材料期刊网

Effect of Sn4+ B-Site Substitution on the Microstructure and Dielectric Properties of Ba(Mg1/3Ta2/3)O3 Microwave Ceramics

Shunhua WU , Guoqing WANG , Shuang WANG , D , an LIU

材料科学技术（英文）

The effect of Sn4+ (BaSnO3) B-site substitution on the microstructure and dielectric properties of Ba(Mg1/3Ta2/3O3 microwave ceramics was investigated. X-ray diffraction shows that a complex perovskite material Ba(Mg1/3Ta2/3)O3 was prepared. As Sn4+ content x increases in the (1-x) Ba(Mg1/3Ta2/3)O3-xBaSnO3 (x=0.00～0.20) system, the dielectric constant generally keeps unchanged, while TCF changes from positive to negative. Although the addition of Sn4+ reduces the ordering degree, Qf0 is still increased when the ceramics density increases. This trend implies that Qf0 of this system is mostly determined by ceramics density rather than ordering degree. After sintering at 1500℃ for 3 h, the system with x=0.15 was found to have excellent dielectric properties as follows: ε≈25, Qf0≥300,000 GHz at 7 GHz, TCF=-0.6×10-6℃.

关键词: Ba(Mg1/3Ta2/3)O3 , null , null , null

Energy levels of the d*(8) electron and d*(2) hole system

Physical Review B

In the investigation of the optical and magnetic properties of the semiconductors containing transition-metal ions, the one-electron orbital cannot be treated with a pure d orbital because of a strong covalence. This paper presents the energy matrix of the d*(8) and d*(2) (d* means a modified d function) system, in which the covalence is described by two covalent factors. The differences between the matrix diagonal elements of the t(2)(m)e(n) term of the d*(8) system and the t(2)(6-m)e(4-n) term of the d*(2) system vary with m and n. The d(N) electron system can be explained with the d(10-N) hole system because the difference between the energy matrix of the d(N) and d(10-N) systems has a fixed value. However, this kind of simple relation does not exist for the d*(N) and d*(10-N) systems when the covalence is considered. A numerical calculation shows that the variation of the energy levels with the covalence for Ni2+ in the d*(8) electron system is larger than that in the d*(2) hole system. The calculated energy levels obtained from the d*(8) matrix are in good agreement with the experimental data of the Ni2+ ion for ZnS:Ni and ZnSe:Ni. This suggests that the d*(8) electron system instead of the d*(2) hole system should be used in the investigation of optical and magnetic properties of semiconductor containing Ni2+ ions.

关键词: zns-ni;absorption;vanadium;impurities;spectra;ions

液晶材料与3D显示

张兴 , 郑成武 , 李宁 , 周兴丹 , 李正强 , 华瑞茂

液晶与显示 doi:10.3788/YJYXS20122704.0448

介绍了3D显示的基本原理,重点介绍了目前3D显示的主流技术类型,包含了眼镜式3D技术以及裸眼式3D技术,其中眼镜式3D技术包含色差式3D技术、偏光式3D技术和主动快门式3D技术;裸眼式3D技术包含视差屏障式3D技术、柱状透镜式3D技术、指向光源式3D技术和多层显示式3D技术.阐述了各种3D显示技术的基本实现原理和应用领域、并对涉及液晶显示的几种3D技术的优缺点进行了对比.结合液晶材料的特点与3D液晶显示的实际要求,阐述了3D液晶面板对液晶材料快速响应方面的要求,以及液晶透镜对液晶材料光学各向异性参数的要求.

关键词: 3D显示 , 眼镜式3D显示 , 裸眼式3D显示 , 液晶材料

COMPARISON OF FATIGUE AND CREEP BEHAVIOR BETWEEN 2D AND 3D-C／SiC COMPOSITES

D.Han , S.R.Qiao , M.Li , J.T.Hou , X.J.Wu

金属学报(英文版)

The differences of tension-tension fatigue and tensile creep characters of 2D-C/SiC and 3D-C/SiC composites have been scrutinized to meet the engineering needs. Experiments of tension-tension fatigue and tensile creep are carried out under vacuum high temperature condition. All of the high temperature fatigue curves are flat; the fatigue curves of the 2D-C/SiC are flatter and even parallel to the horizontal axis. While the tension-tension fatigue limit of the 3D-C/SiC is higher than that of the 2D-C/SiC, the fiber pullout length of the fatigue fracture surface of the 3D-C/SiC is longer than that of the 2D-C/SiC, and fracture morphology of the 3D-C/SiC is rougher, and pullout length of the fiber tows is longer. At the same time the 3D-C/SiC has higher tensile creep resistance. The tensile curve and the tensile creep curve of both materials consist of a series of flat step. These phenomena can be explained by the non-continuity of the damage.

关键词: 2D-C/SiC , null , null

Surface properties of 3d transition metals

Philosophical Magazine

Using the projector augmented wave method within density functional theory, we present a systematic study of the layer relaxation, surface energy and surface stress of 3d transition metals. Comparing the calculated trends for the surface energy and stress with those obtained for 4d and 5d metals we find that magnetism has a significant effect on the surface properties. Enhanced surface magnetic moments decrease the size of the surface relaxation, lower the surface energy and surface stress, leading to compressive stress in Cr and Mn.

关键词: surface relaxation;surface energy;surface stress;magnetic transition;metals;density functional theory;full charge-density;initio molecular-dynamics;total-energy;calculations;augmented-wave method;ab-initio;electronic-structure;atomic volume;work function;basis-set;relaxation

R&D STATUS ON INTERMETALLICS IN CHINA

CHEN Guoliang(State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing 100083 , China)SHI Changxu (Academia Sinica , Beijing 100864 , China)

金属学报(英文版)

This paper briefiy introduces the R&D of intermetallics in China. R&D on intermetallics in a national scale in China began near ten years ago. The investigation in past years focused on the fundamental research and materials development. A significant progress has been made. Various components that made of Ti3Al Ni3Al, TiAl and Fe3Al have been successfully manufactured Some of them have been evaluted. It is expected that some intermetallic alloys will be produced in an industrial scale in the near future.

关键词: :intermetallic alloys , null , null , null

R & D ACTIVITIES ON AEROSPACE MATERIALS IN KOREA

H.M. Kim(Korea Institute of Machinery and Materials , Korea Manuscript received 26 August 1996)

金属学报(英文版)

This paper briefly reviews research and development programs in Korean aerospace industry,with an emphasis on aircraft materials technology. International collaborations in these areas are outlined and the R & D activities are highlighted against the　background of the national economy.It is shown that the investment from government agencies and large enterprises has led to healthy development of aerospace materials industries in Korea.

关键词: :R & D , null , null , null

陶瓷3D打印技术综述

杨孟孟 , 罗旭东 , 谢志鹏

人工晶体学报

本文介绍了陶瓷3D打印技术目前的发展状况、主要的成型技术和重要的应用领域，重点介绍3D打印技术在陶瓷方向的应用。回顾了可适用于直接三维打印和立体光固化法打印的氧化物( Al2 O3、ZrO2)和非氧化物( Si3 N4、SiC)陶瓷浆料的最新研究成果及成型技术对制品性能的影响，并展望了陶瓷3D打印技术未来的发展方向。

关键词: 3D打印 , 陶瓷 , 浆料 , 成型技术

Size dependence of electrical resistivity 1D-layered nanostructures

Nanostructured Materials

The Landauer electrical resistivity R of one-dimensional (1D) layered nanostructures is calculated. The analysis of the logarithm of the resistance as a function of grain size reveals that there is a minimum value of resistivity R(min) when the grain size takes a value of d(c), where d(c) depends on the barrier height and excess volume of interface. R increases in the region of d(cl) > d > d(c), where d is the grain size, and d(cl) is another critical value of grain size. The mechanism of the anomalous resistivity behavior is discussed briefly.

关键词: nanocrystalline;resistance;alloys

D-D中子发生器n-γ密度测井的蒙特卡罗模拟研究

何雄英 , 徐大鹏 , 谢芹 , 卢小龙 , 郑世平 , 姚泽恩 , 兰长林

原子核物理评论 doi:10.11804/NuclPhysRev.30.02.151

根据D-D反应中子的能谱和角分布数据，建立了中子源模型；根据石灰岩地层标准刻度井群数据，建立了井模型。采用MCNP程序模拟了井中中子和γ射线的输运，得到了不同地层密度和不同源距处NaI探测器中的混合γ射线能谱和非弹γ射线能谱。在混合γ射线能谱2.5～5.0 MeV能区开窗，研究了开窗区混合γ射线相对计数随源距的变化关系，确定源距应选择在30～80 cm范围，给出了密度与混合γ射线计数之间的非线性关系。研究表明，可以利用D-D中子源的混合γ射线能谱来实现n-γ密度测井。

关键词: 密度测井 , D-D中子源 , 蒙特卡罗模拟 , 石灰岩