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

Perovskite-type oxides LaCaFeO (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 due to asymmetric stretching of the octahedron. The reflectance spectra showed characteristic d→ d transitions arising from the Fe 3d and the highest optical band gap energy (E) of 2.57 eV was exhibited by LaFeO, while the lowest E (1.41 eV) was shown by LaCaFeO 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 (Pm3 ¯ m) was found when x was increased from 0.4 to 0.6. TGA showed that LaFeO was the most stable with a residual mass of ~ 97 wt% at 900 C compared to CaFeO (~ 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 substitution, tan δ at 20 Hz significantly reduced from ~ 10 for x = 0 to ~ 10 for x = 1.0. The high polarization observed was due to e hopping between Fe↔ Fe. 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.