Formation Of LaFeO3 Research Articles

Structural, Vibrational, and Magnetic Characterization of Orthoferrite LaFeO3 Ceramic Prepared by Reaction Flash Sintering.

LaFeO3 perovskite ceramics have been prepared via reaction flash technique using Fe2O3 and La2O3 as precursors. The obtained pellets have been investigated using several techniques. The formation of LaFeO3 has been clearly confirmed by X-ray diffraction. The scanning electron microscopy micrographs have shown the microporous character of the obtained pellets due to the low temperature and dwell time used in the synthesis process (10 min at 1173 K). The orthorhombic-rhombohedral phase transition has been observed at approximately 1273 K in differential thermal analysis measurements, which also allows us to determine the Néel temperature at 742 K. The fitted Mössbauer spectra exposed the presence of a single sextet ascribed to the Fe+3 ions in the tetrahedral site. Finally, magnetic measurements at room temperature indicate the antiferromagnetic character of the sample.

Study of La(Fe, Zn)O3 on the structural properties prepared by sol-gel method

Partial substitution of other metallic ions at La and/or Fe sites of LaFeO3 had been applied to modify the structural properties and for enhancing the properties of its material. In this present work, we prepared LaFeO3 by replacing a portion of Fe3+ with Zn2+ with x = 0.03; 0.05; and 0.07 to study the effect on the structural which prepared by sol-gel method. The samples were identified by X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), Fourier Transform Infrared (FTIR) spectra, Raman spectroscopy, and Ultraviolet-Visible Diffuse Reflectance spectroscopy (UV-Vis DRS). XRD pattern showed all of the samples formed in single crystal and are having an orthorhombic structure with space group Pbnm. The lattice parameters were found to be slightly increased with the increase of Zn concentration. The result of FTIR spectra and Raman spectra also show further information about the formation of LaFeO3 with the distortion due to the replacement of Zn2+ into Fe3+. The absorbance and reflectance of samples are measured using UV-Vis DRS and the energy band gap of LaFe1-x Zn x O3 ( x = 0.03; 0.05; and 0.07) are determined by Tauc plot using Kubelka-Munk function and was found the energy band gap slightly decreased as the concentration of Zn2+ increased.

Magneto-electric coupling and transport properties of LaFeO3–Pb(Zr0.58Ti0.42)O3–organic poly(vinylidene fluoride) nanocomposite

The magneto-electric material of LaFeO3–Pb(Zr0.58Ti0.42)O–poly(vinylidene fluoride) has been prepared by a chemical “pyrophoric reaction technique” and followed by “solid state route”. The formation of LaFeO3, Pb(Zr0.58Ti0.42)O3 and poly(vinylidene fluoride) phases is confirmed by X-ray diffraction technique. The magneto-electric coupling and electrical response have been carried out at room temperature (300 K). The prepared composite reveals the strain mediated magnetoelectric effect at room temperature with longitudinal and transverse configurations at lower frequency region under an external magnetic field. The impedance spectroscopy is used to study the complex electrical modulus and electrical transport properties of the prepared composites at room temperature. The complex modulus and impedance spectra study also helps to understand the mechanism of the electrical transport process, which depicts a non-Debye type of conduction mechanism of the system.

Improvement of spin-charge related magnetoelectric coupling and transport response of rare-earth based eco-friendly multiferroic nanocomposites

Eco-friendly, magnetoelectric LaFeO3–HoMnO3 nanocomposites are synthesized with different weight percentage, and highlighted their observed magnetoelectric coupling, electrical transport and dielectric properties. X-ray diffraction pattern and field emission scanning electron microscope images approve the formation of LaFeO3 and HoMnO3 phases without the presence of any extra phase. These composites reveal the strain mediated magnetoelectric effect with longitudinal (αE33) and transverse (αE31) configurations at lower frequency region under an external magnetic field. Maximum values of αE31 and αE33 are found to ~ 0.54 and ~ 0.31 mV/cm-Oe, respectively for 0.3LaFeO3–0.7HoMnO3 nanocomposites. The electronic transport has been examined by impedance spectroscopy technique for understanding the grain boundary and grain effects in resistive and capacitive behavior of the materials considering an idealized simulated circuit. Temperature dependent Nyquist plots show the non-Debye type phenomena as well as semiconductor in nature (i.e., negative temperature coefficient of resistance) of the materials. Electrical susceptibility reveals the domain motion of the system, which is corresponding to the electrostriction property. The electrical conductivity with frequency follows the Joncher’s single power law and it is controlled through large and small polaron tunneling model. The synthesized nanocomposites are a capable candidate to offer some helpful ideas for developing the lead free device applications.

Microwave synthesis of LaBO3 (B = Co, Fe) perovskites using graphite and citric acid additions

We studied the effects of graphite and citric acid additions on the formation of LaFeO3 and LaCoO3 perovskites upon microwave treatment of crystalline hydrates or nitrate solutions, respectively. The addition of graphite was shown to increase the yield of LaCoO3 perovskite and to result in the formation of crystalline LaFeO3 perovskite even at the microwave treatment stage. Subsequent thermal treatment at 800°C yields single-phase lanthanum ferrite with a high specific surface area (11 m2/g). Due to the addition of citric acid to nitrate solutions, a highly viscous gel forms, which allows preparation of single-phase perovskites with a high specific surface area (up to 34 m2/g) after microwave treatment and calcination. The samples obtained using the admixtures are characterized by a high catalytic activity in methane oxidation. No single-phase oxides form without introduction of these admixtures.

Oxidative Degradation of Organic Dyes Over Supported Perovskite Oxide LaFeO3/SBA-15 Under Ambient Conditions

Supported perovskite oxide, LaFeO3/SBA-15, is investigated for the first time as catalyst for the oxidation of organic dyes using hydrogen peroxide as oxidant. Characterizations such as XRD, XPS, TEM and N2 physisorption isotherms indicate that the supported catalyst has typical perovskite LaFeO3 structure, and the ordered mesoporous structure of SBA-15 remains unchanged after the formation of LaFeO3. Catalytic tests indicate that LaFeO3/SBA-15 has large adsorption capacity, good catalytic performances, and wide working pH ranges (from 2 to 10) for the oxidation of dyes, e.g., Rhodamine B. Moreover, the catalyst can be reused for at least four times without appreciable loss in the activity, and no dissolved Fe3+ ion could be detected by atomic absorption spectrometry after the reaction, suggesting that LaFeO3/SBA-15 is a very stable and active catalyst for the oxidation of dyes in aqueous solution. Comparative tests on various organic dyes, such as reactive brilliant red X-3B, direct scarlet 4BS, methylene blue and Rhodamine B (RhB), indicate that LaFeO3/SBA-15 is more favorable for RhB oxidation, while considerable activity could also be available for other dyes, potentiating its wide applications for industrial removal of dyes. The excellent catalytic performances of LaFeO3/SBA-15 could be attributed to the synergistic effect between SBA-15 and LaFeO3. Supported perovskite oxide LaFeO3/SBA-15 shows active and stable catalytic activity for the oxidative removal of organic dyes using H2O2 as oxidant

Effects of PVA content on the synthesis of LaFeO3 via sol–gel route

LaFeO3 were synthesized via a sol–gel route based on polyvinyl alcohol (PVA). Differential scanning calorimetry (DSC), Thermogravimetric (TG), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FESEM) techniques were used to characterize precursors and derived oxide powders. The effect of the ratios of positively charged valences to hydroxyl groups of PVA (Mn+/–OH) on the formation of LaFeO3 was investigated. XRD analysis showed that single-phase and well-crystallized LaFeO3 was obtained from the Mn+/–OH=4:1 molar ratio precursor at 700°C. For the precursor with Mn+/–OH=2:1, nanocrystalline LaFeO3 with average particle size of ∼50nm was formed directly in the charring procedure. With increase of PVA content to Mn+/–OH=1:1, phase pure LaFeO3 was obtained at 500°C.

LaFeO3 perovskite-type oxide prepared by oxide-mixing, co-precipitation and complex synthesis methods

The perovskite oxide, LaFeO3, was synthesized by three different preparation methods i.e., the calcination of a mixture of La2O3 and Fe2O3 (La-Fe-O), a co-precipitated precursor (La-Fe-OH), La(OH)3 and Fe(OH)3, and a heteronuclear complex (La-Fe-CN), La[Fe(CN)6] · 5H2O. The obtained powders were characterized by thermogravimetric analysis, powder X-ray diffraction, electron microprobe analysis, specific surface area measurement and scanning electron microscopy. The formation of LaFeO3 is clearly recognized for La-Fe-O, La-Fe-OH and La-Fe-CN at calcining temperatures above 1000, 800 and 600°C, respectively. The mean particle diameter of La-Fe-CN calcined at 600°C for 2 hours was 30 nm. The LaFeO3 perovskite oxide powder obtained by the thermal decomposition of La-Fe-CN was most uniform on an atomic level and the nanosized LaFeO3 powder was obtained at low temperatures. Furthermore, the sinterability was good.

Thermodynamic studies on LaFeO3(s)

The enthalpy increments and the standard molar Gibbs energies in the formation of LaFeO3(s) have been measured using a high-temperature Calvet micro-calorimeter and a solid oxide galvanic cell, respectively. The corresponding expression for enthalpy increments is given as:H°(T)−H°(298.15K)(Jmol−1)(±1.2%)=−36887.27+103.53T(K)+25.997×10−3T2(K)+11.055×105/T(K).The heat capacity, the first differential of H°(T)−H°(298.15 K) with respect to temperature, is given as:Cp,m°(T)(JK−1mol−1)=103.53+51.994×10−3T(K)−11.055×105/T2(K).From the measured e.m.f. of the cell, (−)Pt/(LaFeO3(s)+La2O3(s)+Fe(s))//CSZ//(Ni(s)+NiO(s))/Pt(+), and the relevant ΔfGm°(T) values from the literature, the ΔfGm°(LaFeO3, s, T) was calculated, and is given as:ΔfGm°(LaFeO3,s,T)(kJmol−1)(±0.72)=−1319.2+0.2317T(K).The calculated ΔfHm°(LaFeO3, s, 298.15 K) and S°(298.15 K) values obtained using the second law method are −1334.7 kJmol−1 and 128.9 JK−1mol−1, respectively.

Thermal evolution of the microstructure of nanosized LaFeO3 powders from the thermal decomposition of a heteronuclear complex, La[Fe(CN)6] · 5H2O

The thermal decomposition of a heteronuclear complex, La[Fe(CN)6] · 5H2O, leads to the preparation of nanosized single-phase perovskite-type LaFeO3 powders. The microstructural evolution of LaFeO3 with the temperature has been studied by x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The product of the decomposition at 500 °C consists of nanoporous grains which have the morphology of the complex, but diffracting as a monocrystal of LaFeO3. At the higher temperatures, the nanosized particles start to separate from each other, still keeping the shape of the complex grains and forming soft agglomerates. The formation of LaFeO3 from the complex at low temperatures is facilitated by the formation of an orthorhombic transition phase.

ChemInform Abstract: THE STANDARD FREE ENERGY OF THE FORMATION OF LAFEO3 AT 1204 C

The standard free energy of the formation of LaFeO3 was detemined to be −68700±200 cal·mol−1 at 1204°C by the following reaction: 1/2 La2O3(s)+Fe(s)+3/4 O2(g) = LaFeO3(s), based on precise phase equilibria in the Fe–Fe2O3–La2O3 system.