溶胶凝胶法制备超细负热膨胀性ZrW2O8粉体

以溶胶凝胶法制备负热膨胀材料ZrW2O8粉体并与固相法制备的粉体相比较.对其前驱体进行热重-差热分析(TG-DSC)、以X射线粉末衍射(XRD)、透射电镜(TEM)、扫描电子显微镜(SEM)分别对粉体进行物相分析和形貌观测.结果表明溶胶凝胶法比固相法合成温度低,于610℃合成单一立方结构ZrW2O8粉体,并且粉体颗粒比固相法小,为100nm;ZrW2O8粉体有很好的负热膨胀特性,以高温X射线衍射分析,在室温约500℃范围内,溶胶凝胶法制备的粉体的热膨胀系数为-5.93×10-6/K;比固相法(-6.31×10-6/K)的略低.     

固相法制备超细ZrW2O8粉体及其负热膨胀特性的研究

以化学合成的ZrO2和WO3为原料,以固相法制备具有负热膨胀特性的超细立方相ZrW2O8粉体.对其前驱体进行差热分析(DSC),以X射线粉末衍射(XRD)、扫描电子显微镜(SEM)及透射电子显微镜(TEM)对产物结构及形貌进行表征.结果表明:通过化学方法合成出单斜相和四方相混合的纳米级ZrO2粉体,纯单斜相的纳米级WO3粉体,以其为原料能够制备出超细立方相ZrW2O8粉体.同时考察不同研磨时间对其粒径的影响.变温X射线粉末衍射分析表明:所得ZrW2O8粉体具有很好的负热膨胀特性,在20～600℃范围内的平均热膨胀系数为-6.82×10-6K-1.     

共沉淀法合成负热膨胀材料ZrW2O8

ZrW2O8是极具应用前景的各向同性负热膨胀材料.用共沉淀法合成了ZrW2O8,经X射线衍射、红外-拉曼光谱分析证明用共沉淀法合成的ZrW2O8纯度高.经高温X射线衍射测定,ZrW2O8在298～973K温度区间线膨胀系数αl=-7.0×10-6K-1, α-ZrW2O8(空间群P213)相到β-ZrW2O8(空间群Pa3)的转变温度在443K与446K之间.对ZrW2O8前驱体进行了热重-差热分析(TG-DTA).     

柠檬酸溶胶-凝胶法合成负热膨胀性ZrW_2O_8粉体及其性质研究

以柠檬酸为螯合剂,采用溶胶-凝胶法制备负热膨胀性Zr W2O8粉体,对其前驱体进行热重-差热分析,以X射线粉末衍射、扫描电子显微镜对产物结构及形貌进行表征,结果表明所得粉体为单一α-Zr W2O8相,具有无规则形状。随着柠檬酸量的增加,颗粒有明显聚集长大的趋势,且形貌向片层状发展。变温X射线粉末衍射分析表明,所得Zr W2O8粉体具有很好的负热膨胀特性,在室温~500℃时,平均热膨胀系数为-6.14×10-6/℃。     

脉冲激光沉积ZrW2O8薄膜的制备和性能

采用脉冲激光沉积法在石英基片上沉积制备了ZrW2O8薄膜.用X射线衍射仪(XRD)、原子力显微镜(AFM)研究了不同衬底温度对薄膜结构组分、表面粗糙度和形貌的影响,用台阶仪和分光光度计测量薄膜的厚度和不同衬底温度下制备薄膜的透射曲线,用变温XRD分析了ZrW2O8薄膜的负热膨胀特性.实验结果表明:在衬底温度为室温、550℃和650℃下脉冲激光沉积的ZrW2O8薄膜均为非晶态,非晶膜在1200℃保温3min后淬火得到立方相ZrW2O8薄膜;随着衬底温度的升高,ZrW2O8薄膜的表面粗糙度明显降低;透光率均约为80%,在20～600℃温度区间内,脉冲激光沉积制备的ZrW2O8薄膜的负热膨胀系数为-11.378×10-6 K-1.     

纳米颗粒包覆ZrW_2O_8空心结构的制备和性能

采用包覆法制备单一相钨酸锆(ZrW2O8)空心球。研究选择以水热合成法制备的胶体碳球作为制备空心球的模板,通过溶胶—凝胶法制备了具有网状结构的钨酸锆前驱体凝胶,经过后续简单的包覆过程得到胶体碳球—钨酸锆凝胶形成的壳核结构,并对该壳核结构进行煅烧(610℃保温10h)后除去碳球模板得到ZrW2O8空心球。实验所得ZrW2O8空心球平均粒径约3μm,球壳平均厚度为1.5μm,构成壳层结构的纳米级ZrW2O8颗粒为棒状无规则多面体,尺寸约500nm×50nm×50nm。FTIR和TG-DTA分析证明,产物为立方相ZrW2O8空心球,密度为2.8g/cm3,比理论值降低了45%;产物空心球具有良好的负热膨胀特性,在室温至200℃的温度区间内,负膨胀系数略低于理论值,平均热膨胀系数为-11.4×10-6K-1。     

原位反应固相法合成低热膨胀ZrW_2O_8/ZrO_2复合材料

以分析纯ZrO2、WO3为原料,采用分步焙烧-原位反应固相法成功合成了低热膨胀ZrW2、WO8/ZrO2复合材料,着重研究了不同烧结温度和烧结时间对产物的影响.通过X射线衍射仪(XRD)、扫描电镜(SEM)、能谱仪(EDS)和热膨胀仪对合成的ZrW2O8/ZrO2复合材料的晶体结构、断面形貌和热膨胀性能进行表征.研究结果表明,在1125、1150、1200℃烧结6h都可以合成高纯度的ZrW2O8/ZrO2复合材料,其组元为α-ZrW2O8和m-ZrO2相;随烧结时间的延长,衍射半峰宽逐渐减小,晶粒在不断长大,致密度相对提高;随着ZrW2O3质量分数增加,复合材料的热膨胀系数减小,其中25%(质量分数)ZrW2O8/ZrO2复合材料在30～600℃的平均热膨胀系数为0.2153×10-6K-1.     

ZrW_(1.5)Mo_(0.5)O_8薄膜的制备及其负热膨胀性能研究

以脉冲激光沉积法沉积制备了立方相负热膨胀ZrW1.5Mo0.5O8薄膜并利用X射线衍射仪(XRD)和场发射扫描电镜对其结构组分、表面形貌和厚度进行表征。采用变温XRD分析了ZrW1.5Mo0.5O8靶材和薄膜的负热膨胀特性。实验结果表明:在1080℃烧结6h制备得的立方相ZrW1.5Mo0.5O8陶瓷靶材,靶材具有较高的纯度和良好的负热膨胀性能,Mo离子掺入后,其α到β相转变温度降低,在30~600℃温度区间内,ZrW1.5Mo0.5O8陶瓷靶材的负热膨胀系数为-7.13×10-6K-1。利用该靶材在500℃时脉冲激光沉积的ZrW1.5Mo0.5O8薄膜为非晶态,薄膜表面平滑致密,厚度约为835nm;非晶膜在1180℃热处理7min后淬火得到立方相ZrW1.5Mo0.5O8薄膜;结晶后的ZrW1.5Mo0.5O8薄膜为多晶膜。在室温到600℃区间内,立方相ZrW1.5Mo0.5O8薄膜的热膨胀系数为-7.7×10-6K-1,α-ZrW1.5Mo0.5O8到β-ZrW1.5Mo0.5O8的相转变温度降至100℃以下。     

PVP对溶胶凝胶法制备负热膨胀ZrW_2O_8粉体形貌及性能的影响

以PVP为添加剂,采用溶胶凝胶法制备ZrW_2O_8粉体,研究添加剂对粉体形貌的影响及其负热膨胀特性。对其前驱体进行热重-差热分析(TG-DSC),以X射线粉末衍射(XRD),扫描电子显微镜(SEM)对产物结构及形貌进行表征。结果表明所得粉体为单一立方α-ZrW_2O_8相。加入PVP后,可以有效地改变粉体的形貌,随着加入量的增大,粉体的形貌从无规则的团聚体转变为长棒状、扇形及短棒颗粒。原位X射线粉末衍射分析表明,所得ZrW_2O_8粉体具有良好的负热膨胀特性。     

射频磁控溅射制备负热膨胀ZrW2O8薄膜的应力特性研究

采用ZrW2O8陶瓷靶材,以射频磁控溅射法在单晶硅基片上沉积制备了ZrW2O8薄膜。用X射线衍射仪和热膨胀仪分析了靶材的成分和热膨胀性能;用X射线光电子能谱仪和扫描电子显微镜分析了薄膜的组分及其表面形貌;用表面粗糙轮廓仪和薄膜应力分布测试仪测量了薄膜的厚度和应力。实验结果表明:制备的ZrW2O8靶材纯度高且具有良好的负热膨胀性能,磁控溅射沉积制备的ZrW2O8薄膜和靶材保持良好的化学成分一致性,且表面平滑、致密,在750℃热处理3 min后薄膜表面晶粒明显长大,并出现孔洞缺陷;衬底未加热时沉积制备的ZrW2O8薄膜选区应力差最小,应力分布最均匀,随着热处理温度和衬底温度的提高,由于薄膜和衬底的热膨胀系数的差异较大,薄膜选区内的应力差增加,薄膜应力分布不均性增大。     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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。     

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.