单相Bi0.9Ba0.1Fe0.85Mn0.15O3陶瓷中的多铁性

溶胶-凝胶法制备了Bi0.9Ba0.1Fe0.85Mn0.15O3陶瓷样品,XRD分析显示其为单相菱方钙钛矿结构,明显的磁滞回线和电滞回线说明其在室温具有弱铁磁性和铁电性,介电常数随外磁场的变化显示双掺样品具有更大的磁容效应.     

(La1-xPrx)2/3Sr1/3MnO3系列的磁致伸缩效应研究

用溶胶-凝胶方法制备了一系列的(La_1-xPr_x)_2/3Sr_{1/3MnO3多晶样品,研究了其电磁性能及磁致伸缩效应,发现样品低温下的磁致伸缩主要以线伸缩为主,且在低场下达到饱和,在Pr含量为0.3时达到最大值,约为-90×10^-6.随Pr掺杂含量的逐渐减小,磁致伸缩的饱和场也逐渐减小. 关键词：}     

(Ni0.8Zn0.2Fe2O4)epoxy-PZT双层膜中的磁电效应

讨论了Ni_0.8Zn_0.2Fe₂O₄ (NZFO)与锆钛酸铅(PZT)的双层膜结构样品的磁电(ME)效应.NZFO粉料由溶胶-凝胶法制成，再经900℃热压，并高温烧结.在该双层膜中测量到了很强的磁电相互作用.发现横向的磁电效应比纵向效应大一个数量级，并且随NZFO烧结温度的提高而增加.当烧结温度从950℃上升到1380℃时，横向ME电压系数(α_E)的最大值变化范围为25.6 mV Am^-2≤α_E≤199.6 mV Am^-2.理论分析显示NZFO-PZT双层膜样品中ME效应源于NZFO与PZT之间相对良好的磁电耦合. 关键词： 镍铁氧体 PZT 热压法 ME效应     

La0.8-xCa0.2MnO3纳米颗粒的居里温度与磁热效应

采用溶胶凝胶法制备了系列La_0.8-xCa_0.2MnO₃多晶样品,用X射线衍射分析确定了样品的钙钛矿结构,用透射电子显微镜观察了样品的形貌及粒径分布情况,用PAR155型振动样品磁强计测量了样品的磁性随外场和温度的变化,确定样品的居里温度并计算了各样品的磁熵变.磁测量及计算结果表明制备的各样品的居里温度在180—260K的范围内且随焙烧温度和La³⁺离子空位浓度的不同而变化,不同温度焙烧的样品均有较大的磁熵变值,其中1100℃焙烧的La_0.77Ca_0.2MnO₃,多晶样品在240.5K,H=1.0T的外场下的磁熵变达3.76J/kg·K,对实验结果做了定性的分析.该材料具有较高的居里温度和较大的磁熵变,所需外场强度适中,电阻率高,性能稳定,适合做高温磁制冷材料. 关键词： 钙钛矿 居里温度 磁热效应     

CoFe2O4和MnFe2O4纳米复合介质的制备及其磁性研究

采用热分解法制备了分散程度高且平均晶粒尺寸为20 nm的CoFe₂O₄和MnFe₂O₄复合介质.低温磁化曲线测量显示,制备的复合介质具有软-硬磁交换弹性耦合效应,且合成温度以及软磁和硬磁相的成分比例对磁交换弹性耦合的强度有很大的影响.变温磁测量显示,温度为20K时,复合纳米介质的表面自旋冻结效应导致饱和磁化强度显著增加.Henkel测量显示,对分散的CoFe₂O₄和MnFe₂O₄复合介质,磁偶极相互作用占主导作用.     

SrTiO3掺杂La-K-Mn-O系统的电磁性质

用溶胶-凝胶制备了La_0.833K_0.167MnO₃-SrTiO₃ (LKMO/STO)系列样品，并研究了它们的结构、磁性和输运特性.X射线衍射实验表明，1200℃烧结的LKMO/STO (STLK12)是一个均匀的固溶相.其电阻率表现为绝缘体的行为，而纯La_0.833K_0.167MnO₃ (LKMO)样品随温度的升高则有金属-绝缘体转变.在低场下(μ₀H=0.02 T)，对STLK12样品，当温度从220 K降低到4 K时，磁电阻从0.2%升高到11%.在高场下(μ₀H=5.5 T)，随着温度降低，磁电阻几乎是线性增大.在4.2 K时，达到65%.比纯LKMO样品40%的磁电阻高出了25%. 我们用晶界处的自旋极化隧穿效应定性地解释了这种增强的磁电阻效应. 关键词： 低场磁电阻 高场磁电阻 自旋极化隧穿 钙钛矿     

晶粒尺寸对Bi0.2Ca0.8MnO3电荷有序的影响

利用溶胶-凝胶法制备了平均晶粒尺寸在38—1500 nm的系列Bi_0.2Ca_0.8MnO₃多晶样品,研究了它们的结构、电输运性质和磁性.研究结果表明,随着晶粒尺寸的减小,电荷有序逐渐消失、最后被完全压制,导致低温下出现自旋玻璃态.利用马氏体相变图像和表面效应解释了相关现象. 关键词： 钙钛矿锰氧化物 电荷有序 马氏体相变 自旋玻璃     

钙钛矿锰氧化物La0.7Sr0.3MxMn1-xO3(M=Cr,Fe)的巨磁电阻效应与磁性

研究了溶胶-凝胶法制备氧化物巨磁电阻材料的工艺,制备了La_0.7Sr_{0.3< /sub>CrxMn1-xO3(x=0,0.10,0.15)和La0.7Sr0.3FexMn1-xO3(x=0.05,0.10,0.16)两 系列的单相钙钛矿锰氧化物多晶样品,并研究了Cr,Fe替代La0.7Sr0.3MnO3中部分Mn后对其结构、磁性和巨磁电阻性质的影响.观察到La0.7 Sr0.3Cr0.15Mn0.85O3和La0. 7Sr0.3Fe0.05Mn0.95O3两个样品的 电阻-温度曲线都出现了双峰.定性讨论了可能产生双峰的机制.随Cr(或Fe)替代量的增加, 材料的居里温度很快下降,铁磁性减弱,导电性降低,巨磁电阻效应增强.但与Fe掺杂相比 ,相同数量的Cr掺杂对材料的影响要小. 关键词： 巨磁电阻效应 溶胶-凝胶工艺 电阻-温度曲线 金属绝缘体转变}     

前驱溶液的pH值对制备Ca2Zn4Ti16O38 ∶ Pr3+,Na+ 发光粉物相、形貌和发光性质的影响

以钛酸丁酯、醋酸钙、醋酸锌、柠檬酸和乙二醇为原料,采用溶胶-凝胶法制备Ca₂Zn₄Ti₁₆O₃₈ ∶ Pr³⁺, Na⁺ 发光粉。研究了前驱溶液的pH值对溶胶-凝胶转变过程、发光粉物相组成、样品形貌和发光性质的影响。通过热重-差热分析(TG/DTA)、X射线衍射(XRD)分析、扫描电子显微镜(SEM)对前驱物分解、发光粉物相和颗粒大小进行了研究。采用荧光光谱对材料的光谱性质进行了表征。研究发现前驱溶液pH ≤ 3时,所得发光粉样品为蓬松的、颗粒均匀的单相Ca₂Zn₄Ti₁₆O₃₈粉末,红色余辉时间较长;随着pH值增大,逐渐有杂质相TiO₂、CaTiO₃和Zn₂TiO₄生成,并且样品颗粒逐渐变大,颗粒团聚呈现不规则形状,余辉时间变短。结果表明,只有在pH ≤ 3条件下以溶胶-凝胶法制备Ca₂Zn₄Ti₁₆O₃₈ ∶ Pr³⁺, Na⁺ 发光粉下才能获得被日光有效激发,并呈现余辉衰减慢的红色长余辉(644 nm)发光。     

Ag/Bi4Ti3O12栅n沟道铁电场效应晶体管制备及存储特性

在溶胶-凝胶工艺获得高质量Bi₄Ti₃O₁₂薄膜的基础上 ，制备了Ag/Bi₄Ti₃O₁₂栅n沟道铁电场效应晶体管. 研 究了Si基Bi₄Ti₃O₁₂薄膜的生长特性及其对铁电薄膜/ 硅的界面状态和铁电场效应晶体管存储特性的影响. 研究表明，在合理的工艺条件下可以获 得具有较高c-轴择优取向的纯钙钛矿相Si基Bi₄Ti₃O₁₂ 铁电薄膜并有利于改善Bi₄Ti₃O₁₂/Si之间的界面特性; 顺时针回滞的C-V特性曲线和C-T曲线表明Ag/Bi₄Ti₃O_{12栅n沟道铁电场效应晶体管具有极化存储效应和一定的极化电荷保持能力; 器件的转移(I< sub>sd}-V_G)特性曲线显示Ag/Bi₄Ti₃O_{12栅n沟道铁电场效应晶体管具有明显的栅极化调制效应. 关键词： 铁电场效应晶体管 4}Ti₃O₁₂')" href="#">Bi₄Ti₃O₁₂ 存储 特性 溶胶-凝胶工艺     

La0.3Sr0.7TiO3模板层对Pb(Zr0.5Ti0.5)O3薄膜的铁电性能增强效应的研究

通过sol-gel法在Si (111) 基片上分别制备了LaNiO₃(LNO)底电极和LaNiO₃/La_0.3Sr_0.7TiO₃ (LNO/LSTO)底电极.然后采用sol-gel 方法，在两种衬底上分别制备了Pb (Zr_0.5Ti_0.5)O₃ (PZT)铁电薄膜.XRD分析表明，两种PZT薄膜均具有钙钛矿结构，且在LNO底电极上的PZT薄膜呈(100) 择优取向，而在LNO/LSTO底电极上的PZT薄膜呈随机取向.铁电性能测试表明，相对LNO衬底上制备的PZT薄膜，在LNO/LSTO底电极上制备的PZT薄膜的剩余极化强度得到了有效的增强，同时矫顽场也增大.介电常数和漏电流的测试表明，LNO/LSTO底电极上制备的PZT薄膜具有大的介电常数和漏电流. 关键词： PZT薄膜 铁电性 漏电流 0.3Sr_0.7TiO₃')" href="#">La_0.3Sr_0.7TiO₃     

Solvothermal one-step synthesis of MWCNTs/Ni0.5Zn0.5Fe2O4 magnetic composites

A magnetic multi-walled carbon nanotubes-based (MWCNTs-based) composite, MWCNTs/Ni_0.5Zn_0.5Fe₂O₄, was synthesized via a facile solvothermal approach. The composites were characterized by X-ray diffraction analysis, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and vibrating sample magnetometry. The results confirmed that MWCNTs and Ni_0.5Zn_0.5Fe₂O₄ coexisted in the composites. The TEM and HRTEM results showed a thick layer of Ni_0.5Zn_0.5Fe₂O₄ was intimately connected to the surface of MWCNTs. The saturation magnetization value of the composites was 45.8 emu/g. Furthermore, the probable synthesis mechanism of the magnetic composites was also investigated based on the experimental results.     

Optical properties of surface-modified Bi2O3 nanoparticles

Stearic acid coated Bi₂O₃ nanoparticles in the size range of 5-13 nm were synthesized by the microemulsion method. HRTEM showed that the morphology of Bi₂O₃ nanoparticles was ellipsoidal. The absorption edge of Bi₂O₃ nanoparticles showed a blue shift of ∼0.45 eV, comparing with that of the bulk Bi₂O₃. At room temperature, Bi₂O₃ nanoparticles also showed a strong luminescence at 397 and 420 nm, depending on the excitation wavelength.     

Preparation and characterization of co-doped (Ce0.80La0.15Al0.05O1.90) and multiple-doped (Ce0.80Sm0.10Gd0.05Al0.05O1.90 and Ce0.80Gd0.10Sm0.05Al0.05O1.90) ceria

Attempts have been made to synthesize a few compositions Ce_0.80La_0.15Al_0.05O_1.90, Ce_0.80Sm_0.10Gd_0.05Al_0.05O_1.90, and Ce_0.80Gd_0.10Sm_0.05Al_0.05O_1.90 by citrate–nitrate auto-combustion method. The aim of the present investigation was to study the effect of co-doping and multiple doping on the ionic conductivity of CeO₂ for its use as solid electrolyte in intermediate temperature solid oxide fuel cells. XRD patterns showed that all the samples have fluorite-type crystal structure similar to undoped ceria. Microstructures of thermally etched samples have been studied by scanning electron microscopy. Contributions of grains σ _g and grain boundaries σ _gb to the total conductivity σ _T, have been determined using impedance analysis. Impedance measurements were made in the frequency range 1 Hz–1 MHz and temperature range 250–500 °C. Our experimental results show that multiple doping is more effective than co-doping for improving the oxide ion conductivity of ceria in the materials investigated in the present study.     

Electrical properties of neodymium doped CaBi4Ti4O15 ceramics

Neodymium doped bismuth layer structure ferroelectrics (BLSFs) ceramics CaBi_4−xNd_xTi₄O₁₅ (x=0, 0.25, 0.50, 0.75) were prepared by solid-state reaction method. X-ray diffraction pattern showed that single phase was formed when x=0-0.75. The refined lattice parameters showed that a (b) axes decrease at x=0.25 and increase with more Nd³⁺ dopant. The effects of Nd³⁺ doping on the dielectric and ferroelectric properties of CaBi₄Ti₄O₁₅ ceramics are studied. Nd³⁺ dopant decreased the Curie temperature linearly, and the dielectric loss, tan δ, as well. The remnant polarization of Nd³⁺ doped CaBi₄Ti₄O₁₅ ceramics was increased by 80% at x=0.25, while more Nd³⁺ dopant decreased the remnant polarization. CaBi_3.75Nd_0.25Ti₄O₁₅ ceramics had the largest piezoelectric constant d₃₃. The structure and properties of CaBi_4−xNd_xTi₄O₁₅ ceramics showed that Nd³⁺ may occupy different crystal locations when Nd³⁺ content x is less than 0.25 and more than 0.50.     

Fabrication and characterization of epitaxial Sr0.6Ba0.4Nb2O6/La0.7Sr0.3CoO3 heterostructures

Epitaxial Sr_0.6Ba_0.4Nb₂O₆(SBN60)/La_0.7Sr_0.3CoO₃ heterostructures were fabricated on LAO(0 0 1) substrates using pulsed laser deposition (PLD). Their structural properties were investigated by X-ray diffraction. The θ-2θ scans showed single crystalline Sr_1−xBa_xNb₂O₆ (SBN) and La_xSr_1−xCoO₃ (LSCO) layers with a 〈0 0 1〉 orientations perpendicular to the substrate plane. Phi scans on the (2 2 1) plane of SBN layer indicated that the films have two in-plane orientations with respect to the substrate. The SBN unit cells were rotated in the plane of the film by ±18.4° as well as ±45° with respect to the LAO substrate. This rotation was explained by considering the lattice matching between films and substrate, and minimization of electrostatic energy. Spectroellipsometry (SE) was used to characterize the depth profile, the microstructural inhomogeneities, including voids and surface roughness, refractive indices and extinction coefficients of the films.     

High temperature transport properties of Ag-added (Ca0.975La0.025)3Co4O9 ceramics

Ag-added (Ca_0.975La_0.025)₃Co₄O₉ ceramics were fabricated using spark plasma sintering from the precursor powder synthesized by a polyacrylamide gel method. The results indicated that Ag precipitated as a second phase in Ca₃Co₄O₉ matrix. The addition of Ag was effective in enhancing the electrical conductivity and had a slight effect on Seebeck coefficient. In addition, the temperature dependence of electrical conductivity showed that the hole hopping conduction mechanism was dominant for the Ag-added (Ca_0.975La_0.025)₃Co₄O₉ ceramics. The activation energy remained unchanged with the increasing Ag content. The thermoelectric power factor of Ag-added (Ca_0.975La_0.025)₃Co₄O₉ ceramics reached about 5×10⁻⁴ Wm⁻¹ K⁻² at 700 °C, suggesting a promising thermoelectric oxide candidate at high temperatures.     

深过冷Cu60Sn30Pb10偏晶合金的快速凝固

实现了大体积Cu₆₀Sn₃₀Pb₁₀偏晶合金的深过冷与快速凝固. 实验获得的最大过冷度为173 K(0.17T_L). 凝固组织发生了明显的宏观偏析,XRD分析表明,试样上部是由固溶体(Sn),(Pb)相和金属间化合物ε(Cu₃Sn)相组成的三相区,下部为富(Pb)相区. 在小过冷条件下,三相区中ε(Cu₃Sn)相的凝固组织为粗大的枝晶,随着过冷度的增大,ε(Cu₃Sn)相细化成层片状组织,且层片间距随过冷度的增大而减小,而(Sn),(Pb)两相始终以离异共晶的方式存在. 富(Pb)相区中分布有少量的ε(Cu₃Sn)枝晶,枝晶长度随过冷度的增大而增大,且在大过冷条件下发生碎断. (Sn)相在ε(Cu₃Sn)相表面形核、长大,其形态类似于包晶凝固组织. 关键词： 深过冷 快速凝固 偏晶合金 层片组织     

Ultrafast nonlinear optical properties of Bi2O3-B2O3-SiO2 oxide glass

The ultrafast nonlinear optical properties of Bi₂O₃-B₂O₃-SiO₂ oxide glass were investigated using a femtosecond optical Kerr shutter (OKS) at wavelength of 800 nm. The nonlinear response time of this Bi₂O₃-doped glass was measured to be <90 fs. The nonlinear refractive-index n₂ was estimated to be 1.6 × 10⁻¹⁴ cm²/W. Measurements for the dependence of Kerr signals on the polarization angle between the pump and probe beams showed that the Kerr signals induced by 30-fs pulse laser arose mainly from the photoinduced birefringence effect.     

Synthesis and characterization of MnFe2O4-BiFeO3 multiferroic composites

The mixed spinel-perovskite composites of xMnFe₂O₄-(1-x)BiFeO₃ with x=0, 0.1, 0.2, 0.3 and 0.4 were prepared by solid state reaction method. The structure and grain size were examined by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. The XRD results showed that the composites consisted of spinel MnFe₂O₄ and perovskite BiFeO₃ phases after being calcined at the temperature 950 °C for 2 h. The grain size ranged from 0.8 to 1 μm. Magnetization was found to increase with increasing concentration of ferrite content. The variation of dielectric constant and dielectric loss with frequency showed dispersion in the low frequency range. Magnetocapacitance was also observed in the prepared composites, which may be the sign of magnetoelectric coupling in the synthesized composites at room temperature.