Journal of Alloys and Compounds
As hydrogen, deuterium and tritium storage materials, a series of investigations of mechanical and thermal properties of titanium hydrides, deuterides and tritides have been performed, however, very limited theoretical studies of thermodynamic properties for them can be found. Based on density-functional theory (DFT) and density-functional perturbation theory (DFPT) we have discussed systematically the hydrogen isotope effects on the thermodynamic properties of TiX2 (X = H, D, and T) system. Our calculations indicate that for evaluating accurately their physical properties at absolute zero temperature, such as the equilibrium lattice constants, bulk modulus, and heat of formation, the zero-point energy correction must be taken into account. By performing the phonon calculation within quasiharmonic approximation (QHA), we obtain their vibrational free energies, vibrational entropies, and temperature dependence of specific heat, thermal expansion, and bulk modulus. Those results demonstrate that comparing with TiH2, TiT2 and TiD2 are more stable and the zero-point effects play an important role in their thermal expansion. The increase in the force constant between Ti and H causes the higher value of specific heat of TiH2 during the phase transition from FCC to FCT. In addition, comparing with available experimental values, we can conclude that QHA is feasible for describing the thermal properties of TiX2. (C) 2006 Elsevier B.V. All rights reserved.
关键词:
isotope effects;thermodynamic properties;density-functional;perturbation theory;quasiharmonic approximation;functional perturbation-theory;neutron spectroscopy;thermal-properties;titanium;hydrogen;dependence;expansion;constants;palladium;hydrides
张昕
,
周鑫
,
张红
原子核物理评论
采用4GyX射线辐照人乳腺癌细胞MCF-7,分别在照射后0,2,4,8,16,24,48,72和144h时间点收集细胞,提取DNA并以聚合酶链式反应进行扩增,再以BsaXI限制性内切酶对扩增产物进行消化,消化产物以琼脂糖凝胶电泳进行分离.结果表明,4GyX射线辐照可引起D310片段突变,且该突变在经辐照之后144h检测水平明显超过野生型.
关键词:
X射线辐照
,
线粒体DNA损伤
,
D310片段突变
,
聚合酶链式反应
朱杰武
,
柳永宁
,
许雁
,
冯耀荣
机械工程材料
doi:10.3969/j.issn.1000-3738.2005.06.007
在不同温度下测试了X70管线钢动态断裂韧度K1d、J1d和止裂韧度K1a以及夏氏V型缺口冲击韧度Ak,对三者的关系进行了分析.结果表明:温度和加载速率都对断裂韧度产生影响;加载速率变化引起的韧-脆断裂转变具有热激活特征,在热激活分析基础上,在应力强度因子速率K=15 MPa·m1/2s-1条件下,得出断裂韧度、止裂韧度和冲击韧度三者的关系:Ak=4.84×106T-2.8K1d(或K1a).可以用小试样Ak数据计算得到K1d和K1a.
关键词:
管线钢
,
断裂韧度
,
止裂韧度
,
韧-脆断裂转变
陈永亮
,
崔雅静
,
杨烨
,
王磊
,
李仪成
,
张勇
,
赵勇
低温物理学报
通过在SmFeAsO中Fe位上掺入5d过渡金属Ir,得到了一种新的铁基超导体SmFe_(1-x)Ir_xAsO,当x=0.05时,样品表现出超导电性,超导转变温度为8K,当x=0. 15时,超导转变温度达到最大值17. 3K X射线衍射结果表明所有样品均属四方ZrCuSiAs-type结构,SEM结果表明SmFe_(1-x)Ir_xAsO样品具有片层状形貌特征,随着Ir掺杂量的增大,晶格参数a增大而c减小,结合EDX数据,表明Ir掺人了SmFeAsO晶格当中.
关键词:
铁基超导体
,
ZrCuSiAs结构
魏恺文
,
王泽敏
,
曾晓雁
金属学报
doi:10.11900/0412.1961.2015.00212
利用OM, SEM, EDS, XRF和XRD等方法研究了AZ91D镁合金在激光选区熔化中的元素烧损机制以及烧损对成形试样化学成分、显微组织及力学性能的影响. 结果表明, 成形试样中Mg的相对含量(86.61%~88.68%)低于粉末原料中Mg的相对含量(90.63%), 而其Al的相对含量(10.40%~12.56%)则高于后者(8.97%). 该结果与基于Langmuir模型的计算结果相符, 表明在激光作用下主要是Mg发生了烧损. 成形试样的Mg与Al质量比η随激光体能量密度EV的增加呈现先上升后下降并最终趋于稳定的演变规律. 采用55.6 J/mm3的EV所成形试样(试样No.8)的η值最接近粉末原料. 使用回归分析法建立了η与EV的解析关系, 其拟合度指标系数R2为0.858. 成分变化最为显著之一的成形试样No.1 (采用166.7 J/mm3的EV所成形)与压铸态AZ91D 的组织特征相似, 均为β-Mg17Al12相呈网状分布于α-Mg基体间的典型凝固组织. 但成形试样No.1的β-Mg17Al12相含量及其α-Mg基体中Al的固溶量明显高于压铸态AZ91D. 成分变化导致成形试样No.1的拉伸强度及显微硬度得到提升, 但使其延伸率有所下降.
关键词:
激光选区熔化
,
AZ91D镁合金
,
元素烧损
,
化学成分
,
显微组织
,
力学性能
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
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
Powder Diffraction
The structure transitions and phase relationships of DyFe(3-x)Al(x) compounds have been investigated by X-ray powder diffraction. Our XRD results show that each of the compounds with x <= 0.45 crystallizes in the rhombohedral PuNi(3)-type structure with space group R (3) over barm and Z=9; for the 0.8 <= x<1.0 compounds, each has a hexagonal structure of the CeNi(3) type with space group P6(3)/mmc and Z=6; and each of the samples with 0.45<x<0.8 is a two-phase mixture of the PuNi(3)- and CeNi(3)-type structures. The calculated XRD intensities of the DyFe(3-x)Al(x) compounds with x=0.2, 0.33, 0.4, and 0.45 indicate that Dy occupies the 3a and 6c sites, Fe and Al distribute randomly on the 18h site, and the 3b and 6c sites are exclusively occupied by Fe, which agrees well with those of our experimental XRD patterns. The XRD intensities of the DyFe(3-x)Al(x) compounds with x=0.8 and 1.0 have also been calculated and found to agree with the experimental results with Dy on the 2c and 4f sites, Fe and Al at the 12k site, and Fe at the 2a, 2b, and 2d sites. In the two-phase region with x=0.45-0.8, the values of unit-cell parameters and phase compositions are linearly dependent on the value of x, indicating that the two phases are constituted by the same composition x with different stacking arrangements. This abnormal two-phase equilibrium is further confirmed by the structural analysis of the DyFe(2.33)Al(0.67) (or x=0.67) sample. The samples with x=1.1 and 1.2 were also analyzed, and each found to be a mixture of more than two phases. (C) 2010 International Centre for Diffraction Data. [DOI: 10.1154/1.3507088]
关键词:
X-ray powder diffraction;DyFe(3-x)Al(x) system;structure change;anomalous phase composition;magnetic-properties;intermetallic compounds;al substitution;rare-earth;fe;dy6fe23;refinement;aluminum;dy2fe17;co
朱桂兰
,
何崇智
钢铁研究学报
简要介绍了德国布鲁克AXS公司新产品D8系列X射线衍射仪的特点、实验方法的分析软件及其应用.该系列仪器具有超前的技术,卓越的品质,可为物质微观结构的分析和前沿研究工作提供有效的解决方案.
关键词:
X射线衍射仪
