed a similar trend, peaking at x = 0.05. The temperature-dependent frequency exponent (s) confirmed that the conduction mechanism follows the correlated barrier hopping (CBH) model. Additionally, the density of localized states (NT) and hopping distance (Rω) were analyzed as functions of frequency and temperature, providing further insights into charge transport dynamics. La0.95Bi0.05FeO3 exhibited optimal dielectric and transport behavior, demonstrating the potential of low-level Bi substitution for electronic applications.