镍锌纳米晶铁氧体的络合溶胶-凝胶法合成及表征

利用乙酰丙酮(AcAcH)络合溶胶-凝胶法合成了Ni0.5Zn0.5Fe2O4(NZFO)尖晶石型软磁铁氧体。采用傅里叶变换红外光谱(FTIR)技术研究了Fe、Zn、Ni 3种溶胶中AcAcH与Fe3+、Zn2+、Ni2+的结合形式,通过比较Fe、Zn、Ni溶胶与未添加AcAcH的Fe、Zn、Ni甲醇溶液的红外光谱发现,分别在1 532 cm-1、1 520 cm-1和1 520 cm-1处多了一个吸收峰,说明AcAcH都能与3种离子发生螯合反应。采用X射线衍射(XRD)、高分辨透射电子显微镜(HRTEM)、物性测量系统(PPMS)分别表征NZFO铁氧体的相组成、微结构以及磁性能。XRD测试结果表明,NZFO铁氧体为单一尖晶石相结构;HRTEM透射结果表明,NZFO为片状,大小均匀,尺寸45 nm左右;PPMS研究结果表明,NZFO铁氧体的饱和磁化强度(Ms)和矫顽力(Hc)分别为36 emu.g-1和167 Oe。     

Enhanced dielectric and magnetic properties of Cr / Co and Mn co-doped single phase multiferroic bismuth ferrite nanoparticles

Multiferroic nanoparticles of single-phase bismuth ferrite (BiFeO₃ or BFO) by choosing transition metal ions of chromium (Cr)/cobalt (Co) in A-sites and manganese (Mn) in B-sites were synthesized by using sol-gel autocombustion method. X-ray diffraction (XRD) data reveal the existence of rhombohedrally distorted perovskite structure for all the samples. High resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDAX) studies were carried out to estimate the particle size, morphology along with the chemical purity of the samples. Dielectric studies as a function of frequency and temperature resemble typical space charge polarization with almost negligible dielectric losses in the doped samples. Magnetic measurements using vibrating sample magnetometer reveals the considerable enhancement in the magnetic order in Co/Cr and Mn co-doped samples. The obtained structural, microstructural, dielectric and magnetic results were well recommended that the influence of co-doping in BFO will certainly modify its spin cycloid structure and hence enhanced properties in these doped samples. Thus, these co-doped samples were suggested to be well suitable for the multifunctional based devices such as spintronic, multifunctional memories, and for sensors.     

A highly coercive carbon nanotube coated with Ni0.5Zn0.5Fe2O4 nanocrystals synthesized by chemical precipitation-hydrothermal process

Novel magnetic composites (Ni_0.5Zn_0.5Fe₂O₄-MWCNTs) of multi-walled carbon nanotubes (MWCNTs) coated with Ni_0.5Zn_0.5Fe₂O₄ nanocrystals were synthesized by chemical precipitation-hydrothermal process. The composites were characterized by X-ray powder diffractometer (XRD), X-ray photoelectron spectrometer (XPS), Fourier transform infrared spectroscopy (FTIR), Mössbauer spectroscopy (MS), transmission electron microscopy (TEM), and selected area electron diffraction (SAED), etc. A temperature of about 200 °C was identified to be an appropriate hydrothermal condition to obtain Ni_0.5Zn_0.5Fe₂O₄-MWCNTs, being lower than the synthesis temperature of a single-phase Ni_0.5Zn_0.5Fe₂O₄ nanocrystals. The sizes of Ni_0.5Zn_0.5Fe₂O₄ in the composites were smaller than those of Ni_0.5Zn_0.5Fe₂O₄ nanocrystals in single phase. The composites exhibited more superparamagnetic than Ni_0.5Zn_0.5Fe₂O₄ nanocrystals in their relaxation behaviors. The magnetic properties measured by a vibrating sample magnetometer showed that the composites had a high coercive field of 386.0 Oe at room temperature, higher than those of MWCNT and Ni_0.5Zn_0.5Fe₂O₄ nanocrystals.     

Highly improved dielectric behaviour of ferronematic nanocomposite for display application

We report the investigation of influence of nickel zinc ferrite magnetic nanoparticles (NZFO (Ni_0.5Zn_0.5Fe₂O₄)) on phase transition, optical and dielectric properties in a nematic liquid crystal (NLC). The interaction of NZFO nanoparticles with NLC was confirmed by the formation of ferronematic droplets due to the transfer of magnetic orientational effect onto the underlying NLC matrix. The doping results in shift of nematic to isotropic transition to low-temperature region. An enhancement in the value of refractive index is observed in the nematic region after the addition of NZFO nanoparticles. The dielectric constant of NLC was remarkably enhanced by 10 times after doping, which is found to be maximum at 0.1 wt% concentration of NZFO nanoparticles. The decrease in the value of dissipation factor in low-frequency region shows that the magnetic nanoparticles are able to trap ionic impurities effectively. The obtained results suggest that the optimum amount of doping concentration is 0.1 wt% of NZFO nanoparticles in NLC due to high dielectric constant with low dissipation factor and high refractive index with high dispersive power at room temperature.     

Ni–Zn ferrite-loaded superparamagnetic amorphous carbon nanotubes through a facile route

Partial filling of mixed ferrite (Ni_0.5Zn_0.5Fe₂O₄; NZFO) nanoparticles into the amorphous carbon nanotubes (aCNTs) cavity is achieved by simple mixing of the aqueous dispersions of the two (aCNTs and NZFO) at room temperature. The process of incorporation of the nanoparticles into the aCNT cavity is solely mediated by the capillary action of the liquid. NZFO nanoparticles were homogeneously dispersed in the aqueous solution but after mixing they are sparsely distributed into the aCNT channel as a result of the capillary action. The encapsulation of the nanoparticles into the aCNTs amorphous shield was established by means of X-ray diffraction, transmission electron microscopy, Fourier transformed infrared spectroscopy, and Raman spectroscopic analysis. Such entrapment of the nanoparticles causes the composite nanotubes superparamagnetic in nature with blocking temperature (T _B) at 15 K. However, compared to the powder NZFO nanoparticles, T _B appears more sharply and at relatively lower temperature. Low filling density and the spatial confinement of the nanoparticles lessen the inter-particle interactions and the polydispersity within the NZFO nanoparticles which are manifested in their altered magnetic behavior.     

One-dimensional NiCuZn ferrite nanostructures: Fabrication, structure, and magnetic properties

Ni_0.5−xCu_xZn_0.5Fe₂O₄ (0.0≤x≤0.5) ferrite nanofibers with diameters of 80-160 nm have been prepared by electrospinning and subsequent heat treatment. Both the average grain size and lattice parameter are found to increase with the addition of copper. Fourier transform infrared spectra indicate that the portion of Fe³⁺ ions at the tetrahedral sites move to the octahedral sites as some of the substituted Cu²⁺ ions get into the tetrahedral sites. Vibrating sample magnetometer measurements show that the coercivity of these ferrite nanofibers decreases with increasing Cu concentration, whereas the specific saturation magnetization initially increases, reaches a maximum value at x=0.2 and then decreases with the Cu content further increase. Notable differences in magnetic properties at room temperature (298 K) and 77 K for the Ni_0.3Cu_0.2Zn_0.5Fe₂O₄ nanofibers and corresponding powders are observed and mainly arise from the grain size and morphological variations between these two materials.     

Highly selective synthesis of diphenyl methane via liquid phase benzylation of benzene over cobalt doped zinc nanoferrite catalysts at mild conditions

Liquid phase benzylation of benzene with benzyl chloride was investigated over different compositions of cobalt zinc ferrite (Co_xZn_1-xFe₂O_4, x-0.0, 0.25, 0.5, 0.75, 1.0) nano composites, synthesized by sol–gel method. The un-substituted cobalt ferrite catalyst exhibited excellent activity among the series effecting complete conversion of benzyl chloride in 60?min at 90?°C with 100% selectivity for diphenyl methane. The effect of various reaction parameters on the reaction was studied. Higher benzylation activity of cobalt ferrite nanocomposite is attributed to the presence of higher quantities of moderately acidic sites and a good correlation was observed between surface acidity and benzylation activity of catalysts. The catalysts are reusable without any significant structural change as indicated by X-ray Diffraction (XRD) and Atomic Absorption Spectrophotometer (AAS).     

Microstructure,magnetic properties and exchange–coupling interactions for one-dimensional hard/soft ferrite nanofibers

SrFe₁₂O₁₉ (SFO)/Ni_0.5Zn_0.5Fe₂O₄ (NZFO) composite ferrite nanofibers with diameters about 120 nm have been prepared by the electrospinning and calcination process. The SFO/NZFO composite ferrites are formed after calcined at 700 °C for 2 h and the composite nanofibers with various mass ratios obtained at 900 °C are fabricated from NZFO grains about 16–40 nm and SFO grains of 19–45 nm with a uniform phase distribution. With the SFO ferrite content increasing, the coercivity (H_c) and remanence (M_r) for the composite ferrite nanofibers initially increase, reaching maximum values of 379.8 kA/m (297 K) and 242.2 kA/m (77 K), 39.1 Am²/kg (297 K) and 53.5 Am²/kg (77 K), respectively, at a mass ratio (SFO:NZFO) of 4, and then show a reduction tendency with a further increase of the mass ratio. This enhancement in magnetic properties is attributed to the competition of the exchange–coupling interaction and the dipolar interaction in the composite nanofibers.     

Nanocrystalline Ni0.6Zn0.4Fe2O4: A novel semiconducting material for ethanol detection

The structure and crystal phase of the nanocrystalline powders of Ni_1−xZn_xFe₂O₄ (0 ≤ x ≤ 0.5) mixed ferrite, synthesized by ethylene glycol mediated citrate sol-gel method, were characterized by X-ray diffraction and microstructure by transmission electron microscopy. Further studies by Fourier transform infrared spectroscopy were also conducted. Moreover, DC electrical properties of the prepared nanoparticles were studied by DC conductivity measurements. The response of prepared Ni_1−xZn_xFe₂O₄ mixed ferrites to different reducing gases (ethanol, hydrogen sulfide, ammonia, hydrogen and liquefied petroleum gas) was investigated. In particular, Ni_0.6Zn_0.4Fe₂O₄ composition exhibited high response to 100 ppm ethanol gas at 300 °C. Incorporation of palladium further improved the response, selectivity and response time of Ni_0.6Zn_0.4Fe₂O₄ to ethanol gas with the blue shift in the operating temperature by 25 °C.     

Preparation and ferromagnetic properties of Ni0.5Zn0.5Fe2O4/polyaniline core–shell nanocomposites

Magnetic Ni_0.5Zn_0.5Fe₂O₄‐crosslinked polyaniline composites with a core–shell structure were prepared in the presence of Ni_0.5Zn_0.5Fe₂O₄ magnetic powder in a toluene solution containing iron chloride as a surfactant and dopant. Structural characterization by Fourier transform infrared, X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy proved that Ni_0.5Zn_0.5Fe₂O₄ in the composites was responsible for the ferromagnetic behavior of the composites. The effects of the polyaniline and temperature on the magnetic properties of the Ni_0.5Zn_0.5Fe₂O₄/polyaniline composites were studied with electron paramagnetic resonance and superconducting quantum interference device techniques. A clear evolution from ferromagnetic resonance to electron paramagnetic resonance was observed as a function of temperature, which was related to the passage through the Curie point (～420 K). The magnetic properties of the resulting composites showed ferromagnetic behavior, such as high‐saturated magnetization (saturation magnetization = 35–39 emu/g), low coercive force (coercivity = 22–28 G), and low blocking temperatures (～23 K). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2657–2664, 2006     

Comparison of the properties of PZTNB-1 + Ni<Subscript>0.9</Subscript>Co<Subscript>0.1</Subscript>Cu<Subscript>0.1</Subscript>Fe<Subscript>1.9</Subscript>O<Subscript>4 − δ</Subscript> magnetoelectric composites manufactured from components synthesized by Sol-Gel processes

Processes were developed for manufacturing mixed magnetoelectric (ME) composites (100 − x) wt % PZTNB-1 + x wt % Ni_0.9Co_0.1Cu_0.1Fe_1.9O_{4 − δ} using sol-gel processes to synthesize piezoelectric and magnetostrictive components; these processes provide composite ceramics having different connectivity types with the same composition. When PZTNB-1 prepared by the sol-gel process is used for manufacturing the composites, there is a deep one-way doping of the piezoelectric with ferrite constituents, and this doping considerably reduces the degree of tetragonal distortion of the perovskite unit cell to the point of disappearance. In contrast, when coarse-grained PZTNB-1 powder and a ferrite nanopowder prepared by the sol-gel process are used, undesirable doping is completely inhibited. This type of composite has the highest ME transduction efficiency, by two or more times exceeding the ME ceramics of the same composition manufactured by other processes.     

Magnetic properties of binary and ternary mixed metal oxides NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> and Zn<Subscript>0.5</Subscript>Ni<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> doped with rare earths by sol—gel synthesis

The spinel-type ferrites NiFe₂O₄ and Zn_0.5Ni_0.5Fe₂O₄ modified by lanthanide ions Eu³⁺ and Tb³⁺ were prepared by a sol—gel process with propylene oxide as a gelating agent. The phase homogeneity of the samples was tested by XRD and Mössbauer spectroscopy. Transmission electronic microscopy used for characterisation of the morphology of the samples revealed nanosized powdered samples with a narrow distribution of particle sizes. It was noted that the presence of Ln³⁺ ions influenced the magnetic properties of nanosized NiFe₂O₄ and Ni_0.5Zn_0.5Fe₂O₄ ferrites. The dependence of the magnetic properties of the samples on the rare-earth doping may be explained by the different grain sizes. The saturation magnetisation tends to decrease with increasing rare-earth doping and decreasing crystallite size. A similar trend was observed for the coercive field, with the exception of the Tb³⁺-doped Zn_0.5Ni_0.5Fe₂O₄ where it remained the same as in the pure ferrite.     

Synthesis and characterization of Ni<Subscript>0.6</Subscript>Zn<Subscript>0.4</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nano-particles obtained by auto catalytic thermal decomposition of carboxylato-hydrazinate complex

Ni_0.6Zn_0.4Fe₂O₄ nano-particles have been synthesized by self-propagating auto-combustion of nickel zinc ferrous fumarato-hydrazinate complex. The precursor complex has been characterized by chemical analysis, IR, AAS, thermal analysis and isothermal mass loss studies. The precursor on ignition undergoes self-propagating auto combustion to give Ni_0.6Zn_0.4Fe₂O₄. The X-ray diffraction studies confirmed the single phase formation of nano-size ‘as synthesized’ Ni_0.6Zn_0.4Fe₂O₄. TEM observation showed the average particle size to be 20 nm. Infrared and magnetization studies were also carried out on the ‘as synthesized’ Ni_0.6Zn_0.4Fe₂O₄. The lower value of saturation magnetization and higher Curie temperature of ‘as synthesized’ ferrite also hint at the nano size nature.     

Synthesis and visible-light photocatalysis capability of BiFeO3–(Na0.5Bi0.5)TiO3 nanopowders by a sol–gel method

Multiferroic BiFeO₃–(Na_0.5Bi_0.5)TiO₃ (BFO–NBT) nanopowders were successfully synthesized by a sol–gel method, and the visible-light photocatalytic and magnetic properties of BFO–NBT nanopowders were investigated. X-ray diffraction results indicated that the adding of NBT and the excess of natrium source could suppress the formation of secondary phases and made it easier to obtain single perovskite phase. High photoactivity of this catalyst for Rhodamine B (RhB) degradation under visible-light irradiation was detected, which is due to narrow band gap energy of 2.08 eV, higher surface area and pure phase compounds with no or less amounts of impurities. The BFO–NBT nanopowders showed a weak ferromagnetic order at room temperature, which should be attributed to the size-confinement effects of the nanostructures. It is suggested that BFO–NBT is a kind of new narrow band gap semiconductor visible-light photocatalyst with broad application prospects, in addition to potential applications for novel magnetoelectric devices.     

Synthesis of multielement ferrites and their silica composites

Ferrites of composition M_0.2Co_0.4Zn_0.4Fe₂O₄ with M = Cu²⁺, Mn²⁺ and Ni²⁺ were prepared by citrate complex method. Later, their composites with silica have also been obtained by a simple route. The citrate complex precursors of multielement ferrites were characterized by FTIR spectroscopy and thermal analysis, been found a similar behavior for the three systems. The thermal treatment (at 400, 600 and 800 °C) of precursors gives, as result, the spinel type cubic ferrite pure when the ions substituted were copper and nickel; when manganese was used an hematite phase was obtained as contaminant at 800 °C. The presence of all ions involved and the particle size was corroborated by EDX analysis and measured from a TEM micrograph, respectively. The magnetic parameters related to magnetic properties, magnetization and coercivity, were different depending of the chemical composition of the ferrite and the thermal treatment temperature, as it was expected. At room temperature, the values obtained were near to those reported for Co-ferrite in bulk. The synthesis route of the composites M_0.2Co_0.4Zn_0.4Fe₂O₄-SiO₂, proposed in this work, gives as result magnetic nanoparticles in an amorphous silica matrix. Their magnetic properties were depending on weight percentage of the magnetic phase in the composite.     

Novel polyaniline-LiNi0.5La0.02Fe1.98O4 nanocomposites prepared via an in situ polymerization

Polyaniline (PANI)-LiNi_0.5La_0.02Fe_1.98O₄ nanocomposites were synthesized by an in situ polymerization of aniline in the presence of LiNi_0.5La_0.02Fe_1.98O₄ ferrite. The products were characterized by Fourier transform infrared (FTIR), atomic force microscopy (AFM), powder X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). FTIR spectra and XRD indicated the formation of the PANI-LiNi_0.5La_0.02Fe_1.98O₄ composites. AFM study was shown that the average size of samples was less than 100 nm and the ferrite particles had an effect on the morphology of composites. The nanocomposites under applied magnetic field exhibited the hysteresis loops of the ferrimagnetic nature, the saturation magnetization and the coercivity varied with the ferrite content. The bonding model for the composites was also studied.     

Effect of varying the acid to metal ion ratio R on the structural and magnetic properties of SiO2-doped Ni-Zn ferrite

A nitrate-citrate-silica gel was prepared from metallic nitrates, citric acid and tetraethoxysilane (TEOS) by sol-gel process with different citric acid to metal nitrates ratio R, and it was further used to synthesize Ni_0.5Zn_0.5Fe₂O₄/20 wt% SiO₂ nanocomposites by auto-combustion. The effect of varying the citric acid to metal nitrates ratio R on the structural and magnetic properties of the composites were studied by IR, ²⁹Si CP/MAS NMR, XRD, EPR and SQUID measurements. The nitrate-citrate-silica gels exhibited self-propagating combustion behavior, and it directly transformed into nanosized (14-22 nm) NiZn ferrite particles with spinel crystal structure after combustion. The R value in the starting solution affects the magnetic interaction between NiZn ferrite and silica, and then determines the particle size. Further, varying the R value has a direct effect on the EPR parameters (ΔH_PP, g factor, N_S and T₂) and SQUID parameters (M_s, M_r and H_c) of the as-synthesized powder.     

Ultrasonic-assisted synthesis of PMMA/Ni0.5Zn0.5Fe2O4 nanocomposite in mixed surfactant system

PMMA/Ni_0.5Zn_0.5Fe₂O₄ nanocomposite with superparamagnetic behavior was synthesized by in situ emulsion polymerization of methylmethacrylate (MMA) monomer in the presence of Ni_0.5Zn_0.5Fe₂O₄ colloidal suspension assisted by ultrasonic irradiation. The obtained samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). XRD and FT-IR spectra confirmed the formation of PMMA/Ni_0.5Zn_0.5Fe₂O₄ nanocomposite. TEM images showed that Ni_0.5Zn_0.5Fe₂O₄ nanoparticles with the particle sizes of about 12 nm were well dispersed in the polymer matrix. The nanocomposite at room temperature exhibited superparamagnetic behavior under applied magnetic field. The formation mechanism of PMMA/Ni_0.5Zn_0.5Fe₂O₄ nanocomposite was proposed as well.     

Observation of enhanced room temperature multiferroicity in nanoparticles BiFeO3

Impurity free monophasic rhombohedral BiFeO₃ (BFO) nanoparticles are synthesized by sol?Cgel method. Effect of processing technique and particle size are found to influence the dielectric, ferroelectric, magnetic and leakage behavior of BFO ceramic prepared by sol?Cgel as well as conventional solid state reaction route. From XRD analysis it is observed that bulk BFO sample showed rhombohedral structure (R3c) along with other impurity phases, which become suppressed with the decrease of particles size to few nanometers. The dielectric behavior and leakage current characteristic of the samples were improved significantly in nanoparticles of BFO. Ferroelectric hysteresis loops of sintered bulk BFO ceramic is found to change its shape from semi elliptical lossy P?CE features to a typical ferroelectric feature with improved remnant and saturation polarization value for the particle size down to nanometer scale. Furthermore, BFO nanoparticles also showed a good ferromagnetic M?CH hysteresis loop with enhanced saturation magnetization value of 0.138?emu/mg.     

Synthesis and structure of phosphates M<Subscript>0.5</Subscript>Ti<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Phosphates M_0.5Ti₂(PO₄)₃ (M = Ni, Zn) were synthesized by the sol-gel method and characterized by the methods of X-ray diffraction, IR spectroscopy, and electronic microprobe analysis. Structures of Ni_0.5Ti₂(PO₄)₃ and Zn_0.5Ti₂(PO₄)₃ were studied by Rietveld method using the X-ray powder diffraction data.