Q.B. Yang
,
G.J Shifietand E.A. Starke
,
Jr(Department of Physics
,
Xiangtan University
,
Xiangtan 411105
,
China)(Depedment of Materials Science and Engineering
,
University of Virginia
,
Charlottesvil1e
,
VA22903
,
USA)
金属学报(英文版)
A clear understanding of the structure of the S precipitates which are present in Al-Li-X alloys is verp imporiant because the S -phase decreases the localization of strainand promotes less anisotropic properties during deformation. The close structural re-lationship between the S-phase and the Al matrix and their possible intedece bound-ary strvcture are described in detail. The proposed model is in good agreement with::::rimental obserwations. The dynamics Of the phase trunWrmation and possiblermation mechani8ms for the S,-phase are alSo proposed.
关键词:
Al-Li alloy
,
null
,
null
吴爽爽
,
莫兴婵
,
韦成峰
,
韦小圆
,
朱文凤
,
覃远东
,
刘来君
材料导报
采用传统的固相反应法制备了Cu欠量的CaCu3 Ti4 O12 (CaCu2.7Ti4 O12)陶瓷,研究了不同烧结时间对CaCu2.7Ti4O12相结构、显微形貌、介电性能和J-E非线性特征的影响.结果表明,延长保温时间降低了CaCu2.7-Ti4 O12陶瓷的中低频介电损耗和击穿场强并且显著提高了其介电常数.采用肖特基热电子发射模型对其非线性特征和电学性能的变化机理进行了分析,认为耗尽层宽度是影响电学性能的主要因素.保温30 h的CaCu2.7Ti4 O12陶瓷有望作为低压压敏电阻应用于半导体电路中.
关键词:
CCTO陶瓷
,
电流-电压非线性
,
压敏电阻器
,
巨介电响应
臧超飞
,
何豫生
,
沈庆飞
,
昌俊
,
李春光
,
张国华
,
罗胜
,
齐志
,
尹道乐
,
丁克俭
低温物理学报
doi:10.3969/j.issn.1000-3258.2001.04.008
我们应用脉冲电流的方法测量了Bi2Sr2CaCu2O8单晶在4特斯拉强场下的大电流时等温E-J特性.我们观察到在大电流时,样品电阻率ρ迅速增大,随着电流的继续上升,经过一段正曲率增长阶段,几乎达到饱和值,最后经过一段负曲率上升,达到正常态,显示出完整的S形.应用尹道乐等人的统一物质方程理论,给出了实验曲线较好的数值拟合.根据拟合结果,讨论了理论中各个参量的物理意义.
关键词:
崔岩
,
鲁二敬
,
吴晓明
,
张艳辉
,
吴昊
机械工程材料
通过拉伸、冲击、弯曲、硬度和金相等试验对S355J2G3低合金钢MAG焊焊接接头的力学性能与显微组织进行了研究。结果表明：采用G383G3Sil焊丝对S355J2G3低合金钢进行焊接时，可获得拉伸、弯曲和冲击性能均良好的焊接接头；接头硬度的分布较均匀，最高不大于380HV；焊缝组织为沿柱状晶晶界析出的块状先共析铁素体，晶内为细小密集的针状铁素体和少量珠光体；热影响区组织主要为先共析铁素体、针状铁素体、珠光体和少量的粒状贝氏体；母材为均匀细小分布的铁素体和珠光体。
关键词:
S355J2G3低合金钢
,
焊接接头
,
力学性能
,
显微组织
Physical Review B
The Hamiltonian for a four-sublattice Heisenberg ferrimagnet or ferromagnet with different exchange constants (J(ab) = J(cd) not equal J(bc) = J(da)) was established. An extended Bogoliubov transformation was developed by solving an equation group, consisting of 20 equations and 20 unknowns. The procedure for solving the equation group was carried out by introducing a simple way of reducing the numbers of the equations and the unknowns. The spin-wave spectra in the present system have been determined by performing the standard Holstein-Primakoff transformation and the Bogoliubov one. It has been found that the spin-wave spectra of the present system depend on the exchange constants and that the degeneracy of the spin-wave spectra remains. The results for a special case (J(ab) = J(bc)) i.e., an antiferromagnet are discussed briefly. The spin-wave spectra of the four-sublattice Heisenberg antiferromagnet are found to be degenerative also and they are linear in k for small k.
关键词:
model
Optical Materials
The perturbation formulas of the EPR g factors g,, g and g. for a 4f(11) 1 ion in orthorhombic symmetry are established. In these formulas, the contributions to the g factors arising from the second-order perturbation terms and the admixture of various states are taken into account. The above formulas are applied to the orthorhombic Er3+ centers in YAG, YGG and LuGG garnets. By analyzing their g factors, we find that the polar angles theta(j)(') of the impurity-ligand bonds related to the Z axis of the crystals in these Er3+ centers are smaller than the host angles theta(j) in pure crystals, whereas the azimuthal angles, related to the X axis in the impurity centers are larger than the corresponding phi(j) in the hosts. The g factors and their anisotropies Delta g [= g(z) - (g(x) + g(y))/2] and delta g (= g(x) - g(y)) for Er3+ in the garnets based on the above local structural parameters are in good agreement with the observed values. In addition, the angular distortions Delta theta (= theta(j)(') - theta(j)) or Delta phi (= phi(j)(') - phi(j)) obtained by analyzing the EPR data in this work are different from Delta theta(2), or Delta phi(2) (for only the second set of ligands, i.e., j = 2) based on the superposition model crystal-field analysis in the previous work. The validity of the results is discussed. (c) 2004 Elsevier B.V. All rights reserved.
关键词:
electron paramagnetic resonance (EPR);defect structure;crystal-field;and spin hamiltonians;Er3+;garnets
薛旭斌
,
王青云
,
范会卿
材料开发与应用
选取大理石作为研究对象,对大理石粉料进行了筛分并进行了焊条制备和测试.研究了药皮原料中大理石的颗粒度对E5015焊条熔敷金属化学成分及力学性能的影响.试验结果表明:随着大理石颗粒度的减小(由40-60目减小至100目以下),E5015焊条的熔敷金属化学成分Si、Mn含量逐渐下降,其熔敷金属屈服及抗拉强度逐渐降低而冲击功则逐渐升高.
关键词:
焊条
,
大理石
,
颗粒度
,
力学性能
Communications in Theoretical Physics
By using the wavefunctions obtained from diagonalizing the complete d(3) energy matrix at normal and various pressures, the g factor of the ground state of SrTiO3:Cr3+ and its pressure-induced shift have been microscopically calculated. Only by taking the local strains around Cr3+ in SrTiO3:Cr3+ (which are about twice the bulk ones) and corresponding P-chi dependence, can we obtain a good agreement between the calculated result of pressure-induced shift of ground-state g factor and the experimental one. The physical origins of this pressure-induced shift have been explained. It is found that the change of Dq(-1) with pressure makes main contribution to the pressure-induced shift of ground-state g factor of SrTiO3:Cr3+. By using the wavefunctions obtained from diagonalizing the complete d3 energy matrix at normal pressure, the relevant matrix elements and accordingly strain-induced splittings of t(2)(3) E-2 and t(2)(3) (4)A(2) of SrTiO3:Cr3+ have been calculated. The important results of Y-c, Z(c), P-c and Q(c) have also been evaluated. It is the admixtures of basic wavefunctions resulted from the spin-orbit interaction and/or Coulomb interaction and/or Kramers degeneracy that make the strain-induced splittings of the levels nonzero. It is found that there are nonvanishing matrix elements of operators T2 xi, T2 eta and T2 zeta between wavefunctions with positive M-s and those with negative M-s', which have important effects on the strain-induced splittings of the levels.
关键词:
crystal fields;energy spectrum;g factors;high-pressure effect;strain-induced splitting;theoretical calculations;ruby;crystal
