Y3+取代Bi3+对Bi2(Zn1/3Nb2/3)2O7陶瓷烧结温度的影响

采用固相反应制备Bi2(Zn1/3Nb2/3)2O7微波陶瓷,并借助X射线、扫描电镜、LCR4284测试仪,研究Y3 取代Bi3 对Bi2(Zn1/3Nb2/3)2O7陶瓷烧结特性及介电性能的影响。研究结果表明:随着Y3 替代量的增加,晶粒尺寸减小,介电常数先减小后增大,烧结温度升高;适量的Y3 替代可以获得性能很好的BZN介质材料。     

(Bi_(1/2)Na_(1/2))_(1-x)Ba_xTiO_3系无铅压电陶瓷的现状

综述了(Bi1/2Na1/2)1-xBaxTiO3系无铅压电陶瓷的最新研究进展。简述了A位非化学计量改性及几种较成功的掺杂改性方法。将A位掺杂(如La3+)、B位掺杂(如Co3+、Nb5+)以及综合掺杂(如Ce3+、Ce4+)的优缺点和掺杂机理进行了归类比较。解释了各系统中相应掺杂引起性能变化的原因,为进一步开展无铅压电陶瓷的研究提供参考。     

Solvothermal Synthesis and Photocatalytic Performance of Bi_2S_3 Hierarchical Nanostructure

The synthesis of Bi_2S_3 hierarchical nanostructure was reported by a solvothermal reaction using ethylene disulfhydrate as the sulfur source and chelating reagent. The as-synthesized samples were characterized by X-ray diffraction(XRD), Raman, X-ray photoelectron spectroscopy(XPS), scanning electron microscopy(SEM) and photoluminescence(PL). The XRD, Raman, and XPS data confirmed that the as-synthesized sample belongs to orthorhombic phase Bi_2S_3. The SEM observations displayed that Bi_2S_3 hierarchical nanostructure assembled from nanorods. A 410 nm ultraviolet photoluminescence(PL) emission of as-synthesized Bi_2S_3 was observed when the sample was excited with wavelength of 320-330 nm. The Bi_2S_3 hierarchical nanostructure also shows a significant enhancement of photocatalytic capability toward degrading methyl orange(MO) under UV light, the photodegradation of MO reaches 95% within 180 min.     

Electrodeposition and characterization of thermoelectric Bi_2Se_3 thin films

Bi2Se3 thin films were electrochemically deposited on Ti and indium tin oxide-coated glass substrates,respectively,at room temperature,using Bi(NO3)3·5H2O and SeO2 as starting materials in diluted HNO 3 solution.A conventional three-electrode cell was used with a platinum sheet as a counter electrode,and a saturated calomel electrode was used as a reference electrode.The films were annealed in argon atmosphere.The influence of cold isostatic pressing before annealing on the microstructure and thermoelectric...     

Bi_(1,7-X)Pb_(0.3)Sb_xSr_2Ca_2Cu_3O_(10)的制备及超导电性研究

本文采用差热分析研究了Bi_(1,7-x)Pb_(0.3)Sb_xSr_2Ca_2Cu_3O_(10)(x=0.05;0.10;0.15;0.20)系统的烧结工艺,研究了元素Sb的置换对该体系超导电性的影响,少量Sb的置换有利于110K相的快速生成,减少反应时间,同时,由于Sb~(3+)的离子半径小于Bi~(3+),置换量过大则会导致大量的杂相生成而降低体系的T_c.     

Rare Earth Ion Yb~(3+) Doping of Bi_2WO_6 with Excellent Visible-light Photocatalytic Activity

The rare earth ion Yb~(3+) doped Bi_2WO_6 photocatalysts were synthesized by hydrothermal method.Moreover,XRD,XPS,FESEM,TEM,Ramam,N_2 adsorption-desorption isotherm measurements and UV-vis diffusion reflectance spectra were used to characterize the Yb~(3+) doped Bi_2WO_6 photocatalysts.The morphology,specific surface area,and pore volume distribution were greatly affected after Yb~(3+) ions doping.Photocatalytic performance of Bi_2WO_6 was effectively enhanced after Yb~(3+) ions doping,6% Yb~(3+) doped Bi_2WO_6 had the best photocatalytic performance,and 96.2% Rhodamine B was degradated after irradiated 30 min,which was 1.29 times that of the pristine one.The enhanced photocatalytic performance was due to the increased specific surface area,decreased energy band gap and inhibition of photoelectron-hole recombination after Yb~(3+) ions doping.     

Electronic Structure and Transport Coefficients of the Thermoelectric Materials Bi_2Te_3 from First-principles Calculations

The electronic structures of bulk Bi_2Te_3 crystals were investigated by the first-principles calculations.The transport coefficients including Seeback coefficient and power factor were then calculated by the Boltzmann theory,and further evaluated as a function of chemical potential assuming a rigid band picture.The results suggest that p-type doping in the Bi_2Te_3 compound may be more favorable than n-type doping.From this analysis results,doping effects on a material will exhibit high ZT.Furthermore,we can also find the right doping concentration to produce more efficient materials,and present the "advantage filling element map" in detail.     

Structure of Bi2O3-ZnO-B2O3 system low-melting sealing glass

Bi_2O_3-ZnO-B_2O_3 system glass is a kind of lead-free low melting sealing glasses. The structure of Bi_2O_3-ZnO-B_2O_3 system low-melting sealing glass was investigated by DSC, FT-IR, XRD and SEM. The results show that with the increase of B_2O_3 content, the transition temperature Tg and softening temperature T_f of Bi_2O_3-ZnO-B_2O_3 system low-melting sealing glasses increase, which leads to the liquid phase precipitation temperature increasing and promotes the structure stability in the glass. With increasing the heat treatment temperature, a large number of liquid phases appear in samples and the sinter efficiency of the samples increases. The FT-IR spectra of the glasses show the presence of some bands that are assigned to vibrations of Bi-O bond from [BO_3] pyramidal and [BiO_6] octahedral units and B-O from [BO_3] and [BO_4] units. With the decrease of B_2O_3 content, the crystallization tendency of the glass increases. In glass samples B_1 and B_2, crystallization starts at 460 ℃ and 540 ℃, respectively. Both of them precipitate Bi-(24)B_2O_(39) phases.     

SYNTHESIS AND X-RAY POWDER STUDY OF A NEW COMPOUND:Ba_6Ti_7Nb_9O_(42)

A new compound Ba6Ti7Nb9O42 was prepared for the first time by solid state reaction in BaO-TiO2-Nb2O5, ternary system. The X-ray powder diffraction data of the title compound was determined. Ba6Ti7Nb9O42 crystallizes in the hexagonal system -with unit cell parameters a=9.0527(4) A,c=11.790(1) A,and space group P63/mcm(193),z=1. The calculated and measured densities are 5. 293 g/cm3 and 5.285 g/cm3, respectively.     

p型Bi2Te3/CoSb3系结构梯度热电材料性能研究

采用放电等离子烧结法制备了 Bi2 Te3/ Co Sb3二元梯度热电材料。 SEM分析结果表明 :均质材料 Bi2 Te3和Co Sb3在界面处结合紧密。当热端和冷端的温度分别保持在 80 0 K和 30 0 K时 ,分别对 2种均质材料的界面结合处的温度和长度进行了计算和设计 ,得出梯度热电材料界面结合处的最佳温度约为 5 0 0 K,相应的 Bi2 Te3和 Co Sb3长度分别为1.2 mm和 10 m m。同时通过对梯度热电材料的赛贝克系数和功率因子的研究发现 :梯度热电材料的赛贝克系数相对于均质材料在一个较宽的温度范围内具有较高的数值 ;在 36 0～ 4 6 0 K的温度范围内 ,梯度热电材料具有较 2种均质材料Bi2 Te3和 Co Sb3高的功率因子     

Preparation of BN／SiO2 ceramics by PIP method

The precursor infiltration and pyrolysis(PIP) method for preparation of BN/SiO2 composites was used to improve mechanical properties, dielectric properties and feasibility of high temperature dielectric parts with large dimensions and complex shapes. In the processing procedure, the porous BN ceramic matrix was first successfully prepared by compacting the mixed powders of B and BN and then sintering them at a certain temperature under normal pressure of N2. The polycarbosilane(PCS) solution was vacuum infiltrated into porous BN ceramics at the room temperature and then at 800℃ in the air to depolimerize out amorphous SiO2, and sintered further at 1 300℃ in N2 to get BN/SiO2 composites. The microstructure of materials was studied by means of X-ray diffraction and electron probe micro analysis. The thermo-decomposition mechanism of PCS was investigated by a TG-DTA and infrared (IR) spectrum analysis. The flexural strengths were measured by the three-point bending method. The dielectric constant and the loss tangent were measured by the wave-guide method. The results show BN/SiO2 composites were fabricated. The obtained composites posses a flexural strength of 61.96 - 93.31 MPa, the dielectric constant in the range of 3.50 - 3.78 and the order of magnitude of the loss tangent at 10^-3 , which are good for the high tempera turedielectric parts with large size and complex shapes.     

Effect of Al_2O_(3np) on the Properties and Microstructure of B_4C_p/Al Composites

Aluminum-matrix boron carbide (B_4C_p/Al) is a kind of neutron absorbing material widely used in nuclear spent fuel storage.In order to improve the tensile property of B_4C_p/Al composites,a new type of nano-Al_2O_3 particle (Al_2O_(3np)) reinforced B_4C_p/Al + Al_2O_(3np) composites were prepared by powder metallurgy method.The Monte Carlo particle transport program (MCNP) was used to determine the influence of Al_2O_(3np )on the thermal neutron absorptivity of composites.The universal material testing machine and scanning electron microscope (SEM) were used to study the mechanical properties,microstructure and fracture morphology of B_4C_p/Al composites.The results indicated that the neutron absorption properties of B_4C_p/Al composites were not affected by the addition of nano-Al_2O_3 particles in the range of 1 wt%-15 wt%.The addition of Al_2O_(3np) can obviously reduce the grain size of B_4C_p/Al matrix metals thus improve the tensile strength of the composites.The addition threshold of Al_2O_(3np) is about 2.5 wt%.Both B_4C_p and Al_2O_(3np) change the fracture characteristics of the composites from toughness to brittleness,and the latter is more important.     

La2O3掺杂对(Bi1/2Na1/2)0.94Ba0.06TiO3陶瓷性能与微结构的影响

采用传统陶瓷工艺方法制备了La2O3掺杂(Bi1/2Na1/2)0.94Ba0.06TiOa(BNBT6)无铅压电陶瓷,系统地研究了La2O3掺杂对该体系陶瓷介电、压电性能与微观结构的影响.结果表明:该体系具有很高的压电常数,是单一的钙钛矿结构,La2O3的添加对晶粒生长具有一定的抑制作用,线收缩率和相对密度增大.室温介电常数随着La2O3掺杂量的增加而增大.与不添加La2O3的陶瓷样品相比,添加少量La2O3可以使体系的弛豫特征更为明显.当掺杂量为0.1 wt%时,该体系陶瓷具有较好的综合性能:d3a=160 pC/N,kp=0.322.当掺杂量达到0.5 wt%以后,陶瓷的压电性能严重降低.     

BaZrO3颗粒分散混合导体YBa2Cu3O7-δ的微结构与性能研究

通过在YBa2Cu3O7-δ的起始原料中直接掺入过量的BaO和等摩尔ZrO2,原位生成均匀弥散分布的BaZrO3第二相颗粒的方法制备YBa2Cu3O7-δ-BaZrO3复合混合导体材料.研究了引入第二相BaZrO3颗粒对基相YBa2Cu3O7-δ的微观结构、热膨胀行为和力学性能的影响.发现弥散的BaZrO3颗粒能有效地抑制YBa2Cu3O7-δ沿C轴方向的生长,使晶粒由条形变为方形.与YBa2Cu3O7-δ单相样品相比,含10 mol%BaZrO3颗粒的样品具有更高的相对密度和较低的热膨胀系数以及显著改善的力学强度.     

Sol－Gel法制备YBa_2Cu_3O_（7－x）超细粉末研究

用柠檬酸盐作螯合剂，用氨水调节溶液的酸度，通过Ｓｏｌ－Ｇｅｌ转变制得了粒径为１００ｎｍ大小的ＹＢａ２Ｃｕ３Ｏ（７－ｘ）超细粉末，对ＹＢａ２Ｃｕ３Ｏ（７－ｘ）在合成反应中溶胶的形成和凝胶聚合过程进行了研究和探讨。Ｓｏｌ－Ｇｅｌ法制得的ＹＢａ２Ｃｕ３Ｏ（７－ｘ）超细粉末在粒度、纯度、烧结特性和超导性能上，均优于固态反应合成方法。     

Solid Solution Characteristics of Pb（B1/3Nb2/3）O3-bascd Composite Ceramics

The solid solution characteristics of Pb(B1/33Nb2/3)O3-based(B=Zn2+,Mg2+,Ni2+)composite ceramics prepared by two-phase mixed-sintering method were developed based on dielectric measurements.Results show that there are double dielectric peaks for PZN-based composite ceramic,implying two phases coexist.However single dielectric peak was presented in PMN-and PNN-based composite ceramics,respectively.It is indicated that obvious solid solution reaction exists during the sintering process of these two systems.The effects of B-site ion difference on the solid solution characteristics were discussed by crystal chemistry.SEM was employed to investigated the microstructures of composite ceramics.The influences of solid solution reaction on grain growth were discussed.     

Microstructure and Dielectric Property of 3D BN_f/Si_3N_4 Fabricated by CVI Process

As potential wave-transparent materials applied at high temperatures, 3D BN_f/Si_3N_4 ceramic matrix composites were prepared by low pressure chemical vapor infiltration or deposition(LPCVI/CVD) process from SiCl_4-NH_3-H_2-Ar gas precursor at 800 oC. The densification process, microstructure and dielectric properties of 3D BN_f/Si_3N_4 composites were investigated. The results indicated that 3D BN_f/Si_3N_4 was successfully fabricated by LPCVI/CVD, with final open porosity of 2.37% and density of 1.89 g/cm~3. Densification kinetics of 3D BN_f/Si_3N_4 is a typical exponential pattern. The Si_3N_4 matrix was uniformly infiltrated into porous BN_f preform. The deposited Si_3N_4 matrix was amorphous by XRD analysis. Introduction of BN fiber into Si_3N_4 ceramic lowered the permittivity of Si_3N_4. The fabricated BN_f/Si_3N_4 composites possess low permittivity of 3.68 and low dielectric loss of lower than 0.01, which are independent of temperature below400 oC. Transmission coefficient of BN_f/Si_3N_4 composite is 0.57 and keeps stable below 400 oC. BN_f/Si_3N_4 can be fabricated at low temperature and may be candidates for the microwave transparent materials.     

STUDY ON PREPARATION OF YBa_2Cu_3O_(7-x) ULTRAFINE POWDERS BY SOL-GEL PROCESS

The ultrafine powders of YBa_2Cu_3O_(7-x) withthe size of 100nm were synthesized by Sol-Gel process using cit-rate as complex and ammonium hydroxide to adjust pH of solu-tion. The process of Sol formation and Gel polymerization ofYBa_2Cu_3O_(7-x) in the Sol-Gel synthetic reaction has bee studied.The particle size,pruity,sintering activity and superconductingproperties of YBa_2Cu_3O_(7-x)prepared by Sol-Gel method are betterthan by solid state reaction.     

Fe 2(SO4)3/SiO2 催化合成环己酮1,2-丙二醇缩酮

采用溶胶-胶凝法和浸渍法制备了二氧化硅负载的硫酸铁[Fe₂(SO₄)₃/SiO₂]固体酸催化剂,以环己 酮和1,2-丙二醇为原料,在无溶剂条件下合成了环己酮1,2-丙二醇缩酮。考察了Fe₂(SO₄)₃/SiO₂ 固体酸催化剂 的焙烧温度、Fe₂(SO₄)₃ 在SiO₂ 上的负载量、醇酮物质的量比、催化剂质量和反应时间等因素对产品收率的影响。 实验结果表明,Fe₂(SO₄)₃/SiO₂ 固体酸是合成环己酮1,2-丙二醇缩酮的理想催化剂,较适宜的反应条件为:催化 剂的焙烧温度300℃、Fe₂(SO₄)₃ 在SiO₂ 上的负载量20%、环己酮与1,2-丙二醇的物质的量比1∶1、催化剂质量 分数5%和反应时间70min。在此条件下,环己酮1,2-丙二醇缩酮收率达到98.21%。Fe₂(SO₄)₃/SiO₂催化剂具 有良好的稳定性,重复使用5次后环己酮1,2-丙二醇缩酮的收率为88.90%。     

Synthesis and characterization of layered perovskite-type organic-inorganic hybrids (R-NH3)2(CH3NH3)Pb2I7

Layered organic-inorganic hybrids containing bilayer perovsikte (R-NH3)2(CH3NH3)Pb2I7 (where R=C12H25,C6H5C2H4) were synthesized by reactions in solution. The influences of the solvents and the reactant ratio on the structures of the products were investigated. The structures and the properties of the hybrids were characterized using X-ray diffraction (XRD) and ultraviolet and visible (UV) adsorption spectra. For comparing with the bilayer perovskite hybrids in structure and band gap magnitude, the hybrids containing monolayer perovskite (R-NH3)2PbI4 were also synthesized and characterized. The results demonstrate that the thickness of inorganic layer has obvious effect on the tunneling magnitude of the band gap but the organic part can be micro actuator of band gap.