Synthesis and Properties Investigation of Non-equivalent Substituted W-Type Hexaferrite

A novel composed W-type hexaferrite Ba_1?x La _x Co₂Fe₁₆O₂₇ was rapidly synthesized via a sol–gel self-combustion reaction. The effects of lanthanum ions on the oxidation state of iron ions and cobalt ions in hexaferrite were explored by X-ray photoelectron spectroscopy. The changes of the Fe 2p X-ray absorption spectra indicated that the nonequivalent substitution can lead to the transition Fe³⁺→ Fe²⁺ in Ba_1?x La _x Co₂Fe₁₆O₂₇. However, the oxidation state of cobalt ions was maintained as Co²⁺. Moreover, the effects of La content on the phase composition, structural parameters, morphology, and static magnetic properties were also investigated in detail by using the X-ray diffractometer, scanning electron microscope, and vibrating sample magnetometer. The results indicated that the structural parameters decreased regularly with increasing the La content, and the magnetic properties were enhanced after substitution, which is beneficial for their application in various electrical devices employed for industrial and military applications.     

Synthesis and Investigation of Electrical Properties of Strontium Metal-Doped Hexaferrite Nanoparticles

Journal of Superconductivity and Novel Magnetism - In the current work cobalt, magnesium and lithium dopant substitution is performed in series of SrFe(12-2x)(Co,Mg,Li)xO19 (for...     

Effect of Barium on the Properties of Lead Hexaferrite

An analysis of the properties of a family based on lead-barium substitution in the M-type hexaferrite is presented. The samples were prepared by the ceramic method according to the general formula Pb _x Ba_1?x Fe₁₂O₁₉. The barium content was varied with x=0.1, 0.3, 0.5, 0.7, and 0.9; no secondary phases were detected in any composition. Rietveld refinement analysis was done in order to determinate crystallographic parameters, content of phases and degree of substitution. The effects of the barium on the morphological and magnetic properties were studied. Iron Mössbauer spectroscopy was used for determining the hyperfine parameters of the iron nucleus and their environment; also, the cationic occupancy was evaluated and the results were checked with X-ray refinement results.     

Preparation and Magnetic Properties of La-Substituted Strontium Hexaferrite by Microwave-Assisted Sol-Gel Method

Sr_1?x La _x Fe₁₂O₁₉ (x = 0, 0.15, 0.25, 0.5) hexaferrites were prepared by microwave-assisted sol-gel method. The thermal decomposition process, structural, and magnetic properties of the products were studied by thermal differential scanning calorimeter (DSC), thermogravimetry (TG), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM). The phase of α-Fe₂O₃ appeared at x = 0.25 and x = 0.5. The coercivity of La³⁺-substituted strontium hexaferrites is improved to 5960.2 Oe at x = 0.25.     

Synthesis and Study of the Lanthanum Substitution in the Lead M-Type Hexaferrite

In this work we investigated the best conditions to obtain the lanthanum-substituted lead M-type hexaferrite using the ceramic method. In order to survey the solubility of lanthanum in the structure of the hexaferrite, we varied the molar fraction from 0.1 to 0.9. We performed a structural characterization using X-ray diffraction and used the Rietveld method to refine the crystal structure. The magnetic properties were obtained using vibrating sample magnetometry, and the microstructural characteristics were analyzed using scanning electron microscopy. The results indicate that the crystal structure of the hexaferrite is preserved with a substitution up to 70 %?mol of lanthanum. Moreover, the magnetic characterization exhibits a complicated behavior of parameters when lanthanum concentration increases, which can be attributed to the change of valence state of some iron cations that arises from lanthanum substitution in the hexaferrite; even more, the coercivity presents a drastic fall leading to consider these hexagonal ferrites as magnetically soft.     

Synthesis and Characterization of PEG-Sr Hexaferrite by Sol–Gel Conversion

Sr-M-type hexagonal ferrites have been prepared via a sol?Cgel route, and the effects of addition of different molecular weight polyethylene glycol (PEG) into the sol solutions on the static magnetic properties and particle morphology have been studied. Crystalline phases of the samples were determined by XRD analysis. FT-IR and TG analyses were used to prove the presence of PEG on SrFe₁₂O₁₉. The results showed that adding PEG with different molecular weight into the sol solutions affected the formation mechanism of SrFe₁₂O₁₉. Sr-M precursors prepared by various PEG types show different magnetic behaviors after pre-calcination at 150?^°C. This discrepancy is explained by the formation of a different phase during the synthesis of SrM particles.     

化学法制备的（Sr,Pb）TiO3基PTCR陶瓷

通过化学工艺制备（Ｓｒ，Ｐｂ）ＴｉＯ３半导体陶瓷，首次获得了与ＢａＴｉＯ３陶瓷相类似的典型ＰＴＣ特性，样品耐压强度大，室温电阻率低于１０＾２Ω．ｃｍ，升阻比高达１０＾６．３３，烧结温度可以降低至１１００℃以下。     

Synthesis and Characterization of Nano-crystalline Calcium Hexaferrite Particles by Mechano-Thermal Method

Calcium hexaferrite was synthesized using high-energy planetary ball milling of a mixture of CaCO₃ and Fe₂O₃ powders for 10 hours followed by calcination at 1175 ^°C for 1 h. Effects of Fe₂O₃/CaCO₃ molar ratio, mechanical activation and dopant addition on the phase evolution, morphology, and magnetic properties of the products were studied. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) technique equipped with an energy dispersive spectrometer (EDS), and vibrating sample magnetometer (VSM). XRD results showed that addition of La₂O₃ in the samples lead to the formation of stabilized calcium hexaferrite particles with a mean crystallite size of 54 nm. Moreover, the formation of calcium hexaferrite was acknowledged at Fe₂O₃/CaCO₃ molar ratio of 5. SEM micrographs showed agglomerated particles of calcium hexaferrite with a mean particle size of 1.5 μm. Nano-crystalline Ca_0.8La_0.2Fe₁₂O₁₆ particles show saturation magnetization of 14 emu/g and coercivity of 500 Oe.     

钡过量非化学计量M型铁氧体的合成与表征

采用并加共沉淀工艺在900℃热处理2h的条件下合成了单相钡过量非化学计量M型铁氧体Ba_1+xCoTiFe₁₀O_19+x(x=0.00、0.05、0.10、0.15、0.20), 并用XRD、SEM、TEM和VSM表征了这种新的非化学计量M型铁氧体的结构和磁学特性. 结果表明: 当0c和剩余磁化强度σ_r均随x增大而显著增大(Δσ_r=5.36A·m^2·kg^-1, ΔH_c=16.99 kA·m^-1, 但比饱和磁化强度σ_s基本不变; 0.053+离子被稀释导致σ_s、H_c和σ_r均随x增大而持续降低. 同时证实钡过量并不会导致晶体对称性破坏, 02+离子分布于平行于a轴方向的大孔隙位?置, 不仅具有助熔剂作用, 而且对磁畴壁产生了钉扎效应.     

Structure and Properties of Hard-Magnetic Barium, Strontium, and Lead Ferrites

The self-propagating high-temperature synthesis and sintering of Ba, Sr, and Pb ferrites are studied. The combustion temperature is shown to influence the defect density and internal stress in the resultant ferrite powders. The structure and properties of the ferrites are sensitive to both the combustion and sintering temperatures.     

M型锶铁氧体中空纤维的制备和表征

以柠檬酸和金属盐为原料,采用有机凝胶先驱体转化法制备了M型锶铁氧体（SrFe₁₂O₁₉）中空纤维. 通过FTIR、TG/DSC、XRD、SEM和VSM等技术对所得纤维进行了表征. 结果表明,凝胶的可纺性与其化学组成和pH值有关,当柠檬酸与金属离子的摩尔比为1.5∶1.0,pH=4.2左右时,凝胶的可纺性最好. 经1100℃焙烧后,制备的M型锶铁氧体中空纤维具有较大的长径比,直径可小于1μm,中空孔径约为纤维直径的一半,组成纤维的晶粒形貌为六角片状,晶粒尺寸为236nm,在室温下的饱和磁化强度为53.5A·m²/kg,矫顽力为386.96kA/m. 纤维显示出一定的形状各向异性,当定向排列的纤维平行和垂直磁场时,矫顽力分别为391.66和358.72kA/m.     

掺锶羟基磷灰石纳米颗粒的合成、表征及模拟研究

锶(Sr)掺杂羟基磷灰石(HA)在生物材料中得到广泛应用。在此研究中, 使用水热合成的方法制备HA和Sr掺杂HA的纳米颗粒。通过实验和计算机模拟的方法研究Sr掺杂对HA化学成分、结晶度、晶格参数、形貌和形成能的影响。实验结果表明, Sr掺杂后的HA纳米颗粒晶格参数和晶体尺寸增大。随着Sr离子浓度的增加, Sr 掺杂HA的纳米颗粒的结晶度没有显著变化。模拟结果验证了实验得到的Sr 掺杂HA纳米颗粒晶格参数的准确性, 且进一步表明Sr 离子掺杂后纳米颗粒的形成能较低, 结构更稳定。当Sr掺杂浓度为10%时, Sr掺杂的优先位点是Ca(1); Sr掺杂浓度为50%时, Sr混合掺杂到Ca(1)和Ca(2)位点为更优先的掺杂模式。     

BST组分梯度薄膜的性能研究

采用射频磁控溅射法在蓝宝石衬底上制备了上组分梯度、下组分梯度及单层BST薄膜,对比研究了三种结构BST薄膜的电、热性能.实验表明:下组分梯度BST薄膜的介电性能最优(优值因子为66.2),温度稳定性能最佳(在25～80℃范围内,介温变化率为7.8％).此外,实验还运用X射线衍射仪、场发射电子扫描显微镜和透射电子显微镜对BST薄膜的晶体结构进行了研究,运用EDS能谱仪对BST薄膜的组分梯度进行了验证.     

TiO2负载锶铁氧体磁性材料光催化性能及表征

采用溶胶-凝胶法合成了TiO₂负载锶铁氧体光催化剂, 通过XRD、TEM、UV-Vis、VSM等方法对催化剂结构进行了表征, 并以高压汞灯为光源, 亚甲基兰为目标降解物, 对其光催化活性进行了研究. 结果表明, TiO₂负载锶铁氧体为复合型光催化剂, 负载后的复合光催化剂保持了良好的磁性能; 锶铁氧体的负载拓宽了催化剂的光响应区域, 光吸收带进入可见光区; 在负载量为20％, 催化剂用量1.5g/L条件下, 催化降解亚甲基兰的效率可达99.1％.     

Preparation and Magnetic Properties of Nd3+, Al3+, Ca2+ Substituted M-Type Strontium Hexaferrites

Strontium ferrite with Nd³⁺, Al³⁺ and Ca²⁺ substitution of Fe³⁺ and Sr²⁺ ions were prepared by the conventional solid phase reaction process. The Nd³⁺ substitution shows 10 %–20 % improvement in coercivity for the substitution content less than 10 %. The Ca²⁺ substitution is favorable to the enhancement of saturation magnetization due to the accelerated reaction of Fe₂O₃ and SrCO₃. The samples with Al³⁺ substitution of Fe³⁺ show the lowest saturation magnetization, although the highest coercivity was achieved for a homogeneous grain size less than 1 μm. The combinatory substitution Nd³⁺, Ca²⁺ and Al³⁺ leads to the optimum magnetic properties with σ _s=52 A?m²/kg and H _cj=412 kA/m.     

新型铁电晶体铌镥酸铅-钛酸铅的生长与性能

采用顶部籽晶法生长了一系列不同组分的高居里温度铌镥酸铅-钛酸铅[(1-x)Pb(Lu_1/2Nb_1/2)O₃-xPbTiO₃ (PLN-xPT)]铁电晶体。该晶体在三方相区域表现出典型的介电弛豫特性, 不同组分的晶体表现出了较高的居里温度; 基于介电和结构测试结果, 得到了该体系的低温二元体系相图, 在相图中存在一个准同型相界区域(MPB), 其组分位于x = 0.49~0.51; 利用偏光显微镜分析晶体电畴结构得到和X射线粉末衍射测试结果吻合的相结构; 电学性能测试结果表明不同组分的晶体性能差异较大。组分位于MPB附近的晶体表现出优异的压电性能, 如x = 0.49时, 居里温度T_c = 360℃, 压电常数d₃₃ > 1600 pC/N。处于MPB附近的晶体存在较大的矫顽E_c >10kV/cm, 一些组分晶体的三方–四方相变温度T_RT > 200℃。结果表明高的居里温度及优异的压电性能使二元铌镥酸铅-钛酸铅晶体具有更大的温度应用范围及更广阔的应用前景。     

Synthesis and Characterization of T1-1223 Substituted by Scandium

X-ray powder diffraction, scanning electron microscopy （SEM）, energy dispersive X-ray, electrical resistivity and AC-magnetic susceptibility measurements have been performed for polycrystalline superconducting samples of type TIBa2Ca2_xSCxCU309_δ （0.0 ≤ x 〈 0.6）. The powder X-ray diffractograms indicate that the tetragonal structure of T1-1223 is not affected by Sc-substitution whereas the lattice parameters are changed. The X-ray analysis indicates that the low-contents of scandium （x） enhance the formation of T1-1223 and reduce the secondary phases. The grain-size determined by SEM decreases as x increases. The electrical resistivity measurements show suppression in the superconducting transition temperature, Tc, and an increase in both the residual resistivity and the superconducting transition width as x increases. The suppression in Tc is attributed to the hole-filling mechanism.