Ba0.65Sr0.35TiO3陶瓷材料的制备及介电特性研究

采用溶胶-凝胶工艺制备了Ba_0.65Sr_0.35TiO₃粉体,并利用微波烧结技术对粉体进行了合成和烧结,研究分析了样品的介电特性,并与传统制备工艺获得的样品进行了性能比较.实验结果表明,获得的Ba_0.65Sr_0.35TiO₃粉体颗粒较细,其合成温度和烧结成瓷温度都较传统工艺有大幅度降低,分别为900和1310℃;可以获得晶粒尺寸在1μm以内的陶瓷;随晶粒的减小,材料的相对介电常数变化不大,而介电损耗大大降低.     

纳米(Ba,Sr)TiO_3粉体材料的制备

采用溶胶 -凝胶工艺制备了 (Ba ,Sr)TiO3凝胶 ,并利用微波烧结技术对凝胶进行合成和烧结。结果表明 ,获得的 (Ba ,Sr)TiO3粉体颗粒较细 ,与传统固相反应合成法相比 ,其钙钛矿相的合成温度由 110 0℃降至 90 0℃ ;粉体的颗粒尺寸在 5 0nm附近     

磷灰石（AP）的制备及其成分比较晶体化学与吸F^—行为的研究

以热释电材料制备的非制冷焦平面已被证明具有与制冷型焦平面相竞争的优良性能，从而引起越来越多研究者的兴趣，实验研究了焦平面用（Ba,Sr)TiO3热释电陶瓷及BST／PVDF复合材料的特性，分析了晶粒尺寸对陶瓷材料热释电特性的影响，探讨了利用复合工艺制备焦平面用热释电薄膜的可能性。主要结论如下：（1）实验中首次采用微波处理的方法，对BST凝胶进行晶化处理制备陶瓷粉体，并对凝胶的热演化过程进行了分析和研究，获得了颗粒尺寸约50nm的（Ba,Sr)TiO3陶瓷粉体。分析表明，微波晶化过程也产生了中间相（Ba,Sr)CO3和TiO2，与传统晶化过程基本一致。该工艺可以在较短的时间内使凝胶完全转化为钙钛矿相，合成温度由1100℃降至900℃，所得到的粉体颗粒尺寸分布均匀，比传统固相合成法的小一个数量级。（2）首次采用居里温度较低的（Ba,Sr)TiO3纳米粉体，制备了不同体积比的BST／PVDF0－3型复合热释电材料。实验分析表明，复合体的热释电优值因子FD比BST陶瓷的提高了约30％。复保膜的厚度以及陶瓷颗粒的尺寸都对复合体的介电和热释电特性有影响，以这种方法制备的热释电材料有可能在红外焦平面的领域有广泛的应用前景。（3）微波烧结方法有效地抑制了晶粒长大，可以获得晶粒尺寸在1μm以内的（Ba,Sr)TiO3致密陶瓷。实验中，在1300℃烧结15min就已经达到95％以上的相对理论密度，晶粒尺寸约为0.32μm.研究发现，晶粒尺寸为0.8μm左右时，Ba0.80Sr0.20TiO3陶瓷的四方率（c/a）存在一个极大值。（4）实验研究了不同晶粒尺寸条件下（Ba,Sr)TiO3陶瓷的介电特性。研究表明，晶粒尺寸为0.8μm左右时，室温下材料的介电常数存在一个峰值，且弥散指数具有极小值；粒径越小，介电温谱随频率变化的程度就越小，且对电场的稳定性越好。实验首次发现，微波烧结获得的细晶粒陶瓷的介电损耗远小于传统工艺制备的样品，这一特性对于制备低噪声、高探测率的热释电材料具有重要的应用价值。（5）首次研究了（Ba,Sr)TiO3陶瓷热释电特性的晶粒尺寸效应。表明在无外置电场情况下，材料的热释电系数峰值随着晶粒尺寸的减小，在0.8μm左右有一个极大值，而后随晶粒尺寸进一步减小而迅速减小。在外场作用下，热释电峰宽化并有所下降，峰位向高温处移动。晶粒尺寸小的样品在偏场作用下热释电系数变化较小。晶粒尺寸为0.8μm的Ba0.65Sr0.35TiO3陶瓷样品具有最高的优值因子FD,且对电场有较好的稳定性，是热释电焦平面用的理想材料。     

溅射工艺对BST薄膜取向行为的影响

采用射频磁控溅射法在Si(100)衬底上沉积了Ba0.65Sr0.35TiO3薄膜.借助XRD、AFM和SEM研究了衬底温度、退火温度、溅射气压等不同的溅射参数对Ba0.65Sr0.35TiO3薄膜的晶化行为和显微结构的影响.在室温下沉积并未经退火处理的Ba0.65Sr0.35TiO3 薄膜是无定形态,在较高温度下沉积的薄膜晶化相对较好;随着在氧气气氛中退火温度的升高,X射线衍射峰的半峰宽变窄,衍射峰强度增强;在0.37～1.2Pa气压下沉积的Ba0.65Sr0.35TiO3薄膜有(110)和(200)主衍射峰,且其强度随溅射气压的增加而增强;当溅射气压继续升到3.9Pa,(110)和(200)衍射峰明显增强,说明Ba0.65Sr0.35TiO3 薄膜具有(110) (200)择优取向.AFM和SEM结果显示薄膜晶粒细小均匀、结构致密、表面平整,且无裂纹、无孔洞.分析结果显示优化工艺参数制备的Ba0.65Sr0.35TiO3 薄膜是用以制备非致冷红外探测器的优质材料.     

新型的Sol-gel法制备Ba0.6Sr0.4TiO3铁电陶瓷

采用新型的Sol-gel工艺制备了Ba0.6Sr0.4TiO3(BST)超细粉体,将BST粉体进行压制和烧结,获得了晶粒尺寸在1μm以内的BST陶瓷块体.观察了BST陶瓷块体的结晶情况并测定了其电学性能.在Sol-gel工艺中,加入了有机大分子量聚乙烯吡咯烷酮(polyvinyl pyrrolidone,PVP)制备BST前驱体.实验结果表明PVP的加入可有效增加前驱体的稳定性和分散性,降低BST陶瓷的预烧温度约250℃,并在1200℃获得晶粒细小、致密的BST陶瓷.BST陶瓷,显示弥散相变特征.     

以偏钛酸为钛源制备Sr0.05Ba0.95TiO3电子粉体

Sr0.05Ba095TiO3是一种低居里的PTC材料,探索一种以偏钛酸为钛元素来源,与碳酸钡和碳酸锶直接反应制备Sr0.05Ba0.95TiO3粉体的新方法并对制备的样品进行性能表征.本工艺所制备Sr0.05Ba0.95TiO3的平均粒度为0.35μm、粒度分布均匀、形貌为球形、(SrO BaO)/TiO2摩尔比为1.0001、Sr/Ti摩尔比和Ba/Ti摩尔比分别为0.0497和0.9504、属四方相的晶体结构、Sr0.05Ba0.95TiO3主含量为99.86%.通过此工艺的比列调整也能够制备一系列其他的SrxBa1-xTiO3粉体.     

钛酸锶钡(BaxSr1-xTiO3)陶瓷制备及其介电性能的研究

采用乙酸钡、乙酸锶和钛酸丁酯为原料的溶胶凝胶方法制备了BaxSn1-xTiO3(x=0．6)超细粉体,将BST超细粉体压制成型,进行烧结,得到(Ba0.6Sr004)TiO3陶瓷。通过热分析(DSC／TG)、X射线衍射(XRD)分析(Ba0.6Sr0.4)TiO3粉体合成过程及其相结构变化。采用扫描电子显微镜(SEM)描述(Ba0.6Sr0.4)TiO3烧结体的相结构和显微组织结构变化。阻抗分析仪测量(Ba0.6Sr0.4)TiO3陶瓷的-50～100℃介电温谱。实验结果表明BaxSn1-xTiO3粉体的相结构为立方相钙钛矿结构,其合成温度及烧结温度分别为800℃及1250℃,均低于传统工艺的相应温度。(Ba0.6Sr0.4)TiO3陶瓷在-50～100℃温度范围内,其电容率随着烧结温度升高而增大.介电损耗tgδ在-50～100℃温度范围内,随温度的增加而降低。1250℃的(Ba0.6Sr0.4)TiO3陶瓷烧结体样品存在介电峰弥散化。     

BST/PVDF复合薄膜的制备及其介电性能

以溶胶-凝胶法制备出钛酸锶钡(Ba0.65Sr0.35TiO3)粉体,并对粉体进行表面改性处理,然后将处理和未处理的粉体按不同的比例与聚偏氟乙烯(PVDF)进行复合,用甩胶法做成薄膜样品,对样品进行了介电性能的测试.实验结果表明:复合薄膜的介电常数实测值与理论值符合得较好,随着薄膜中BST粉体比例的增加,复合薄膜的介电常数和介电损耗增大;经表面改性后的BST粉体所制备的复合薄膜与未经改性所制备的薄膜相比,介电常数略有上升,而介电损耗显著下降.     

新型的Sol-gel法制备Ba0．6Sr0．4TiO3铁电陶瓷

采用新型的Sol-gel工艺制备了Ba0．6Sr0．4TiO3（BST）超细粉体，将BST粉体进行压制和烧结，获得了晶粒尺寸在1μm以内的BST陶瓷块体。观察了BST陶瓷块体的结晶情况并测定了其电学性能。在Sol—gel工艺中，加入了有机大分子量聚乙烯吡咯烷酮（polyvinyl pyrrolidone，PVP）制备BST前驱体。实验结果表明：PVP的加入可有效增加前驱体的稳定性和分散性，降低BST陶瓷的预烧温度约250℃，并在1200℃获得晶粒细小、致密的BST陶瓷。BST陶瓷，显示弥散相变特征。     

新型的Sol-gel法制备Ba0.6Sr0.4TiO3铁电陶瓷

采用新型的Sol-gel工艺制备了Ba0.6Sr0.4TiO3(BST)超细粉体,将BST粉体进行压制和烧结,获得了晶粒尺寸在1μm以内的BST陶瓷块体.观察了BST陶瓷块体的结晶情况并测定了其电学性能.在Sol-gel工艺中,加入了有机大分子量聚乙烯吡咯烷酮(polyvinyl pyrrolidone,PVP)制备BST前驱体.实验结果表明:PVP的加入可有效增加前驱体的稳定性和分散性,降低BST陶瓷的预烧温度约250℃,并在1200℃获得晶粒细小、致密的BST陶瓷.BST陶瓷,显示弥散相变特征.     

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.     

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.     

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.     

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.     

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.     

PbSbBiS4-Sb2S3 and PbSbBiS4-Bi2S3 joins in the PbS-Sb2S3-Bi2S3 system

Phase equilibria along the PbSbBiS₄-Sb₂S₃ and PbSbBiS₄-Bi₂S₃ joins of the PbS-Sb₂S₃-Bi₂S₃ system have been studied for the first time using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements, and the phase diagrams of the joins have been mapped out. The joins are shown to be pseudobinary with limited series of terminal solid solutions. The solid solutions are p-type semiconductors.     

静电纺丝法制备的Co0.6Ni0.3Cu0.1Fe2O4和Co0.6Ni0.3Zn0.1Fe2O4纳米纤维的结构及磁性能

采用静电纺丝技术制备出表面光滑、直径均匀的Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4/PVP和Co_(0.6)Ni_(0.3)Zn_(0.1)Fe_2O_4/PVP纳米纤维前驱丝,经500~900℃煅烧后得到Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4和Co_(0.6)Ni_(0.3)Zn_(0.1)Fe_2O_4纳米纤维。用TG-DSC、XRD、SEM及VSM现代测试分析手段对Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4和Co_(0.6)Ni_(0.3)Zn_(0.1)Fe_2O_4纳米纤维的结构、形貌及磁学性能进行测试表征。结果表明:在空气气氛中经500~900℃煅烧后可得到纯尖晶石相、结晶度良好的纳米纤维或短纤维;当温度为700℃时,Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4和Co_(0.6)Ni_(0.3)Zn_(0.1)Fe_2O_4纳米纤维的形貌细长而光滑且直径相对均匀,大约为80nm;此时Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4纳米纤维则保有较高的剩磁比(M_r/M_s)及矫顽力,分别为0.56和1 088.87Oe。在500℃、600℃、700℃、800℃、900℃煅烧后,Co_(0.6)Ni_(0.3)Zn_(0.1)Fe_2O_4纳米纤维的饱和磁化强度分别比Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4纳米纤维增大了14.5%、7%、16%、10.7%、8%,而矫顽力则分别降低了38%、51%、50%、46%、46.7%。两种纳米纤维的饱和磁化强度及矫顽力存在差异,为CoNi铁氧体在电磁方面的应用提供了很好的参考。     

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.     

Vapour-liquid equilibria in the ternary mixtures N2---CH4---C2H6 and N2---C2H6---C3H8

A systematic study was performed with mixtures consisting of N₂, CH₄, C₂H₆ and C₃H₈, to investigate experimentally phase equilibria and caloric properties and to test the accuracy of thermodynamic correlations. The first part of this Paper reports results of T---p---x---y measurements on ternary systems in the range 20 < p < 120 bar and 140 < T < 220 K. The results are compared with data calculated by generalized equations of state.     

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.