Co2+对CoxFe3-xO4铁氧体结构与磁特性的影响

采用化学共沉法制备了纳米尺度的钴铁氧体CoxFe3-xO4（x=0．2～1．0）粉料,并在1260—1340℃温度下进行了退火处理,利用X射线衍射仪（XRD）、振动样品磁强计（VSM）对样品的结构和磁性进行了测量和分析。实验结果表明,当钴含量高（x≥0．7）时样品形成了单一的具有尖晶石结构的钴铁氧体,而钴含量x〈0．7时样品生成了尖晶石结构的钴铁氧体相和仪α-Fe2O3相CoxFe3-xO4的比饱和磁化强度σs随x的增加呈现出了先增后减的趋势,在x=0．8时出现峰值;x=0．5～0．8范围内,矫顽力日。随钴含量的增加有所下降,随后迅速增加,在x=1．0附近能同时得到较大的σs和Hc值。     

自燃/球磨法制备NiZn系铁氧体

以金属硝酸盐和柠檬酸为原料,用溶胶凝胶自燃烧法制备NiZn系铁氧体前驱体粉末(Ni0.4Zn0.6Fe2O4,Ni0.2Zn0.6Cu0.2Fe2O4,Ni0.33Zn0.59Cu0.11Fe1.97O4(Bi2O3)0.002和Ni0.33Zn0.59Cu0.11 Fe1.97O4(Bi2O3)0.002(MnO2)0.02),然后经30小时高能球磨,从X-ray衍射谱中发现前驱体粉末虽然基本上是尖晶石结构,但是还有一些杂相,经过球磨,杂相明显减少,结构更加完整,颗粒减小.前驱体粉末Ni0.33Zn0.59Cu0.11Fe1.97O4(Bi2O3)0.002经30小时球磨后,在空气中退火,退火温度分别为400℃,600℃,800℃,900℃,1000℃.用X-ray衍射谱分析其物相,发现在800℃退火得到单相的尖晶石结构,无杂相.该样品的最佳退火温度低于1000℃.用振动样品磁强计分别测量制备态和退火态样品粉末的磁性,可以看出,随退火温度的升高,比饱和磁化强度σs逐渐增大,矫顽力Hc逐渐减小,当900℃退火后,比饱和磁化强度已接近块状NiZn系铁氧体.1000℃退火后,上述四种样品中Ni0.4Zn0.6Fe2O4具有最高的比饱和磁化强度σs=65.09emu/g.本文为NiZn铁氧体的低温烧结提供了有用的实验数据.     

纳米晶 Ni1-x ZnxFe2O4铁氧体粉料的制备及其磁性能研究

采用喷射-共沉淀法制备了纳米晶Ni1-xZnxFe2O4（0≤x≤1.0）铁氧体粉料.通过TG-DSC、XRD、SEM、TEM、BET等测试手段分析了其微观结构和形貌,用振动样品磁强计测量其室温下磁性能.结果表明：喷射-共沉淀法制备的粉料颗粒细小均匀、形状完整.600℃下煅烧1.5h,样品晶粒尺寸为30nm左右,平均颗粒尺寸＜100nm.室温下,样品比饱和磁化强度随Zn^2＋含量增加而变化,当x=0.5时,最大比饱和磁化强度σs为66.8A·m^2/kg.当晶粒大小为41nm时,纳米晶Ni0.5Zn0.5Fe2O4铁氧体矫顽力达到最大值5.06kA/m,随后又随晶粒尺寸增大而减小.这归因于纳米晶软磁材料中强烈的无序磁晶各向异性模式的影响.     

微波多元醇法制备单分散Ni1-xZnxFe2O4/MWCNTs与磁性能

以多壁碳纳米管(MWCNTs)为模板,三乙二醇(TREG)为溶剂,采用微波多元醇法制备MWC-NTs负载组成可控的Ni1-xZnxFe2O4(x=0.4、0.5、0.6)纳米复合材料Ni1-xZnxFe2O4/MWCNTs。其结构和形貌通过XRD、SEM、TEM和EDX进行表征,用VSM测试样品的磁性,并探讨了微波功率、微波时间对镍锌铁氧体负载的影响。结果表明立方系尖晶石结构的单分散Ni1-xZnxFe2O4磁性纳米粒子均匀负载在碳纳米管表面,平均粒径约为6nm;其磁性能与镍锌铁氧体的组成有关,随着Zn含量的增加,饱和磁化强度(Ms)先增大后减小,当x=0.5时Ms达到最大值。矫顽力(Hc)都比较小,在室温下表现为超顺磁性。     

锰锌铁氧体纳米粒子的制备和磁性能研究

以金属离子的硫酸盐溶液和氨水溶液为原料,采用水热法制备了粒径为6～16nm的锰锌铁氧体纳米粒子.采用XRD、TEM、TGA和VSM等方法对产物以及产物的磁性能进行了表征.结果表明,锰锌铁氧体(Mn1-xZnxFe2O4)的居里温度随着锌的相对含量x的增加而单调的降低.锰锌铁氧体的磁化强度先随着锌的相对含量x的增加而增大,当锌的相对含量＞0.6时,磁化强度随着锌的相对含量x的增加而减小.测量了锰锌铁氧体磁流体的饱和磁化强度,计算了锰锌铁氧体(Mn0.4Zn0.6Fe2O4)纳米粒子的磁矩,其值为1.01×10-19A·m2.     

不同表面处理剂对M型掺杂锶铁氧体(SiLaxFe12-xO19（x=0.5）)/聚吡咯（PPy）的吸波性能影响分析

采用溶胶-凝胶法及脱脂棉作为模板制得絮状掺杂锶铁氧体(SiLaxFe12-xO19(x=0.5)),通过引入不同种类表面活性剂,制备出M型掺杂锶铁氧体(SiLaxFe12-xO19(x=0.5))/聚吡咯(PPy)复合吸波材料。结果表明:采用表面活性剂十二烷基苯磺酸钠(C18H29NaO3S)合成的吸波材料的饱和磁化强度(emu/g)、矫顽力(Oe)及剩余磁化强度(emu/g)要高于使用阳离子表面活性剂。γ-甲基丙烯酰氧基丙基三甲氧基硅烷(KH-570)合成的吸波材料磁化性能明显优于阴/阳离子表面活性剂,但阴/阳离子表面活性剂磁损耗比较高。最佳频率匹配范围为800~1000MHz。     

不同表面处理剂对M型掺杂锶铁氧体(SiLaxFe12-xO19（x=0.5）)/聚吡咯（PPy）的吸波性能影响分析

采用溶胶-凝胶法及脱脂棉作为模板制得絮状掺杂锶铁氧体(SiLaxFe12-xO19(x=0.5)),通过引入不同种类表面活性剂,制备出M型掺杂锶铁氧体(SiLaxFe12-xO19(x=0.5))/聚吡咯(PPy)复合吸波材料。结果表明:采用表面活性剂十二烷基苯磺酸钠(C18H29NaO3S)合成的吸波材料的饱和磁化强度(emu/g)、矫顽力(Oe)及剩余磁化强度(emu/g)要高于使用阳离子表面活性剂。γ-甲基丙烯酰氧基丙基三甲氧基硅烷(KH-570)合成的吸波材料磁化性能明显优于阴/阳离子表面活性剂,但阴/阳离子表面活性剂磁损耗比较高。最佳频率匹配范围为800~1000MHz。     

Zn2+含量对纳米Ni-Zn铁氧体结构和磁性能的影响

采用喷射-沉淀法成功地制备了纳米晶Ni1-xZnxFe2O4(0≤x≤1.0)铁氧体粉料。通过TG-DSC,XRD,TEM等测试手段分析了其微观结构和形貌,用振动样品磁强计测量其室温下磁性能。结果表明:喷射-共沉淀法制备的粉料颗粒细小均匀、形状完整。600℃下煅烧1.5h,样品晶粒尺寸为30nm左右,平均颗粒尺寸小于100nm。随着Zn2+含量的增加,Ni-Zn铁氧体的晶胞参数逐渐增大。室温下,样品比饱和磁化强度随Zn2+含量增加而增加,当x=0.5mol时,最大比饱和磁化强度Ms为66.8A.m2.kg-1。     

马尾松边材基Sr1-xLaxFe12-xCoxO19铁氧体制备及磁性

以马尾松边材为模板,用sol-gel法制备出多层壁结构Sr1-xLaxFe12-xCoxO19(x=0～0.2)铁氧体样品。利用XRD、SEM、VSM对样品的结构、形貌、磁性进行了表征。结果表明锶铁氧体保留了木材的多层壁结构,壁厚约1～2μm,锶铁氧体微粒尺寸约在1～1.5μm,每个微粒水平连接构成管胞壁。样品的饱和磁化强度随x值增大而增加,矫顽力则随着x值增大先增大后减小。但平行壁方向(A方向)的矫顽力明显低于其它方向(B、C方向)。     

黄钠铁矾渣制备镍锌铁氧体及其表征

利用化学共沉淀法,以黄钠铁矾渣为原料制备镍锌铁氧体。以正丁胺为沉淀剂,在室温条件下,通过共沉淀铁、镍、锌(镍、锌由硫酸锌、硫酸镍按Ni0.5Zn0.5Fe2O4比例补加)制备镍锌铁氧体样品。采用SEM、XRD和FT-IR对该样品进行表征。结果表明,制备所得的样品为镍锌铁氧体。同时,通过磁滞回线显示,镍锌铁氧体比饱和磁化强度为9.04A·m2/kg,比剩余磁化强度为0.65 A·m2/kg,矫顽力为2.47kA/m,具有软磁材料的低比剩余磁化强度和低矫顽力的特性。     

Varistor properties of ZnO-Pr6O11-CoO-Cr2O3-Y2O3-In2O3 ceramics

The varistor properties of the ZnO-Pr₆O₁₁-CoO-Cr₂O₃-Y₂O₃-In₂O₃ ceramics were investigated for different concentrations of In₂O₃. The increase of In₂O₃ concentration slightly increased the sintered density (5.60-5.63 g/cm³) and slightly decreased the average grain size (3.4-2.9 μm). The breakdown field increased from 6023 to 14822 V/cm with increasing concentration of In₂O₃. The nonlinear coefficient increased from 17.6 to 44.6 for up to 0.005 mol%, whereas the further doping caused it to decrease to 36.8. In₂O₃ acted as an acceptor due to the donor concentration, which decreases in the range of 1.02 × 10¹⁷ to 0.24 × 10¹⁷/cm³ with increasing concentration of In₂O₃.     

Nanocrystallization of SrBi2Nb2O9 from glasses in the system Li2B4O7---SrO---Bi2O3---Nb2O5

Transparent glasses in the system (100−x)Li₂B₄O₇–x(SrO---Bi₂O₃---Nb₂O₅) (10≤x≤60) (in molar ratio) were fabricated by a conventional melt-quenching technique. Amorphous and glassy characteristics of the as-quenched samples were established via X-ray powder diffraction (XRD) and differential thermal analyses (DTA) respectively. Glass–ceramics embedded with strontium bismuth niobate, SrBi₂Nb₂O₉ (SBN) nanocrystals were produced by heat-treating the as-quenched glasses at temperatures higher than 500 °C. Perovskite SBN phase formation through an intermediate fluorite phase in the glass matrix was confirmed by XRD and transmission electron microscopy (TEM). Infrared and Raman spectroscopic studies corroborate the observation of fluorite phase formation. The dielectric constant (_r) and the loss factor (D) for the lithium borate, Li₂B₄O₇ (LBO) glass comprising randomly oriented SBN nanocrystals were determined and compared with those predicted based on the various dielectric mixture rule formalism. The dielectric constant was found to increase with increasing SBN content in LBO glass matrix.     

Characterization of YBa2Cu3O7/PrBa2Cu3O7 superlattices

We investigated the structural and superconducting properties ofc-axis oriented (YBa₂Cu₃O₇) _nY /(PrBa₂Cu₃O₇) _npr superlattices with thicknesses of the individual layers down to one unit cell (10nY1; 18>nPr 1). By transmission electron microscopy and X-ray diffraction we find an excellent structural quality of the samples, though the quantitative analysis shows the existence of defects. In superlattices with decoupled YBa₂Cu₃O₇ layers of two unit cell thickness we find a highT _c value of 75 K. We probed the flux line structure in the superlattices by measurements of the critical current density in magnetic fields. The experiments show that the flux-line dynamics is dominated by the movement of pancake vortices.     

Syntheses of hollandite type Rb2Cr8O16, K2Cr2V6O16 and K2V8O16

Hollandite-type compounds, Rb₂Cr₈O₁₆, K₂Cr₂V₆O₁₆ and K₂V₈O₁₆, were synthesized under high P-T conditions up to 1200°C and 7GPa. The structural refinement using a single crystal of Rb₂Cr₈O₁₆ confirms that the structure is similar to that of K₂Cr₈O₁₆. Magnetic measurements indicate that Rb₂Cr₈O₁₆ is ferromagnetic below 295K, K₂Cr₂V₆O₁₆ paramagnetic down to 77K and K₂V₈O₁₆ has susceptibility anomaly at 175K. These compounds are all semiconductive and show discontinuities in temperature-resistivity curves at points corresponding to magnetic anomalies.     

Magnetic coupling in La0.67Ca0.33MnO3/La0.67Sr0.33CoO3/La0.67Ca0.33MnO3 sandwiches

La_0.67Ca_0.33MnO₃ (LCMO)/La_0.67Sr_0.33CoO₃ (LSCO)/LCMO trilayer films are fabricated on single-crystal substrates NdGaO₃ (110) and the interlayer coupling are investigated. Compared with LCMO single layer, sandwiches showed the enhanced metal-insulator transition temperature of LCMO layers. The magnetoresistance is dependent on spacer thickness and the peak value dramatically decreases when LSCO layer is thick enough because of shorting by the LSCO layer. The magnetic coercivity H_C shows a nonmonotonic behavior with changing spacer layer thickness and the waist-like hysteresis indicates that there is an indirect exchange coupling between the top and bottom LCMO layers across the spacer layer.     

The effect of Bi1.5Zn0.5Nb0.5Ti1.5O7 cover layer on the dielectric and tunable properties of Ba0.6Sr0.4TiO3/Bi1.5Zn0.5Nb0.5Ti1.5O7 bilayered thin films

Bi_1.5Zn_0.5Nb_0.5Ti_1.5O₇ (BZNT) thin films with different thicknesses as cover layers were deposited on the Ba_0.6Sr_0.4TiO₃ (BST) thin films on the Pt/Ti/SiO₂/Si substrates by radio frequency magnetron sputtering method. The microstructure, surface morphology, dielectric and tunable properties of BST/BZNT heterogeneous bilayered films were investigated as a function of the thickness of BZNT films and the effect of BZNT films on the asymmetric electrical properties of BST/BZNT bilayered films was discussed. It was found that BZNT cover layer significantly improved the leakage current and the dielectric loss, and the dielectric constant and tunability of BST/BZNT bilayered thin films simultaneously decreased with the increasing thickness of BZNT films. The BST/BZNT bilayered thin film with a 50 nm BZNT cover layer gave the largest figure of merit (FOM) of 33.48 with the upper tunability of 55.38%. The asymmetric electrical behavior of BST/BZNT bilayered films is probably related to an internal electric field caused by built-in voltages at Pt/BST and BZNT/Au interfaces.     

MoO3-V2O5-P2O5-Fe2O3玻璃的制备及性能研究

制备了MoO3-V2O5-P2O5-Fe2O3系磷酸盐玻璃,研究了玻璃形成能力、热膨胀系数和抗潮解等性能.结果表明,MoO3-V2O5-P2O5-Fe2O3系统具有较宽的玻璃形成区和较强的玻璃形成能力,当MoO3/V2O5≈1.5时,玻璃形成能力最强.MoO3-V2O5-P2O5-Fe2O3玻璃的热膨胀系数约为60～110×10-7/℃,并且随着Fe2O3含量的增加而逐渐增大.加入适量的Fe2O3能够显著改善MoO3-V2O5-P2O5玻璃的抗潮解性能,在90℃的去离子水中的溶解速率达到8.0×10-9g·cm-2·min-1.     

Structural study of Sr0.3Ba0.7Nb2O6 and La0.030Sr0.255Ba0.700Nb2O6 ceramic systems

Sr_0.3Ba_0.7Nb₂O₆ (SBN) and La_0.030Sr_0.255Ba_0.700Nb₂O₆ (LSBN) ceramic compounds have been prepared using the traditional ceramic method at two different calcination temperatures (900 and 1000 °C) and later sintered both at 1400 °C. A study of the effects of the calcination temperatures and La substitution on the morphological, compositional, and structural properties of SBN and LSBN is presented using scanning electronic microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analysis. From Rietveld refinement processes, the XRD patterns were interpreted to evaluate such effects in the structural parameters and the site occupation factors of the heavy metals and oxygen atoms. The effect of the incorporation of La resulted in a 0.25% cell contraction and turned out to be higher than the 0.08% dilation effect produced by the increase of calcination temperature. The La ion with similar effective ionic radius and higher electronegativity is incorporated into the structure occupying the A₁ site just like the Sr ions in the SBN compound. Differences in the site occupation factors between the SBN and LSBN samples lead to substantial changes in the physical properties such as temperature of relative dielectric constant maximum, relative dielectric constant, and dielectric loss, correlated with the distortion and the relative orientation of the oxygen octahedra.     

Microstructures of YBa2Cu3O7/La0.7Ca0.3MnO3 and La0.7Ca0.3MnO3/YBa2Cu3O7 bi-layers grown on (001)LaAlO3

Epitaxial YBa₂Cu₃O₇/La_0.7Ca_0.3MnO₃ (YBCO/LCMO) bi-layers and La_0.7Ca_0.3MnO₃/YBa₂Cu₃O₇ (LCMO/YBCO) bi-layers were grown on (001)LaAlO₃ by pulsed laser deposition, and their microstructures were compared by transmission electron microscopy investigation. In the YBCO(100 nm)/LCMO(150 nm) bi-layers, the LCMO layer consists of columnar grains of ~ 17 nm in diameter and contains mixed orientation domains of [100]_c, [010]_c and [001]_c. The YBCO layer is totally c-axis oriented and the YBCO lattices are tilted − 2.5° to + 2.5° as they grew on the rough surfaces of LCMO columnar grains. For the LCMO(140 nm)/YBCO(140 nm) bi-layers, the LCMO/YBCO interface is sharp and flat. The initial 12-nm thickness of the YBCO layer is composed of c-axis oriented domains, and the upper part of YBCO layer is [100] oriented. The LCMO layer was predominantly [001]_c oriented while [100]_c-oriented domains were occasionally observed.     

MgO-Al2O3-SiO2-TiO2-Y2O3玻璃的弹性模量

根据硬盘基板用材料的要求，制备了MgO-Al2O3-SiO2-TiO2-Y2O3高弹性模量玻璃（120GPa)，玻璃的弹性模量随组成的变化服从Makishima-Mackenzie理论，MgO,Al2O3,TiO2,Y2O3等具有较高单位体积离解能的氧化物有利于提高玻璃的弹性模量，但玻璃弹性模量的理论计算值低于测试值，这是因为Makishima-Mackenzie理论没有考虑玻璃内阳离子的具体配位，对MgO,Y2O3堆积密度因子的堆导存在误差，因此利用Makishima-Mackenzie理论发展高弹性模量玻璃时应对MgO,Y2O3等氧化物的计算进行修正。