Core-Shell Structures in ZrO2-Modified BaTiO3 Ceramic

Pure BaTiO₃ exhibits a paraelectric-to-ferroelectric phase transition at 130°C. When stoichiometric BaTiO₃ is combined with 10 mol% ZrO₂, the relative permittivity (ε) changes to a broad, relatively insignificant temperature dependence, and the Curie point, T _c , is not sharply defined. However, the transition sharpens at T = 95°C when these samples are sintered for a longer period of 60 h. SEM, EDAX analysis coupled with TEM observation gives three types of core-shell structures of different microstructural characteristics which are related to the diffuse phase transition. Chemical inhomogeneity, due to Zr⁴⁺ distribution in the core-shell structure, is proposed to account for the diffuse phase transition behavior.     

Lanthanum-Magnesium and Lanthanum-Manganese Donor-Acceptor-Codoped Semiconducting Barium Titanate

BaTiO₃ powder doped with La donor and codoped with Mn or Mg acceptor was sintered at 1350°C/1 h in air. For Ladoped BaTiO₃, the room-temperature resistivity decreased to a minimum at [La³⁺] ∼ 0.15 mol%. For La-Mn-codoped BaTiO₃, the minimum resistivity occurred at [La³⁺] - 2[Mn²⁺] ∼ 0.15 mol%. When the ceramic was changed to a fine-grained insulator by high donor doping ([La³⁺] >0.15 mol%), its semiconductivity was restored, and the relatively homogeneous, coarse-grained microstructure recurred by codoping with either Mg or Mn acceptor, with the transition at [La³⁺] - 2[Mg²⁺] = 0.15 mol% or [La³⁺] - 2[Mn²⁺] = 0.15 mol%. The analogy of a compensation effect between La-Mn- and La-Mg-codoped BaTiO₃ suggested that Mn acceptor added to BaTiO₃ exists as Mn²⁺ ion in the bulk grain region; its influence on the positive temperature coefficient of resistivity behavior is then discussed.     

含盐异丙醇溶液饱和蒸汽压的测定和关联

<正>为了考察电解质-盐类对汽液平衡的影响,研究挥发性溶剂在不同盐浓度下的饱和蒸汽压与温度的关系,对于理论上了解盐效应的机理,实践中用于恒沸混合物的加盐精馏、有机生物物料的制取分离等都是很有意义的.由丙烯水合制异丙醇的传统过程是得到异丙醇和水的恒沸物,而后再加入第三组分进行特殊精馏,便可得到无水异丙醇.近年来人们试探改革这一传统过程,运用加盐萃取精馏.这是因为盐效应可较大地改变各组分的相对挥发度,以致消除恒沸.由于氯化锌较其他盐(如CaCl_2)在异丙醇中有较大的溶解度,并有较大的溶解速率,因此研究ZnCl_2-异丙醇溶液的饱和蒸汽压是有现实意义的.     

高密度及多组元方阱位能混合物流体的计算机Monte Carlo模拟

<正>流体的热力学宏观性质由其微观结构所支配,因此许多研究者用计算机Monte Carlo模拟(MC)或分子动力学模拟(MD)方法,力求得到流体的微观结构的真实图象,并据此建立推算或预测流体宏观性质的热力学模型.     

新铌酸盐化合物K4CuNb8O23及其Cu^2＋与Nb^5＋的类质同象代换

1986年Wanklyn等曾报道存在化合物K_5Cu_2Nb_(11)O_(31),并给出其X射线粉晶谱线,但未见进一步指标化和确定其所属晶系及晶胞参数的报道。本研究表明,存在一种新铌酸盐晶体K_4CuNb_8O_(23),其成分及X射线谱异于K_5Cu_2Nb_(11)O_(31)。 用分析纯K_2CO_3、Nb_2O_5及CuSO_4·5H_O按一定比例配制并于1100—1300℃间烧成,     

基于临时安全域的网格安全认证模型的研究

分析了现有网格安全体系结构模型存在的问题,结合网格固有的特点设计了一个网格环境下的认证模型,该模型以虚拟组织和信任域为基础,针对域内和域间环境采用不同的认证策略并且引入了临时安全域(TSD)的概念,通过分析表明该模型在提供安全身份鉴别的同时简化了实体之间的认证,满足网格环境的安全需求。     

下一代SDH传送网的关键技术

介绍支持数据业务的下一代同步数字体系(SDH)所用关键技术(通用成帧规程(GFP)、虚级联(VC)和链路容量调整方案(LCAS))的主要技术特点,比较了使用VC技术前后的带宽利用率;重点阐述LCAS帧结构各字节的含义及其表示方法,介绍LCAS的实现方式和链路容量调整的详细过程;最后分析LCAS技术在自动交换光网络(A-SON)中的作用及商用实例。LCAS与VC、GFP结合,能使新一代SDH网络更好地支持二层交换业务,全面适应数据业务的需求,在现有传输网上实现ASON的某些功能,逐渐过渡到智能光网络。     

Wet-chemical etching of (11 $$\bar 2$$ 0) ZnO films0) ZnO films

This paper describes the optimized process of wet-chemical etching of a ZnO film grown on an r-plane sapphire. Different etchants and solution ratios have been used to achieve controllable etching rate and steep etching profile. With selected etching solutions, the etching profiles of epitaxially grown ZnO films (>1.3 μm) are improved. Using Al instead of photoresist as the mask generates a steeper etching slope. Maximal 1:1 vertical/horizontal ratio (45°) has been achieved. X-ray photoelectron spectroscopy (XPS) and sheet resistance measurements show that this wet-chemical etching process has negligible influence on the modification of the physical and chemical properties of the etched surface.     

A 32-GHz non-uniform distributed amplifier in 0.18-/spl mu/m CMOS

This letter presents a fully integrated distributed amplifier in a standard 0.18-/spl mu/m CMOS technology. By employing a nonuniform architecture for the synthetic transmission lines, the proposed distributed amplifier exhibits enhanced performance in terms of gain and bandwidth. Drawing a dc current of 45mA from a 2.2-V supply voltage, the fabricated circuit exhibits 9.5-dB pass-band gain with a bandwidth of 32GHz while maintaining good input and output return losses over the entire frequency band. With a compact layout technique, the chip size of the distributed amplifier including the testing pads is 940/spl times/860/spl mu/m/sup 2/.