NiZn系软磁铁氧体材料的种类及应用

NiZn系软磁铁氧体是尖晶石铁氧体材料中的一个重要分支.NiZn系铁氧体材料以其电阻率高、烧结工艺简单、高频性能好等特点而获得广泛应用.本文简要介绍了当前应用前景较好的几类NiZn铁氧体材料及其应用,包括抗EMI系列铁氧体材料、射频宽带NiZn铁氧体材料、功率型NiZn系铁氧体材料和低温烧结NiCuZn铁氧体材料等,同时展望了各自的发展前景.     

Textured ferroelectric SrBi2Nb2O9 phase obtained by melt-quenching the SrBi2B2O7-Nb2O5 system and its anisotropic dielectric and pyroelectric properties

Textured SrBi₂Nb₂O₉ ceramics were obtained by quenching the melts of SrBi₂B₂O₇-Nb₂O₅ in equimolar ratio. The as-quenched samples were crystalline comprising 40% c-oriented grains. The influence of the post heat-treatment temperature on the orientation factor (f) and microstructure was studied using x-ray powder diffraction (XRD) and Scanning electron microscopy (SEM). The orientation factor was found to increase with increasing post heat-treatment temperature and reached a maximum value of 65% for the samples heated at 700°C for 10 h. Relative density and the grain-size of the partially grain oriented ceramics were found to increase with an increase in the heat-treatment temperature. The effect of texturing yielded anisotropy in the dielectric and pyroelectric properties. The dielectric constant ( e_r^￠ ( ^) = 114 ) \left( {\varepsilon_r^{\prime } \left( \bot \right) = 114} \right) and the pyroelectric coefficient (p(┴) = −0.07 nC cm⁻² °C⁻¹) along the direction perpendicular to the melt pressing axis were superior to that of the direction parallel ((e_r^￠ ( ||) = 93 \varepsilon_r^{\prime } \left( \parallel \right) = 93 ) (p(||) = −0.02 nC cm⁻² °C⁻¹)) (c-axis of the grain) to the pressing axis at room temperature.     

烧结温度对镍锌功率铁氧体磁性能的影响

为得到Zn含量不同时NiZn铁氧体材料的最佳烧结温度,用氧化物法制备了NiZn铁氧体材料,研究了烧结温度对材料起始磁导率、功耗、饱和磁感应强度和微结构的影响.结果表明,适宜的烧结温度对制备功耗低、饱和磁感应强度高和较优起始磁导率的NiZn铁氧体材料至关重要,而Zn含量不同时对应材料的最佳烧结温度也各不相同.     

The effect of Sb on the electrical and magnetic properties of Ni-Zn ferrites prepared by sol–gel autocombustion method

Polycrystalline Ni-Zn ferrites with a well-defined composition of Ni_0.4Zn_0.6Fe_2-xSb_xO₄ synthesized using sol–gel method. Morphological characterizations on the prepared samples were performed by high resolution transmission electron and field emission scanning electron microscopy. The powders were densified using microwave sintering method. The room temperature complex permittivity (ε′ and ε″) and permeability (μ′ and μ″) were measured over a wide frequency range from 1 MHz–1.8 GHz. The real part of permittivity varies as ‘x’ concentration increases and the resonance frequency was observed at much higher frequencies and there is a significant decrease in the loss factor (tanδ). The electrical resistivity and permeability of NiZn ferrites increased with an increase of Sb content. As the concentration of ‘x’ increases from 0 to 0.08 the saturation magnetisation decreases. The saturation magnetization (M_s)?≈?52.211 A.m²/Kg for x?=?0 at room temperature. The room temperature electro paramagnetic resonance (EPR) were studied.     

Integration of MnZn-ferrite tapes in LTCC multilayer

For co-firing of MnZn-ferrite tapes and LTCC dielectric tapes, the sintering shrinkage curves and the coefficient of thermal expansion of ferrite and dielectric tapes were matched. Highly densified embedded ferrite without any cracks could be manufactured by co-firing at 900 °C in nitrogen atmosphere. However, the permeability of MnZn-ferrite co-fired between dielectric tapes is significantly reduced (μ´=100) compared to that of the separately sintered ferrite (μ´=500). Changes in the phase stability and microstructure of MnZn-ferrite were investigated to explain the permeability reduction in the embedded ferrite. It is supposed that early densification of the dielectric tapes on the top and bottom of the ferrite layer prevent the gas exchange during sintering which is necessary for (Mn,Zn)Fe₂O₄ spinel formation. As a result, high amount of Fe₂O₃ secondary phase and a Mn-rich spinel phase with low permeability remain in the embedded ferrite layer.     

Effect of Co-substitution on the structure and magnetic properties of MnZn power ferrite

MnZn power ferrites with a composition of Mn_0.681-xZn_0.246Fe_2.073Co_xO₄ were prepared by conventional ceramic technique. The samples were sintered in a computer-driven furnace at 1320 °C for 4 h. Then the influences of Co-substitution on the crystalline structure, microstructure and the magnetic properties of MnZn power ferrite were studied. It shows that Co-substitution has not changed the structure of MnZn ferrite, but improved the crystallization. With the increase of Co substitution content, Co²⁺ ions firstly replace Mn²⁺ ions and then replace Fe³⁺ ions. And at room temperature, the initial permeability increases with the increase of Co-substitution content. Co-substitution can also reduce the porosity and the power loss. In addition, the corresponding temperature of the minimum power loss shifts to a lower temperature.     

Mg_(0.6)Cu_(0.1)Zn_(0.3)Fe_(2+x)O_(4+3/2x)铁氧体的结构和磁性能

分别采用过铁、正铁和缺铁配方通过固相反应法制备MgCuZn铁氧体,分析了Fe3+对铁氧体的磁性能和烧结特性的影响。微量缺铁有助于促进烧结并改善磁性能,过铁情况下,饱和磁化强度随x值增大迅速下降,在x=0.06处下降至38.84 A·m2/kg,相应的磁导率下降,截止频率向高频移动。并研究了微量V2O5掺杂对改善磁性能的作用,在掺杂量为0.4wt%处获得虚部损耗的有效提升(截止频率处提升近30%)。在此基础上探讨了MgCuZn铁氧体用作抗EMI磁珠的可行性,其低廉的价格相较于传统的Ni Zn/Ni Cu Zn铁氧体具有明显的优势。     

Co2O3或/和V2O5掺杂对NiZn铁氧体磁性能的影响

一定量的V2O5掺杂有利于NiZn铁氧体烧结温度的降低，且在一定范围内起始磁导率升高；而Co2O3掺于Nizn铁氧体，起始磁导率降低，但损耗特性可得到改善。我们采用Co2O3-V2O5复合掺杂，发现选择适当的配比，在起始磁导率没有大的下降的情况下，烧结温度和损耗特性等其他磁特性可得到较好的改善。     

Preparation, thermal stability and permeability behavior of substituted Z-type hexagonal ferrites for multilayer inductors

Co₂Z-type hexagonal ferrites with iron excess Ba₃Co_2???x Fe_24?+?x O₄₁ (0?≤?x?≤?0.8) and deficiency Ba₃Co_2?+?y Fe_24???y O₄₁ (0?≤?y?≤?0.6) were prepared by an oxalate coprecipitation technique. This synthesis route leads to almost single phase Z-type ferrites for x?=?0 after calcination and sintering at 1330 °C. The Z-type formation is enhanced for x?>?0 and single phase ferrites are obtained for 0.4?≤?x?≤?0.8. The permeability of Z-type ferrites varies with composition x: Maximum permeability of μ′?=?28 is observed for 0.4?≤?x?≤?0.6 for samples sintered at 1330 °C. The frequency dispersion shows broad peaks of μ″ stretching from 200 MHz to >1 GHz. For iron deficient samples 0?≤?y?≤?0.6 multi-phase mixtures were obtained. For Ag-based multilayer inductor applications sintering at 950 °C is required. Co₂Z ferrites with Fe excess are not stable at this temperature as demonstrated by XRD. The permeability of samples sintered at 950 °C is drastically reduced to μ′?=?3. This demonstrates that these materials are not able to provide sufficient permeability for multilayer inductors for high-frequency operations since they are not compatible with the low temperature ceramic cofiring technology.     

Microstructural and electrical properties of multicomponent varistor ceramics with PbO–ZnO–B2O3 glass addition

Zinc oxide based ceramics are widely used materials in varistors because of their excellent nonlinearity. Traditionally these ceramics are sintered at high temperatures (about 1,100–1,300°C). In this work a novel zinc oxide-based material with a low sintering temperature (900–1,000°C) was investigated. This material can be used in varistors consisting of several ceramic layers with embedded silver/palladium thick-film electrodes. This paper explains the research procedure employed with this novel varistor material, including the effect of sintering aid addition on the final electrical properties and fired microstructure. The electrical properties achieved are compared to the values measured from the original zinc oxide composition without sintering aid addition. Especially the I–V characteristics, nonlinearity coefficient α, breakdown voltage V _bk and leakage current density J _L are investigated. The sintering properties are also reported. It was found that by adding 10 wt.% of glass and using a 900 °C sintering temperature, the material had good varistor characteristics, as V _bk = 378 V/mm, α = 33 and J _L  = 15 μA/cm². The investigated varistor material can be applied to protect electrical circuits against surges.     

Ni-Cu-Zn Ferrites for Low Temperature Firing: I. Ferrite Composition and its Effect on Sintering Behavior and Permeability

Ni-Cu-Zn ferrites of composition Ni_{1 − x − y}Cu_yZn_xFe₂O₄ with 0.4 ≰ x ≰ 0.6 and 0 ≰ y ≰ 0.25 were prepared by standard ceramic processing routes. The density of samples sintered at 900^∘C increases with copper concentration y. Dilatometry reveals a significant decrease of the temperature of maximum shrinkage with y. The permeability has maximum values of μ = 500–1000 for x = 0.6. The Curie temperature is sensitive to composition and changes form about 150^∘C for x = 0.6 to T_c > 250^∘C for x = 0.4, almost independent on the Cu-content. A small iron deficiency in Ni_0.20Cu_0.20Zn_{0.60 + z}Fe_{2 − z}O_{4 − (z/2)} with 0 ≰ z ≰ 0.06 significantly enhances the density of samples sintered at 900^∘C. The maximum shrinkage rate is shifted to T < 900^∘C. These compositions are therefore appropriate for application in low temperature co-firing processes. The permeability is reduced with z, hence a small z = 0.02 seems to be the optimum ferrite composition for high sintering activity and permeability.     

Ni-Cu-Zn Ferrites for low temperature firing: II. Effects of powder morphology and Bi2O3 addition on microstructure and permeability

The morphology of Ni-Cu-Zn ferrite powders obtained by milling of a calcined raw materials mixture strongly effects the densification behavior during sintering at 900^∘C. In order to obtain dense samples sub-micron powders with enhanced reactivity are required. The addition of Bi₂O₃ as sintering additive is beneficial: the density of samples sintered at 900^∘C increases with the bismuth oxide concentration up to 0.75 wt.%. The process of liquid phase sintering was studied by dilatometry. The grain size of the sintered samples slightly increases for 0.25 wt.% Bi₂O₃ compared to bismuth-free samples, whereas for 0.3–0.5 wt.% Bi₂O₃ additions bimodal grain growth is observed with a significant fraction of very large grains. For > 0.5 wt.% Bi₂O₃ a homogeneous coarse-grained microstructure is obtained. The permeability increases for small bismuth oxide additions, but decreases for a Bi-oxide content of more than 0.5%. Maximum permeability of μ_i = 900 is observed for intermediate Bi₂O₃ concentrations. PACS codes: 75.50 Gg; 81.20 Ev; 81.40 Rs     

用纳米粉料制作块状NiZn铁氧体材料的研究

采用化学共沉法制备纳米NiZn铁氧体粉料，由纳米粉料制备了块状NiZn铁氧体．研究了配方和烧结温度对铁氧体性能的影响。     

Investigations of lanthanum doping on magnetic properties of nano cobalt ferrites

The magnetic properties of nano-crystallite cobalt lanthanum ferrite (CoLa_xFe_2-x O₄) with varied quantities of lanthanum (x = 0, 0.1, 0.15, 0.2, 0.25, 0.3) prepared by co-precipitation method have been studied by vibrating sample magnetometer (VSM) and LCR meter. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the size, structure, and morphology of the ferrite samples. The average crystallite size varied from 17.83 nm to 49.99 nm. All the samples, although, in nano range, show significant hysteresis. The saturation magnetization (M_s) values decreased from 60.57 emu/g to 30.15 emu/g. The remanence (M_R) fell from 10.85 emu/g to 6.39 emu/g. Doping with lanthanum La³⁺ ions modulates significantly the magnetic properties of cobalt spinel ferrites without sacrificing the ferromagnetic character.     

Microwave-Hydrothermal Synthesis of Ni0.53Cu0.12Zn0.35Fe2O4/SiO2 Nanocomposites for MLCI

The nanocomposites of NiCuZnFe₂O₄-SiO₂ were prepared using Microwave-Hydrothermal method at 160°C/45 min.The as-synthesized powders were characterized using X-ray diffraction and Transmission Electron Microscope (TEM).The average particle size of the powders were found to be ～20 nm.The powders were densified at 900°C/30 min using Microwave sintering method. The sintered composite samples were characterized using XRD and Scanning Electron Microscopy (SEM). Crystallite size of the ferrites decreases with an increase of SiO₂ content. The density of the composites varies of 93–98% of theoretical density. The densities of the present composites were increasing with the addition of SiO_2. The bulk densities of the present composites were increasing with the addition of SiO₂. The structural changes in these samples were characterized using Fourier Transform Infrared Spectrometer (FTIR) in the 400–4000 cm^?1. The bands in the range of 580–880 cm^?1 show a slight increase in intensity, which could be ascribed to the enhanced interactions between the NiCuZnFe₂O₄ clusters and silica matrix. The resistivity of the sintered samples was increased with an addition of ferrite content. The real and imaginary parts of permittivity and permeability were measured in the frequency range of 1 MHz–1.8 GHz.The addition of SiO₂ alters the values of dielectric constant and permeability which is useful to the Multilayer Chip Inductors (MLCI) fabrication.     

Ni–Mn–Fe–Cr–O negative temperature coefficient thermistor compositions: Correlation between processing conditions and electrical characteristics

A study has been carried out to correlate the effect of sintering temperature on the microstructural, electrical and reliability aspects of Ni_0.75Mn_{(2.25−x−y)}Cr _x Fe _y O₄ (x = 0 to 0.3 and y = 0 to 0.3) negative temperature coefficient thermistor compositions prepared by solid-state route. The calcined and sintered compositions were characterized by X-ray diffraction and Scanning Electron Microscopy. The existence of cubic spinel single-phase region was determined by sintering Ni_0.75Mn_{(2.25−x−y)}Cr _x Fe _y O₄ samples in air at temperatures 1150 to 1250 °C. X-ray diffraction patterns of samples sintered above 1200 °C shows additional Bragg reflections of a rock salt structured NiO phase besides normal cubic spinel. A maximum B-value of 4044 K was obtained for Ni_0.75Mn_1.95Cr_0.25Fe_0.05O₄ composition at a sintering temperature 1250 °C/3 h. The reliability of the thermistor compositions were evaluated by performing accelerated ageing based on thermal cycling test. We found that chromium enhances the reliability of Ni_0.75Mn_{(2.25−x−y)}Cr _x Fe _y O₄ (x = 0 to 0.3 and y = 0 to 0.3) based NTC thermistor compositions. A maximum reliability of +0.25% resistance drift was observed at sintering temperature 1200 °C for 0.25 mol% chromium content. Excellent reliability of Ni_0.75Mn_{(2.25−x−y)}Cr _x Fe _y O₄ NTC thermistor compositions makes it ideal candidates for high-performance thermal sensor applications.     

射频宽带LTN_2B NiZn铁氧体材料的研制与特性

采用传统氧化物工艺结合复合掺杂制备Ni_xZn_(1-x)Fe_2O_4铁氧体材料,采用适当的技术措施优化工艺.根据磁导率和居里温度随锌含量的变化,确定出满足设计指标要求的成分x=0.36,选择合理的烧结温度,制备出综合性能较优、牌号为LTN2B的优质镍锌铁氧体材料, 达到了设计指标.其起始磁导率μ_i为2188、居里温度T_C为136℃、饱和磁感应强度B_s为319 mT,可望应用于射频宽带抗EMI滤波器.     

宽温高磁导率软磁铁氧体材料RH15K的开发

采用传统氧化物陶瓷工艺制备锰锌铁氧体,研究了主配方的氧化铁含量、烧结工艺等因素对材料微观结构和磁导率的影响。结果表明,主配方氧化铁含量在52.2 mol%时,可以获得较好的磁导率温度特性;烧结温度1380℃,保温8~12 h,有助于提高起始磁导率;晶粒直径25μm左右和致密的微观结构,可提高材料的起始磁导率。通过优化配方和制备工艺,开发出了宽温、高磁导率锰锌铁氧体材料RH15K,性能如下:起始磁导率μi:15000±30%(25℃,10 k Hz),μi5000(-40℃,10 k Hz),居里温度TC105℃。     

Ni0.25Zn0.15Fe2.6O4种子层对NiZn铁氧体双层膜性能的影响

采用旋转喷涂法在Si(100)基片上制备Ni0.25Zn0.15Fe2.6O4(100 nm)铁氧体薄膜作为种子层,然后在种子层上采用射频磁控溅射法沉积Ni0.25Cu0.09Zn0.66Fe1.998O4(600 nm)铁氧体薄膜。研究了种子层对NiZn铁氧体双层膜微观形貌、饱和磁化强度、矫顽力、磁导率及截止频率的影响。结果表明,Ni0.25Zn0.15Fe2.6O4种子层的引入促进了NiZn铁氧体双层膜尖晶石相的晶化和晶粒生长。NiZn铁氧体双层膜的饱和磁化强度Ms为420 kA/m,矫顽力Hc为5.9kA/m,截止频率fr为1.37 GHz,磁导率μ’(300 MHz)高达202。     

Complex permittivity and permeability of Co-substituted NiCuZn ferrite at rf and microwave frequencies

NiCuZn ferrite has recently attracted a lot of attention for its application in high frequency (up to a few GHz) multilayer chip inductors (MLCIs) and for other microwave devices owing to their favorable electromagnetic properties and low densification temperature. In order to study the effect of substitution of cations by cobalt in small concentration on the dielectric and magnetic properties at low and high frequencies, bulk polycrystalline ferrite samples of starting composition (Ni_0.2Cu_0.2Zn_0.6)_{1 − x} Co _x Fe₂O₄, having x = 0, 0.01, 0.03 and 0.05, were prepared by citrate precursor method. Pure spinel (cubic) ferrite formation was confirmed by powder X-ray diffraction technique. Complex permittivity and permeability were measured at microwave frequencies (X-band) using the cavity perturbation method, which is a non-contact method. The values of real part of permittivity (ε ′) vary in the range 7–9.6 and of the imaginary part (ε ″) vary from 0.020–0.120, whereas real part of the permeability (μ′) lies in the range 2.6–14.0 and the imaginary part of permeability (μ″) varies from 0.5–6.0. It is observed that there is an increase in μ′ and decrease in the magnetic loss (tan δ _μ) on increasing the cobalt concentration from x = 0 to x = 0.05. The variation of these parameters, both with frequency in X-band and with the cobalt concentration, is discussed in this paper.