钐掺杂的W型钐铁氧体Ba1-xSmx（MnZn）0.4Al0.2CoFe16O27制备及电磁性能研究

采用柠檬酸溶胶-凝胶法制备钐掺杂的W型铁氧体Ba1-xSmx(MnZn)0.4Al0.2CoFe16O27(x=0.0,0.1,0.2,0.3),通过X射线衍射(XRD)、电镜扫描(SEM)及矢量网络分析仪考察了钐掺杂量对铁氧体物相组成及其电磁性能的影响。结果表明,当x≤0.1时,得到单一晶型的W型钐铁氧体;x≥0.2时,出现了SmFeO3及Mn2AlO4晶相。另外,在1～18GHz频率范围内测定了样品的电磁参数,发现当Sm3+掺杂量x=0.1时,钐铁氧体的电磁性能达到最优,最大吸收率为-14.4dB,在雷达波频段内吸收率小于-7.5dB。     

Preparation and magnetic properties of barium hexaferrite nanorods

The barium hexaferrite nanorods were successfully prepared by sol–gel technique combined with polymethylmethacrylate as template. The crystal structure, morphology and magnetic properties of BaFe₁₂O₁₉ with different shape were investigated with X-ray diffraction, field emission scanning electron microscope and vibrating sample magnetometry. The results show that diameters and lengths of magnetic nanorods are about 60 nm and 300 nm, respectively. The coercivity of rod-shaped BaFe₁₂O₁₉ is increased to 5350 Oe, in comparison with 4800 Oe with plate-shape. The formation mechanism of BaFe₁₂O₁₉ nanorods and reasons resulting in high coercivity are discussed.     

Synthesis of barium hexaferrite by the co-precipitation method using acetate precursor

Fine particles of barium hexaferrite were synthesised by a chemical co-precipitation method using acetate-nitrate (barium acetate + iron nitrate) precursors. The thermal properties, phase composition and morphology of hexaferrite powders were studied. Simultaneous DTA/TG results confirmed by those obtained from XRD and VSM, indicated that the formation of barium hexaferrite occurs at a relatively low temperature of 710°C. This temperature is affected by the Fe³⁺/Ba²⁺ molar ratio. The SEM investigations revealed that the mean particle size of barium hexaferrite increases with increasing calcination temperature. In this system the Fe³⁺/Ba²⁺ molar ratio of 12 (stoichiometric ratio) is favourable.     

Catalytic activity and magnetic properties of barium hexaferrite prepared from barite ore

Barium hexaferrite (BaFe₁₂O₁₉) has traditionally been used in permanent magnets and more recently used for high density magnetic recording. The classical ceramic method for the preparation of barium hexaferrite consists of firing mixture of chemical grade iron oxide and barium carbonate at high temperature. In this paper a mixture of chemical grade hematite, barium oxide and predetermined mixtures of iron oxide ore and barite ore containing variable amounts of coke were used to prepare barium hexaferrite (BaFe₁₂O₁₉) as a permanent magnetic material. The mixtures were mixed in a ball mill and fired for 20 h in a tube furnace at different temperatures (1100, 1150, 1200 and 1250 °C). XRD, magnetic properties, porosity measurements and catalytic activity were used for characterization of the produced ferrite. The results of experiments showed that the optimum conditions for the preparation of barium hexaferrite are found at 1200 °C for the mixture of chemical grade hematite and barium oxide. It was also found that the barium hexaferrite can be prepared from the iron and barite ores at 1200 °C. The addition of coke enhanced the yield of barium hexaferrite and improved its physicochemical properties. Samples prepared from ores with coke% = 0 show the most acidic active sites, they show a higher catalytic activity towards H₂O₂ decomposition. With addition of coke the catalytic activity decreases due to the poisoning effect of carbon on the available active site.     

Study of morphological and magnetic properties of microwave sintered barium strontium hexaferrite

Magnetic materials are important electronic materials that have a wide range of industrial and commercial applications. Barium strontium hexaferrite (Ba_0.5Sr_0.5Fe₁₂O₁₉-BSF) were prepared by a sol–gel method using d-Fructose as fuel and the heat treatment was carried out in a microwave furnace. The effects of the sintering temperature on the morphology, crystalline structure and magnetic properties are studied. Sintering temperature affected the grains in compact samples. The sintered product possessed dense microstructure with clear micro grains and is in consistence with the XRD analysis based on the peak intensity of the (107) plane. Magnetic measurement shows that the barium strontium hexaferrite sample sintered at 1,150?°C has the coercive field of 1,998 Gauss, remnant magnetization of 38.87?emu/g and the saturation magnetization of 53.44?emu/g.     

Synthesis and magnetic properties of conventional and microwave calcined barium hexaferrite powder

Single phase nanoparticles of barium hexaferrite (BaFe₁₂O₁₉–BaF) were synthesized by sol–gel method using metal nitrates as source and d-Fructose as a fuel. The prepared precursors were calcined by two different calcination techniques, using conventional furnace and microwave furnace. The samples are characterized using powder X-ray diffraction, theromogravimetric analysis and vibration sample magnetometer. Thermal analysis studies showed exothermic and endothermic reaction peaks from room temperature to 1,200 °C. X-ray diffraction studies established the formation temperature of single phase BaFe₁₂O₁₉. HR-SEM results showed the dispersed particles of hexagonal structure in platelet form. The broad hysteresis loop showed that the barium hexaferrite powder was in good crystalline nature.     

Preparation of barium hexaferrite by a hydrothermal method: structure and magnetic properties

Barium hexaferrite, BaFe¹²O₁₉, was obtained in hydrothermal conditions from a water suspension of -FeOOH and Ba(OH)₂ · 8H₂O at a temperature about 315° C. X-ray and Mössbauer spectroscopy as well as electron microscopy investigations demonstrated the appearance of -Fe₂O₃ as an intermediate phase in the hydrothermal process. The magnetic characteristics of the obtained isotropic magnets are the following: coercive fieldH _c 159 kA m^–1, residual inductionB _r 0.26 T, maximum energy product (BH) _max12 kJ m^–3. The hydrothermal procedure for the preparation of barium hexaferrite in comparison with the conventional one is discussed.     

Effect of hydrothermal synthesis environment on the particle morphology,chemistry and magnetic properties of barium hexaferrite

Barium nitrate and iron nitrate have been used as precursors in the hydrothermal synthesis of barium hydroxide, iron oxide and barium hexaferrite sols under specified standard synthesis conditions (temperature, time, stirring, alkali concentration, amount of water and heating rate) as a function of the base species used during synthesis. The hydrothermal synthesis of barium hydroxide and iron oxide has been used to develop an understanding of the hydrothermal synthesis of barium hexaferrite from a mixture of their precursors. The investigation has shown that the nucleation and growth behaviour as well as the phase composition, thermal behaviour, particle size, particle-size distribution and magnetic properties are strong functions of the base species used. The electrostatic potential difference between the barium hydroxide and the iron oxide decreases with increasing cation size in the order NaOH, KOH, (C₂H₅)₄NOH and NH₄OH. Note the potential difference between the two sol species determines their tendency to coagulate into clusters; hence, the heterocoagulation will be greater when using NaOH or KOH than (C₂H₅)₄NOH or NH₄OH. Under the standard synthesis conditions, only NaOH and KOH are able to facilitate the formation of plate-like particles of barium hexaferrite. In contrast, ultrafine particles of iron oxide (10–20 nm) together with only a small amount of barium hexaferrite are produced when either NH₄OH or (C₂H₅)₄NOH base is used. The samples synthesized in the presence of the NaOH and KOH exhibit relatively higher saturation magnetization (i.e. 258 mT (39 e.m.u.g^–1) and 215 mT (32 e.m.u.g^–1), respectively) than those samples synthesized in the presence of NH₄OH or (C₂H₅)₄NOH which exhibit negligible saturation magnetization owing to the small amount of magnetic phase (BaFe₁₂O₁₉) present.     

Synthesis of barium hexaferrite for magnetic recording media using the KCl flux system

Individual and fine crystals of barium hexaferrite were prepared by a modified flux method using the KCI flux system. Co²⁺-Ti⁴⁺-substituted barium hexaferrite with a homogeneous composition was synthesized at 950° C for 5 h or at 1000° C for 1 h from a mixture of BaCO₃, Fe₂O₃, CoO and TiO₂ with 30 wt% KCI added. Laboratory-prepared fine Fe₂O₃, was preferred because it gave ferrite particles with diameters of 0.2 to 0.4m. Magnetic properties were controlled by the Co-Ti content in hexaferrite crystals. Coercive force and Curie temperature decreased with the degree of Co-Ti substitution with saturation magnetization held at high value. The present process, from which individual and fine barium hexaferrite crystals can be prepared by using the KCI flux system, is recommended as a means of mass-production of ferrite powders with controlled magnetic properties for use in magnetic recording media.     

Growth and properties of epitaxial barium hexaferrite films

Barium hexaferrite films have been grown by liquid phase epitaxy on Zr and Mg substituted Strontium hexagallate substrates. Continous films of 20 mm diameter have been obtained. The film surface exhibits terrace growth with a step height of about 10 nm. The saturation magnetization and anisotropy field as measured by static and FMR techniques are close to data of bulk crystals. An FMR linewidth of 45 Oe at 53 GHz was found for a 2.1 μm thick film.     

Influence of synthesis variables on the properties of barium hexaferrite nanoparticles

Barium hexaferrite (BaFe₁₂O₁₉) nanoparticles were synthesized by sol–gel auto-combustion route. Prepared samples were sintered at 950 and 1100 °C with Fe³⁺/Ba²⁺ = 12 and 20 mol ratio. The formation mechanism of barium hexaferrite was investigated by using X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses. In addition, the effect of temperature and Fe³⁺/Ba²⁺ mole ratio on BaFe₁₂O₁₉ formation and magnetic properties, and the effect of increasing the Fe³⁺/Ba²⁺ upon gel ignition and subsequent phase development were investigated. Finally the magnetic behavior was monitored with VSM. DSC studies showed that pure barium hexaferrite phase was formed from maghemite (γ-Fe₂O₃), without the formation of hematite (α-Fe₂O₃). Also, XRD results confirmed the formation of barium hexaferrite phase in non stoichiometric Fe/Ba ratio. VSM results showed that the saturation magnetization was decreased and coercivity increased with decreasing the grain size.     

纳米SrZnCo-W铁氧体的制备及磁性研究

以金属硝酸盐为原料,利用柠檬酸溶胶一凝胶自燃法制备出的SrZn2-xCoxFe16O27纳米六角铁氧体.利用XRD、TEM及VSM等对样品的粒径,分散性,物相组成及磁性能进行表征并讨论.结果表明,制备出的样品为单一的W型铁氧体,分散性良好,粒径在30～60nm;Sr-W铁氧体磁性能(饱和磁化强度Ms、剩余磁化强度Mr及内禀矫顽力Hc)随着Co含量的上升有不同的变化趋势,Ms、Mr及Hc分别在x=0.6、0.4与0.2时有最大值.     

Magnetic and dielectric properties of polycrystalline La doped barium Z-type hexaferrite for hyper-frequency applications

La³⁺ ion substituted barium Z-type hexaferrite, Ba_3?XLa_XCo₂Fe₂₄O₄₁ powders (X = 0.0, 0.05, 0.10 and 0.15), have been synthesized using sol gel auto-combustion method. The phase identification, microstructure, complex permittivity, complex permeability and static magnetic properties of the samples were studied using X-ray diffraction, scanning electron microscopy, vector network analyzer and vibrating sample magnetometer. The results revealed that introducing La³⁺ ion instead of Ba²⁺ ion led to an obvious enhancement of the electromagnetic properties. The crystallite size of the produced powders was slightly increased with increasing La³⁺ content. The microstructure of the produced powders appeared as hexagonal-platelet like structure. As the La content increase, the static magnetic properties were increased, the real part of complex permittivity was increased while the imaginary part was decreased. Moreover, the real part of complex magnetic permeability was decreased and the imaginary part was increased. The reasons of the obtained results were discussed on basis of electromagnetic theory.     

Synthesis, photoluminescence and magnetic properties of barium vanadate nanoflowers

The flower-shaped barium vanadate has been obtained by the composite hydroxide mediated (CHM) method from V₂O₅ and BaCl₂ at 200 °C for 13 h. XRD and XPS spectrum of the as-synthesized sample indicate it is hexagonal Ba₃V₂O₈ with small amount of Ba₃VO_4.8 coexistence. Scan electron microscope and transmission electron microscope display that the flower-shaped crystals are composed of nanosheets with thickness of ∼20 nm. The UV-visible spectrum shows that the barium vanadate sample has two optical gaps (3.85 eV and 3.12 eV). Photoluminescence spectrum of the barium vanadate flowers exhibits a visible light emission centered at 492 and 525 nm which might be attributed to VO₄ tetrahedron with T_d symmetry in Ba₃V₂O₈. The ferromagnetic behavior of the barium vanadate nanoflowers has been found with saturation magnetization of about 83.50 × 10⁻³ emu/g, coercivity of 18.89 Oe and remnant magnetization of 4.63 × 10⁻³ emu/g, which is mainly due to the presence of a non-orthovanadate phase with spin S = 1/2.     

Characterization of lead, barium and strontium leachability from foam glasses elaborated using waste cathode ray-tube glasses

Foam glass manufacture is a promising mode for re-using cathode ray tube (CRT) glasses. Nevertheless, because CRTs employ glasses containing heavy metals such as lead, barium and strontium, the leaching behaviour of foam glasses fabricated from CRTs must be understood. Using the AFNOR X 31-210 leaching assessment procedure, the degree of element inertization in foam glasses synthesized from waste CRT glasses (funnel and panel glasses, containing lead and barium/strontium respectively) were determined. The amount of leached lead from foam glasses prepared from funnel glass depends on the nature and concentration of the reducing agent. The effects of the reducing agents on the generation of cellular structure in the fabrication of foam glass were studied. The fraction of lead released from foam glass was less than those extracted from funnel glass and was lower than the statutory limit. Leached concentrations of barium and strontium were found to be approximately constant in various tests and were also below regulatory limits.     

Barium hexaferrite nanoparticles: morphology-controlled preparation,characterization and investigation of magnetic and photocatalytic properties

In this paper, barium hexaferrite (BaFe₁₂O₁₉) nanoparticles have been successfully synthesized via a simple co-precipitation route. Six chelating agents such as three amino acids (proline, alanine, aspartic acid) and three surfactants (SDBS, PVP, and EDTA) were used. The result showed that the amino acids decrease the particle size and the best result was observed for alanine. Besides, the photocatalyst activity of as-prepared BaFe₁₂O₁₉ nanoparticles was evaluated by degradation of methyl orange under visible light irradiation (λ?>?400 nm). The degradation rates of the methyl orange were measured to be as high as 95% in 200 min. The nanoparticles were also characterized by several techniques including FT-IR, XRD, SEM, and VSM. The VSM measurement showed a saturation magnetization value (Ms) of 30 emu/g.     

On the magnetic properties of fine-milled barium and strontium ferrite

The temperature dependence of the specific saturation magnetization of barium and strontium ferrite powders after milling in an attrition mill has been investigated at temperatures between -195°C and the Curie temperature of the ferrites. The experimental results show that the specific saturation magnetization decreases with increasing milling time and that a second, presumably soft-magnetic phase occurs during milling which vanishes during annealing of the powders. The influence of lattice defects introduced by the milling process is discussed.     

Physico-chemical, structural and physical properties of hydrogenated silicon oxinitride films elaborated by pulsed radiofrequency discharge

Films prepared by radiofrequency pulsed plasma enhanced chemical vapor deposition from a mixture of silane (SiH₄) and nitrous oxide (N₂O) were studied. Variation of operating conditions (flow rate, deposition temperature ...) resulted in films with chemical compositions changing from hydrogenated silicon oxynitride (SiO_xN_y:H) to silicon oxide (SiO_x:H). Infrared and Rutherford backscattering spectroscopy studies of the as-deposited films revealed different SiO_x arrangements disturbed by Si-N bonds and H-Si ≡ Si_(3 − x)O_x clusters depending on the substrate temperature and the N₂O/SiH₄ ratio. For films obtained using low N₂O/SiH₄ rations and annealed at temperature higher than 1273 K, Raman spectroscopy and microscopy analyses revealed the presence of silicon nanocrystals embedded in a matrix containing Si, O, and N. Spectroscopic ellipsometry revealed the presence of silicon nanocrystals along with two other amorphous phases (SiO_xN_y and SiO₂) in annealed samples. The electrical characteristics of annealed films obtained from capacitance-voltage measurements indicated a stable charge trapping in ultra-thin SiO_xN_y layers. These preliminary results suggest that Si-nc containing silicon oxynitride layers can be potential candidates to be used in the floating gate fabrication of memory devices.