共沉淀法制备钒掺杂钛酸铋粉体及其陶瓷性能研究

采用共沉淀法制备了掺钒钛酸铋粉体，研究了粉体的晶化过程、微观形貌和烧结性能．与传统固相反应法相比，共沉淀法合成钛酸铋相的反应可在550℃完成，比固相反应法低250℃左右，所得粉体的粒径〈100nm．此外，共沉淀法制备的粉体具有良好的烧结性能，在900℃达到理论密度的96％．与固相法烧结陶瓷相比，共沉淀粉体制备的材料具有更低的介电损耗．     

钛酸铋陶瓷及其电性能的研究

采用NaCl-KCl熔盐法合成出片状钛酸铋粉体,并制备了钛酸铋陶瓷.对所得陶瓷进行了相结构与显微组织及电性能的研究,结果表明,粉体烧结后为纯钙钛矿型钛酸铋陶瓷,微观形貌呈片状,并且随粉体合成时所用熔盐含量的增加,陶瓷晶粒的片状尺寸不断增大,其介电常数先减小,后增加,熔盐为5%(质量分数)时合成的粉体烧结成瓷后,其介电常数具有最小值,同时电阻率则随着合成粉体时所用熔盐含量的增加不断增加.     

高活性锆钛酸铅压电陶瓷粉体的合成及其烧结性能研究

以Pb3O4、ZrO2和TiO2为原料,采用冲击波加载技术合成锆钛酸铅Pb(Zr0.95Ti0.05)O3粉体,并对粉体活性和烧结特性进行XRD和SEM表征,研究结果表明,利用冲击波的高温高压作用可以合成单一钙钛矿相锆钛酸铅粉体,合成粉体产生了细化并存在一定程度的晶格畸变,有利于增强粉体活性,促进了低温活化烧结,也显著地改善了陶瓷的烧结性能,在常压下1200℃烧结150min得到了密度达到7.83g/cm3的锆钛酸铅95/5陶瓷体,比传统固相法制备的粉体烧结温度降低了100℃左右,且得到的陶瓷体晶粒形状、大小均匀。     

压电陶瓷CaxSr（1-x）Bi4Ti4O15的制备及其性能研究

通过固相合成法制备CaxSr1-xBi4Ti4O15（x=0.3，0．4，0．5）无铅压电陶瓷，通过XRD、SEM等测试方法对粉体及陶瓷进行了分析与表征，并利用HP4294网络分析仪、d33准静态测试仪等分析了相关性能随X的变化关系。分析表明，利用固相法合成钛酸铋锶钙粉体的较好温度为850℃，钛酸铋锶钙陶瓷的较好烧结温度为1210℃，密度为6．821g/cm^3，达到理论密度的91％，x=0.4时，压电常数达到22×10^-12C/N。     

工艺参数对熔盐法制备Bi4Ti3012的影响

为了获得片状粉体用于无铅压电陶瓷晶粒的定向生长，采用NaCl-KCl熔盐法制备了各向异性的片状Bi4Ti3O12粉体，研究了预烧温度和熔盐含量对粉体的显微组织结构和形貌各向异性的影响，计算了粉体径向尺寸与厚度尺寸的比值以表征粉体的各向异性．研究表明：随着预烧温度的升高，粉体尺寸不断增加，各向异性逐渐增大，最佳预烧温度为950℃；采用熔盐法可制备出纯Bi4Ti3O12相粉体，随熔盐含量增加，钛酸铋粉体尺寸及各向异性程度明显增大，并在烧结后的Bi4Ti3O12陶瓷中有织构产生．     

溶胶-凝胶法制备适用于还原性气氛下烧结的钛酸钡基超细粉体

以醋酸钡、钛酸四丁酯和冰醋酸为主要原料,采用溶胶-凝胶方法制备出适用于还原气氛下烧结的超细钛酸钡基陶瓷粉体.利用差热分析研究了前驱体的热转变过程.利用XRD分析了在不同烧结温度下,粉体的相结构.利用透射电镜研究了温度对粉体粒度和形貌的影响.实验结果表明,所得干凝胶在600℃度煅烧后就可以得到均匀且均相的掺杂改性钛酸钡粉体.在700℃度煅烧1h后,就可以得到形貌规则,粒度为100nm左右的高纯掺杂改性钛酸钡粉体.     

溶胶-凝胶法制备Na0.5Bi0.5TiO3基无铅压电陶瓷的研究进展

钛酸铋钠(Na0.5Bi0.5TiO3,简写为NBT)基无铅压电陶瓷由于具有良好的压电性、高居里温度和烧结过程中无毒、易控制性等优点而备受关注.综述了溶胶-凝胶法制备Na0.5Bi0.5TiO3粉体及制备出的陶瓷的结构和性能特点.总结了用溶胶-凝胶法制备压电和介电性能显著提高的钛酸铋钠基无铅压电陶瓷的研究进展.研究表明,溶胶-凝胶法在制备压电陶瓷方面具有均匀性好、纯度高,烧结温度低等优点.展望了该工艺的发展方向.     

非水解和水解溶胶-凝胶法合成钛酸铝粉体的研究对比

分别采用非水解和水解溶胶-凝胶法合成钛酸铝粉体,利用FT-IR、DTA-TG、XRD、SEM等方法研究了溶胶-凝胶转变和合成相变化过程及粉体烧结性能.结果发现:水解凝胶过程中Al3+以网络外离子形式富集于Ti-O-Ti凝胶网络之间,凝胶依次晶化成金红石和刚玉,再通过固相扩散在1350℃时合成钛酸铝,粉体粒径为1～2μm,比表面积仅3.2m2/g,1400℃烧结后抗弯强度为7.2MPa.非水解凝胶化过程中Al3+和Ti4+通过聚合共同形成凝胶网络,其在网络结构中地位趋同,凝胶在 750℃已直接由无定型晶化为钛酸铝,粉体粒径为0.1～0.3μm,比表面积与抗弯强度分别为水解法样品的35倍和2.3倍,性能较好.     

工艺参数对熔盐法制备Bi4Ti3O12的影响

为了获得片状粉体用于无铅压电陶瓷晶粒的定向生长,采用NaCl-KCl熔盐法制备了各向异性的片状Bi4Ti3O12粉体,研究了预烧温度和熔盐含量对粉体的显微组织结构和形貌各向异性的影响,计算了粉体径向尺寸与厚度尺寸的比值以表征粉体的各向异性.研究表明:随着预烧温度的升高,粉体尺寸不断增加,各向异性逐渐增大,最佳预烧温度为950℃;采用熔盐法可制备出纯Bi4Ti3O12相粉体,随熔盐含量增加,钛酸铋粉体尺寸及各向异性程度明显增大,并在烧结后的Bi4Ti3O12陶瓷中有织构产生.     

Pb(Zr0.95Ti0.05)O3粉体的冲击波合成及烧结研究

以ZrO2、Pb304和TiO2为原料（Nb2O5为掺杂剂），采用柱面冲击波装置合成了Pb（Zr0.95 Ti0.05）O2（PZT95／5）粉体，并对粉体活性及其烧结性能进行了研究。XRD及SEM分析表明，利用冲击波的高温高压作用可以合成单一钙钛矿相PZT95／5粉体，并使得粉体发生了晶粒细化与晶格畸变，这有利于增强粉体活性，促进低温活化烧结。该粉体在1100℃的低温下即可烧结成瓷；在1200℃烧结3h，陶瓷体致密度达到最大，约7．79g／cm^3，且晶粒尺寸相近，分布均匀。     

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.     

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.     

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.     

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.     

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.     

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.