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In this paper, an attempt was made to synthesize LaNiO3, CeNiO3, and BaNiO3, and Ce3+ and Ba2+ co-substituted LaNiO3. These samples were further subjected to various material characterization techniques in order to evaluate their physio-chemical properties. Scanning electron microscope (SEM) images showed large chunks of aggregated nanoparticles with minute voids. The EDX-derived atomic composition deviated from the nominal composition suggesting the occurrence of multiple phases. In addition, transmission electron microscope (TEM) images revealed that the samples exhibit uneven spherical shape with a high degree of aggregation. The Fourier transformed-infrared (FT-IR) spectra of the synthesized samples show vibrations of the BO6 octahedral indicating the presence of Ni–O bonds. In addition, metal-carboxyl vibrations were identified from the peaks at 1400 and 860 cm−1. Optical diffuse reflectance spectra (DRS) showed certain peaks originating from the O2− (2p) → Ni2+ (3d) charge transfer. The X-ray powder diffraction (XRPD) analysis revealed the existence of multiple phases for the samples CeNiO3, BaNiO3, and La(Ce, Ba)NiO3. Moreover, La(Ce, Ba)NiO3 contained four phases showing that the co-substitution of Ba2+ and Ce3+ into LaNiO3 may require more sophisticated methodologies. The sample BaNiO3 showed maximum weight loss, due to the existence of carbonate phase. The dielectric properties decreased with increasing frequency, while the ac electrical conductivity enhanced with increasing frequencies obeying the Maxwell–Wagner two-layer model in accordance with Koop's phenomenological theory. [ABSTRACT FROM AUTHOR]

Perovskite-type oxides La1-xCaxFeO3 (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 3d and the highest optical band gap energy ( E g ) of 2.57 eV was exhibited by LaFeO3, while the lowest E g (1.41 eV) was shown by La1-xCaxFeO3 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 LaFeO3 was the most stable with a residual mass of ~ 97 wt% at 900 ∘ C compared to CaFeO3 (~ 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 Ca2+ substitution, tan δ at 20 Hz significantly reduced from ~ 103 for x = 0 to ~ 100 for x = 1.0. The high polarization observed was due to e− hopping between Fe2+ ↔ Fe3+. 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. [ABSTRACT FROM AUTHOR]

This study addresses the effect of fuel-to-oxidizer ratio (∅ =1.47, 1.57, 1.67, 1.77 and 1.87) on the structural, optical and dielectric properties of iron oxide nanoparticles synthesized through solution-combustion technique with glycine as the fuel. The synthesized samples were characterized using scanning electron microscopy, energy dispersive X-ray (EDX) spectroscopy, Fourier transform-infrared spectroscopy (FT-IR), ultraviolet–visible (UV-VIS) diffuse reflectance spectroscopy (DRS), X-ray powder diffraction (XRPD) with Rietveld refinement, thermogravimetric analysis (TGA) and frequency-dependent dielectric analysis. Electron micrographs show no change in morphology with respect to ∅. The EDX results revealed the existence of Fe and O. FT-IR confirmed the metal-oxygen (M − O) functional groups of iron oxides typically present near ∼ 570 and ∼ 520 cm−1. The synthesized samples showed typical reflectance spectrum of iron oxides during UV–Vis DRS analysis, where the maximum optical band gap of 1.80 eV was displayed by Fe 2 O 3 with ∅ = 1.67. The diffraction peaks were indexed with two phases: α-Fe 2 O 3 and γ-Fe 2 O 3. It was observed that the γ -phase decreased as ∅ increased. Rietveld refinement showed that ∅ = 1.47 had γ-phase as the majority (96.46 wt%), while ∅ = 1.87 had α-phase as the majority (79.90 wt%). The average crystallite size of α-phase was found to be 44.72 nm, while that of the γ -phase was 27.53 nm. The real and imaginary parts of dielectric constant, dielectric tangent loss, electric modulus, impedance and ac conductivity with respect to varying frequency were studied. All the parameters display typical trends shown by Fe-based ceramics agreeing to the Maxwell-Wagner type of interfacial polarization. The modulus studies revealed that the samples show non-Debye type relaxations and it can be concluded that these materials are well suited for high-frequency applications. • Fe 2 O 3 was prepared by solution-combustion method with varying fuel-to-oxidizer ratio (1.47–1.87). • All the prepared samples have tetragonal and rhombohedral crystal structures. • The samples exhibited low dielectric loss and good stability over the frequency range studied. • AC electrical conductivity increased with increasing frequency. [ABSTRACT FROM AUTHOR]