Journal of Applied Physics
Based on the developed multiple-scattering theory [C.-W. Nan and F. S. Jin, Phys. Rev. B 48, 8578 (1993)], an effective-medium theory (EMT) is proposed to treat coupled electromechanical behavior in composite media. The explicit relations for determining effective behavior of piezoelectric composites are derived. To illustrate the technique, numerical results of piezoelectric ceramic/epoxy composites for various particle shapes are presented over the whole range of concentrations. The EMT estimates are shown to be in good agreement with available experimental results. Porous piezoelectric ceramics are also discussed. The EMT predicts a similar critical behavior for heterogeneous piezoelectric materials to recent experiments.
关键词:
electromechanical properties;ceramics
李玉伟
,
陈继红
,
唐东明
,
张豹山
,
鹿牧
,
陆怀先
功能材料与器件学报
doi:10.3969/j.issn.1007-4252.2010.02.011
制备了一系列具有铁磁/反铁磁交换偏置作用的[NiO/Fe65Co35]10多层膜,使用振动样品磁强计(VSM)测量了样品的静磁参数,利用微带线法测量了样品4GHz-10GHz的磁谱,首次制备并测得了自然共振频率(fr)在6GHz以上,最高到f=9.6GHz的薄膜样品.结果表明交换偏置场(Hex)、各向异性场(Hua)、以及矫顽力(Hc)随铁磁层厚度(tFM)增大而减小;基于Landau-Lifishitz (L-L)方程对静磁参量和磁谱进行了比较,发现样品自然共振频率较L-L方程计算值偏大30%以上.
关键词:
铁磁
,
反铁磁
,
交换偏置场
,
各向异性场
,
交换耦合能密度
,
自然共振频率
Acta Materialia
In a first report [Jin ZH.. Gumbsch P, Ma E, Albe K, Lu K, Hahn H, et al. Scripta Mater 2006;54:1163], interactions between screw dislocation and coherent twin boundary (CTB) were studied via molecular dynamics simulations for three face-centered cubic (fcc) metals, Cu, Ni and Al. To complement those preliminary results, purely stress-driven interactions between 60 degrees non-screw lattice dislocation and CTB are considered in this paper. Depending on the material and the applied strain, slip has been observed to interact with the boundary in different ways. If a 60 degrees dislocation is forced by an external stress into a CTB, it dissociates into different partial dislocations gliding into the twin as well as along the twin boundary. A sessile dislocation lock may be generated at the CTB if the transited slip is incomplete. The details of the interaction are controlled by the material-dependent energy barriers for the formation of Shockley partial dislocations from the site where the lattice dislocation impinges upon the boundary. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
关键词:
dislocation;slip;twinning;twin grain boundary;molecular dynamics;molecular-dynamics simulation;grain-boundaries;nanocrystalline;materials;cross-slip;rate sensitivity;deformation;copper;strength;aluminum;fcc
曹春海
,
杨名
,
张世远
,
杨森祖
,
崔旭高
,
尤立星
,
吉争鸣
,
康琳
,
许伟伟
低温物理学报
doi:10.3969/j.issn.1000-3258.2003.03.002
采用Nd0.7Sr0.3MnO3/SrTiO3/YBa2Cu3O7-δ的异质结构,研究了自旋极化准粒子的注入效应.在56μm宽的YBCO膜条上成功地制备了与超导膜条同样宽度但不同长度的六个注入结区,长度L分别为80μm, 40μm, 20μm, 10μm, 5μm和2μm.80nm厚的YBCO薄膜在16K温度下Jc为2×105A/cm2.Iin=0.5mA的自旋电流注入下,随L从80μm逐渐顺次减小时,注入效率η=ΔJc/ΔJin逐渐增大.而当L≤20μm后,η不再增加,达到几乎相同的值(～6).初步分析认为这与自旋极化准粒子在超导膜内的有效自旋扩散长度有关.异质结构中YBCO薄膜的超导电性以及注入窗口的尺寸对获得大的自旋注入效率十分重要.
关键词:
注入效率
,
自旋准粒子
,
巨磁阻
,
异质材料
