Mechanosynthesis, magnetic and Mössbauer characterization of pure and Ti4+-doped cubic phase BiFeO3 nanocrystalline particles (original) (raw)
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Mechanochemically assisted synthesis of nanocrystalline BiFeO3
Materials Chemistry and Physics, 2013
h i g h l i g h t s < The mechanochemical reaction of BiCl 3 , FeCl 3 and NaOH yields BiFeO 3 and NaCl. < Heating at 600 C improves the crystallization of the pure ferrite phase. < NaCl byproduct is removed by washing of the calcined powder. < BiFeO 3 powder consists of particles of 100 nm formed by crystals of 30 nm. < Magnetic and electric transitions are determined by thermal analyses.
The Journal of …, 2010
Here, we report the effect of reduction in particle size on the temperature dependent magnetization of chemically synthesized BiFeO 3 nanocrystals with average grain size of 55 nm. The X-ray photoelectron spectroscopy results show a significant broadening of binding energy peaks associated to Fe 3+ 2p 3/2 core levels due to the reduced size. Additionally, due to the nanosize effect, the M-H loops show a significant coercivity starting from 390 K with an anomaly located in the vicinity of 150 K in our H c vs T as well as M r /M s(50 kOe) vs T curves. At this temperature, both H c and M r /M s(50 kOe) undergo minima. Additionally, our results for the first time show the evidence of existence of a low temperature anomaly due to spin-glass transition in the range from 40-44 K in the field cooled magnetization curves. In bulk single crystals, this transition is reported to be situated at around 50 K, however, this transition remained so far undiscovered in the recent studies on BiFeO 3 nanoparticles due to the insufficient temperature resolution. The significant shift in this transition toward lower temperature can be attributed to size dependent effects. Our results clearly present new information on the size dependent properties of BiFeO 3 nanoparticles.
Characterization of BiFeO 3 nanopowder obtained by mechanochemical synthesis
Bismuth ferrite nanopowders have been obtained by mechanochemical synthesis. The materials were characterized by high resolution electron microscopy, X-ray diffraction and NIR Raman scattering. The XRD pattern of the powder consists of reflections, characteristic of BiFeO 3 perovskite structure, superimposed on broad maxima that can be ascribed to an amorphous/disordered phase. The analysis of the two broad bands at low 2θ angle yields mean distances of about 3 and 1.8 ˚ A which may be related to Bi O and Fe O bonds, respectively. The powder consists of loosely packed grains with a broad distribution of sizes between a few nm and 45 nm. The grains of sizes larger than about 30 nm exhibit well-developed crystalline structure.
Preparation and characterization of BiFeO 3 nanopowders
Journal de Physique IV (Proceedings), 2005
Conditions for synthesizing single phase BiFeO 3 are critical since the temperature stability range of the phase is very narrow. Moreover, it is also difficult to control oxygen stoichiometry in the sample; hence, various aspects of BiFeO 3 system have to be studied. The fine particles of BiFeO 3 are obtained using a wet chemical route and compared with the same product prepared by a classic solid state reaction. The powders are characterized by using various techniques: X-ray diffraction (XRD) study is carried out for phase determination and lattice parameter calculations; scanning electron microscopy (SEM) to find out grain size and morphology. The sintered bulk materials were characterized (density, porosity, etc.) and correlated with the microstructure. This study underlines the role of the preparation route on the structural characteristic of the obtained nanopowders. Farther investigations on structure-property co-relation are in progress.
Synthesis of high-purity nanocrystalline BiFeO3
Inorganic Materials, 2013
The kinetics of BiFeO 3 formation from xerogel prepared by reverse coprecipitation were studied at different synthesis temperatures. We examined the influence of annealing temperature on the morphology of the reaction products and optimized synthesis conditions, which allowed us to obtain 99.7 wt % pure BiFeO 3 consisting of crystalline grains less than 50 nm in size. Its magnetic properties were investigated.
IEEE, 2016
Pure BiFeO3 nanoparticles were synthesized by a simple sol-gel method namely modified Pechini method. The nanoparticles were calcinated at four different temperatures (450 0 C, 550 0 C, 650 0 C, 750 0 C). Requirement for extra washing step for impurity phase reduction has been eliminated by elongation of the drying duration at oven from 12 hours to 28 hours along with intermediate grinding. FESEM and X-ray Diffraction (XRD) were performed which confirm that the samples calcinated at 450 0 C and 550 0 C show smaller particle size and greater correspondence. Hence XPS was performed on these two samples which showed lower oxygen vacancies for 550 0 C. Finally the SQUID analysis has been carried out for the 550 0 C sample. A higher value of remanent magnetization and coercive field at room temperature has been observed. Besides, an asymmetric shift in the field axis with unsaturated M-H curve may be attributed to the existence of exchange bias effect in the synthesized nanoparticles. Index Terms-Multiferroics, sol-gel, nanoparticles, exchange bias effect. I. INTRODUCTION The quest for multiferroic materials is actuated not only by the simultaneous existence of ferroelectricity and ferromagnetism but also by the possible coupling of their electric and magnetic orderings [1-3]. Such property allows mutual control of the electric polarization with a magnetic field or control of magnetization by an electric field. This magnetoelectric (ME) effect is prodigiously potential in developing novel memory and spintronic devices, spin valves, oscillators, filters, thin film capacitors and sensors [4-6]. Among the available multiferroic materials of type ABO3, BiFeO 3 (BFO) having rhombohedrally distorted perovskite structure with lattice parameters of a = 5.571Å and c = 13.868Å at room temperature with high Curie temperature of T C = 820-850 0 C [1, 2], Neel temperature of T N = 350-380 0 C [3] has turned into a cynosure of many current studies. It has potential applications of magnetoelectric coupling at temperatures around room temperature [1, 5, 7, 8]. In BFO Bi 3+ contributes to ferroelectricity whereas antiferromagnetism is attributed to Fe 3+ ions. BiFeO 3 exhibits anti-ferromagnetic G-type spin conf guration along the [111] c or [001] h directions in its pseudocubic or rhombohedral structure. It has a cycloid spin structure with a periodicity of
Chemistry of Materials, 2011
In situ synchrotron radiation powder X-ray diffraction (SR-PXRD) was applied to study the formation and growth of BiFeO 3 nanocrystals, revealing that phase pure BiFeO 3 can be obtained in high-temperature, high-pressure aqueous solution using Bi(NO 3 ) 3 and Fe(NO 3 ) 3 3 9H 2 O as precursors and KOH as mineralizer. The method gives a rapid way for preparation of nanomaterials, and the formation of BiFeO 3 can be finished within seconds after its initial nucleation in nearcritical aqueous solution. As proof of concept BiFeO 3 nanocrystals were subsequently synthesized in a continuous flow supercritical system and for reference also in autoclaves. High resolution multitemperature SR-PXRD data were measured between 100 and 1000 K with a step size of 100 K. The magnetic properties of both the autoclave and the continuous flow samples are studied.
Inorganic Chemistry, 2013
Synthesis of high-purity BiFeO 3 is very important for practical applications. This task has been very challenging for the scientific community because nonstoichiometric Bi x Fe y O z species typically appear as byproducts in most of the synthesis routes. In the present work, we outline the synthesis of BiFeO 3 nanostructures by a combustion reaction, employing tartaric acid or glycine as promoter. When glycine is used, a porous BiFeO 3 network composed of tightly assembled and sintered nanocrystallites is obtained. The origin of high purity BiFeO 3 nanomaterial as well as the formation of other byproducts is explained on the basis of metal−ligand interactions. Structural, morphological, and optical analysis of the intermediate that preceded the formation of porous BiFeO 3 structures was accomplished. The thorough characterization of BiFeO 3 nanoparticles (NPs) included powder Xray diffraction (XRD); scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM); thermogravimetric analysis (TGA); UV−vis electronic absorption (diffuse reflectance mode), Raman scattering, Mossbauer, and electron paramagnetic resonance (EPR) spectroscopies; and vibrating sample magnetometry (VSM). The byproducts like β-Bi 2 O 3 and 5 nm Bi 2 Fe 4 O 9 NPs were obtained when tartaric acid was the promoter. However, no such byproducts were formed using glycine in the synthesis process. The average sizes of the crystallites for BiFeO 3 were 26 and 23 nm, for tartaric acid and glycine promoters, respectively. Two band gap energies, 2.27 and 1.66 eV, were found for BiFeO 3 synthesized with tartaric acid, obtained from Tauc's plots. A remarkable selective enhancement in the intensity of the BiFeO 3 A 1 mode, as a consequence of the resonance Raman effect, was observed and discussed for the first time in this work. For glycine-promoted BiFeO 3 nanostructures, the measured magnetization (M) value at 20 000 Oe (0.64 emu g −1 ) was ∼5 times lower than that obtained using tartaric acid. The difference between the M values has been associated with the different morphologies of the BiFeO 3 nanostructures.