Ba2Fe1+xMo1-xO6双钙钛矿的制备与磁卡效应

采用湿化学法制备了一系列Ba2Fe1+xMo1-xO6双钙钛矿材料,研究了Fe/Mo原子比对其磁性能尤其是磁卡效应的影响.实验结果表明,随着x增加,样品的磁化强度由x=0时的37.3A·m2/kg(3.49μB/f.u.)下降到x=0.3时30.4A·m2/kg(2.78μB/f.u.);当x=0时,样品的最大磁熵变值为1.54J/kg·K.随着x增加,样品的最大磁熵变值逐渐下降,磁熵变随温度变化曲线的峰形变宽.     

钴掺杂Sr4Fe6O13混合导体氧化物结构及透氧测定

用湿化学法合成了Sr     

氧化锑/高岭土复合阻燃微粉的湿化学反应动力学及特性

采用湿化学法制备了氧化锑/高岭土复合阻燃微粉,用热重（TG）,差示扫描量热法（DSC）对其阻燃特性进行了分析,用SEM分析了粒子形貌,激光光散射粒度分布仪分析了粒子的分布情况.热分析结果表明,与球磨法相比,湿化学法制备的样品的失重量大,失重温度范围广,放热峰范围广. 化学法制备复合微粉的反应活化能与球磨法相差不大. SEM分析及粒度分析表明:复合微粉大多处于0.20 μm以下, 化学法制备的样品中以锑白粉占为主,高岭土附在锑白粉表面,充分与锑白粉发生物理、化学作用.同时发现,样品经600 ℃热处理2 h后,粒子结合更加紧密.     

化学还原法制备Fe3O4纳米颗粒及其性能研究

采用化学还原法制备得到了Fe3O4纳米颗粒,并用XRD对制备条件:分散剂种类、分散剂用量、煅烧温度、煅烧时间进行了研究。研究结果表明,当选用PEG(6000)做分散剂,PEG用量为50g/L,煅烧温度为700℃,煅烧时间为120min时,制备得到的Fe3O4纳米颗粒已经具有晶型完整的反尖晶石结构。将该样品做VSM分析,分析结果表明样品饱和磁化强度可达85A.m2/kg,并且矫顽力趋近于0,呈现出良好的顺磁性。     

氧化锑/高岭土复合阻燃微粉的湿化学法制备及特性

采用湿化学法制备了氧化锑 /高岭土复合阻燃微粉 ,用热重 (TG)、差示扫描量热法 (DSC)对其阻燃特性进行了分析 ,用SEM分析了粒子形貌 ,激光光散射粒度分布仪分析了粒子的分布情况。热分析结果表明 ,与球磨法相比 ,湿化学法制备的样品的失重量大、失重温度范围广、放热峰范围广 ;化学法制备复合微粉的反应活化能与球磨法相差不大。SEM分析及粒度分析表明 :复合微粉大多处于 0 .2 0 μm以下 ,化学法制备的样品中以锑白粉为主 ,高岭土附在锑白粉表面 ,充分与锑白粉发生物理、化学作用。同时发现 ,样品6 0 0℃热处理 2h后 ,粒子结合更加紧密     

由SiO2/3Y-TZP包裹复合粉体制备ZrSiO4/3Y-TZP细晶陶瓷

对湿化学法制备的SiO2/3Y-TZP包裹复合粉体进行了热压烧结研究，并利用X射线衍射和透射电镜表征了烧结体的物相和显微结构。在低于1300℃，复合粉体发生瞬时粘性烧结，材料密度迅速提高，随着烧结温度的升高，SiO2和ZrO2发生反应生成ZrSiO4。在1500℃热压条件,制备了平均晶粒尺寸为350nm的ZrSiO4/3Y-TZP细晶复相材料。我们认为，在烧结过程中形成的第二相ZrSiO4，特别SiO2包裹层对抑制基体晶粒工大起主要作用。     

湿化学法制备纳米WO3粉体的研究进展

综述了目前国内外湿化学法制备纳米WO3粉体的主要方法:水解法、沉淀法、溶胶-凝胶法、水热合成法及微乳液法,并对各种制备方法的优缺点进行了简要的讨论.与传统方法相比,湿化学法制备的纳米WO3粉体更细且粒径分布可控、均匀性及分散性好.     

放电等离子烧结技术制备Fe78Si13B9块体非晶纳米晶磁性材料

通过高能球磨技术制备了Fe₇₈Si₁₃B₉磁性非晶合金粉体,采用XRD和DSC分析了Fe₇₈Si₁₃B₉非晶合金粉体的相组成、玻璃转变温度T_g、开始晶化温度 T_x 和晶化峰温度T_p;利用放电等离子烧结（SPS）技术在不同烧结温度下制备了块体磁性非晶纳米晶合金试样,利用XRD、SEM、Gleeble3500、VSM等分析了不同烧结温度下烧结块体试样的相转变特性、微观形貌、力学性能和磁学性能。结果表明,在500 MPa的烧结压力下,随着烧结温度的升高,烧结试样中的非晶相开始逐渐晶化,烧结试样的致密度、抗压强度、微观硬度、饱和磁化强度均显著提高;在500 MPa的烧结压力和823.15 K的烧结温度下,获得了密度为6.6 g/cm³,抗压强度为1500 MPa,饱和磁化强度为1.3864 T的非晶纳米晶磁性材料。     

α-Al2O3籽晶对Al2O3晶型转变及形貌的影响

在湿化学法合成的纳米Al2O3前驱体NH4Al(0H)2CO3中添加α-Al2O3籽晶(150nm左右)，研究了α-Al2O3籽晶对Al2O3晶型转变及形貌的影响．结果表明，少量Q—A1203籽晶的添加能降低形核温度，有效的提高相转变速率，在较低的温度下完成θ→α-Al2O3的相转变，同时对聚合生长也产生一定的影响．     

纳米γ-Fe2O3粒子的制备及其性能研究

以乙二醇作为前驱体,采用溶胶——凝胶法制备出了纳米γ-Fe2O3粒子,讨论了灼烧温度等对粒子大小、形貌、磁性等的影响,并采用红外光谱、X射线衍射光谱、透射电子显微镜、比表面分析仪及振动样品磁强计等对粒子的性能进行表征.结果表明:当烧结温度为450℃时,实验所得到的粒子的粒径最小,为5nm左右,磁性最强,比饱和磁化强度为65 emu.g-1,且分散较均匀.     

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。