Magnetic and optical investigations on LaFeO3 powders with different particle sizes and corresponding ceramics (original) (raw)
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Advances in Materials Science and Engineering, 2012
Nanosized LaFeO3material was prepared by 3 methods: high energy milling, citrate gel, and coprecipitation. The X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) show that the orthorhombic LaFeO3phase was well formed at a low sintering temperature of 500°C in the citrate-gel and co-precipitation methods. Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations indicate that the particle size of the LaFeO3powder varies from 10 nm to 50 nm depending on the preparation method. The magnetic properties through magnetization versus temperatureM(T)and magnetization verses magnetic fieldM(H)characteristics show that the nano-LaFeO3exhibits a weak ferromagnetic behavior in the room temperature, and theM(H)curves are well fitted by Langevin functions.
Nanocrystalline LaFeO 3 powders synthesized by the citrate–gel method
Materials Letters, 2006
A novel sol–gel process was developed for preparing nano-sized, perovskite-type LaFeO3 powder by the thermal decomposition of the gel-complex of LaFe–(C6H8O7·H2O). The structural evolution has been systematically investigated by X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetric analysis (TGA). Perovskite powder of ∼ 25 nm size could be obtained at a temperature of ∼ 600 °C without formation of any secondary phases of La2O3 and Fe2O3 single oxides and no requirements of high temperature/vacuum/pH control etc. Analysis of the X-ray powder diffraction data showed a decrease in the value of lattice strains with increasing decomposition temperature, whereas the particle size increases with increasing decomposition temperature.
Solid State Ionics 231 (2013) 43–48, 2013
The preparation of a nano-sized LaFeO3 powder by a soft-chemistry method using starch as complexing agent is described herein. Phase evolution and development of the specific surface area during the decomposition process of (LaFe)-gels were monitored up to 1000 °C. A phase-pure nano-sized LaFeO3 powder with high specific surface area of 25.7 m2/g and a crystallite size of 37 nm was obtained after calcining at 570 °C. TEM investigations reveal a porous powder with particles in the range of 20 to 60 nm. Calcinations to 1000 °C result in crystallite sizes up to 166 nm. The dilatometric measurements of the sintering behaviour show that the beginning of shrinkage of pellets from the nano-sized powder is downshifted by more than 300 °C compared to the coarse-grained mixed-oxide powder. The orthorhombic ⇆ rhombohedral phase transition was observed at 980 °C in DTA measurements for the coarse-grained ceramic bodies. The enthalpy change (ΔH) during the phase transition and the thermal expansion coefficient (αdil) for the ceramics were determined as 410 J/mol and 11.8·10− 6 K− 1, respectively. Whereas the enthalpy changes during the phase transition of the nano-sized LaFeO3 powders are ≤ 200 J/mol.
Structure, Optical and Magnetic behavior of LaFeO 3 and LaFe 0.9 Ni 0.1 O 3- by combustion method
— In the present work, we report the pure LaFeO 3 and Nickel doped (LaFe 0.9 Ni 0.1 O 3- samples for tunable optical and magnetic properties. The samples were prepared by citrate combustion method. This method offers us a very rapid synthesis of the samples. Prepared samples were kept in hot plate to initiate the combustion process. Samples were grounded and calcined in furnace at 800 O C for 2 Hrs. The XRD analysis confirms the phase formation of LaFeO 3 and Ni doped LaFeO 3. The local structure of these samples was studied using Raman spectroscopy. Raman analysis shows, Ni 2+ doping effect on the tilt and stretching phonon modes of LaFeO 3. SEM picture shows fine grains were grown with random shapes. Optical measurements were done using a U-V visible spectrometer. The Ni 2+ ion doping significantly broadens the absorption regions. The enhancement of room temperature magnetization value is observed from the M-H curve measured using VSM. Thus, the optical and magnetic properties were significantly influenced by Ni 2+ doping and can be tuned for functional device applications.
Magnetic, Raman and M € ossbauer properties of double-doping LaFeO 3 perovskite oxides
La 0.8 Ca 0.2Àx Pb x FeO 3 compounds were synthesized by the solegel method. M€ ossbauer study: presence of Fe 3þ tetrahedral site and a doublet for x ¼ 0 sample. For x > 0 samples, the M€ ossbauer results revealed the presence of Fe 3 O 4 phase. The substitution of Ca 2þ by Pb 2þ introduces a change on the magnetization. Competition between tetrahedral FM and octahedral AFM interactions. a b s t r a c t The La 0.8 Ca 0.2Àx Pb x FeO 3 (x ¼ 0.00, 0.05, 0.10, 0.15 and 0.20) compounds were prepared by the solegel method using the citric acid route. The structural study revealed that all samples crystallized in the Pnma orthorhombic structure with the apparition of Ca 2 Fe 2 O 5 and Fe 3 O 4 secondary phases for samples with x ! 0.05, confirmed by the Raman spectroscopy study. The fitted M€ ossbauer spectra exposed, for x ¼ 0.00 sample, the presence of a one sextuplet, related to the Fe 3þ ion in the tetrahedral site, and a doublet. However, for x > 0.00 samples, the fit results showed the apparition of other sextuplets related to the Fe 3 O 4 phase. The percentage of this latest phase was found to increase and to reach a maximum for the x ¼ 0.10 sample and to decrease after for x ¼ 0.15 and 0.20 samples. The variation of the magnetization (M) as a function of the temperature (T), under an applied magnetic field of 0.05 T, showed the presence of a ferromagneticeparamagnetic transition. The magnetic study exposed that the magnetization decreases first for x 0.10 samples and then increases for the two other samples. This behavior was related to the competition between the Fe 3þ eFe 3þ tetrahedral ferromagnetic interactions and the octahedral antiferromagnetic ones between Fe 3þ and Fe 2þ ions.
Journal of Solid State Chemistry 287 (2020) 121380, 2020
Nanocrystalline Li0.5Fe2.5O4 was prepared by a starch-based soft-chemistry synthesis. Calcining of the (LiFe)-gel between 350 and 1000 °C results in Li0.5Fe 2. O4 powders with crystallite sizes from 13 to 141 nm and specific surface areas between 35 and 7.1 m^2 g-1. XRD investigations reveal the formation of ordered Li0.5Fe2.5O4. Sintering between 1050 and 1250 °C leads to ceramics with relative densities of 67 95 % consisting of grains between 0.3 and 54 µm. As the sintering temperature increases a rising weight loss of the ceramic samples was observed due to the loss of Li2O. Temperature-dependent magnetic measurements indicate a superparamagnetic behaviour for the nano-sized samples. Field-dependent measurements at 3 K of ceramics sintered between 1050 and 1200 °C show increasing saturation magnetization values (M s) of 70.0 to 73.0 emu g-1 most likely due to the formation of lithium vacancies and a decrease of the inversion parameter. The magnetization drops down to 67.7 emu g-1 after sintering at 1250 °C caused by the formation of hematite. Diffuse reflectance spectra reveal an indirect allowed band gap decreasing from 1.93 to 1.60 eV depending on thermal treatment. DSC measurements of the order - disorder phase transition on nano-sized powders and bulk ceramics exhibit transition temperatures between 734 and 755 °C and enthalpy changes (trs H) ranging from 5.0 to 13.5 J g-1. The linear thermal expansion coefficient was found to be 11.4 10^- 6 K-1 .