Insights on the various structural, optical and dielectric characteristics of La1-xCaxFeO3 perovskite-type oxides synthesized through solution-combustion technique

Perovskite-type oxides La 1- x Ca x FeO 3 ( x = 0.0–1.0) were synthesized using combustion technique. The samples have been investigated using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy (DRS), X-ray powder diffraction (XRPD) using Rietveld refinement, thermogravimetric analysis (TGA) and dielectric spectroscopy. The SEM images showed spherical-shaped agglomerates having a non-uniform distribution of size. The EDX results suggested that the experimental chemical composition was in good accordance with the nominal values. FT-IR revealed multiple peaks in the range of 580–510 cm −1 due to asymmetric stretching of the octahedron. The reflectance spectra showed characteristic d → d transitions arising from the Fe 3 d and the highest optical band gap energy ( E g ) of 2.57 eV was exhibited by LaFeO 3 , while the lowest E g (1.41 eV) was shown by La 1- x Ca x FeO 3 with x = 0.6. The results suggest that these samples are suitable for photocatalytic applications. From phase evaluation of the diffraction patterns, it was found that five distinct phases exist in the series. A phase transformation from orthorhombic ( Pnma ) to cubic ( P m 3 ¯ m ) was found when x was increased from 0.4 to 0.6. TGA showed that LaFeO 3 was the most stable with a residual mass of ~ 97 wt% at 900 ∘ C compared to CaFeO 3 (~ 70 wt% at 900 ∘ C ). The evaluation of frequency-dependent (20 Hz–20 MHz) dielectric properties agreed with the Maxwell–Wagner two-layer model. After Ca 2+ substitution, tan δ at 20 Hz significantly reduced from ~ 10 3 for x = 0 to ~ 10 0 for x = 1.0. The high polarization observed was due to e − hopping between Fe 2+ ↔ Fe 3+ . The electrical models of the samples show non-Debye type relaxation behavior, while the ac conductivity enhanced with increasing frequency which was in accordance with Koop’s phenomenological theory.