Journal of Physics-Condensed Matter
In this paper, we carry out a detailed theoretical investigation of the temperature dependence of zero-field splitting (characterized by Delta D(T) = D(T) - D(0)) of Al2O3:Fe3+ crystals by taking into account both the static contributions due to the thermal expansion of crystal and the vibrational contributions due to the electron-phonon interaction. The static contributions are calculated from the spin-orbit coupling mechanism, the relativistic mechanism, the covalency and overlap mechanism and the spin-spin interaction mechanism. Similar to the studies on the specific heat of crystals, the vibrational contribution of phonons of acoustic branches is given using the long-wavelength approximation and that of phonons of optical branches is calculated using a single-frequency model. The calculated results show that the contribution coming from the coupling with optical phonons is comparable with that due to the thermal expansion and that, to reach good fits between the theoretical and experimental Delta D(T), all the contributions from the thermal expansion and the electron-phonon (including the optical and acoustic phonons) interaction should be taken into account.
关键词:
symmetry
董建敏
,
李华
,
张昌文
,
潘凤春
,
王永娟
,
甄鹏
金属学报
采用MS-Xα方法研究了Nin (n=2—6)原子簇的电子结构和原子磁矩, 发现团簇的几何对称性对原子磁矩和电子态密度的分布有重要影响. 具有Oh点群对称的八面体原子簇Ni6的3Eg轨道上存在很强的负交换耦合, 呈现反铁磁耦合趋势; 具有C3v点群对称的三边金字塔结构的原子簇Ni5位于塔顶点的Ni原子与基面上的Ni原子磁矩方向相反, 但大小不等, 呈现出亚铁磁交换耦合特征. 与金属Ni相比, 有些Ni原子团簇磁性增强, 有些团簇磁性减弱. 这一结果能够较好地解释铁磁超微颗粒呈现出的表面磁性异常现象.
关键词:
Nin原子团簇
,
symmetry
,
electronic structure
G.B.Hu and Q.B.Yang (Department of Physics
,
Xiangtan University
,
Xiangtan 411105
,
China)(Beijing Laboratory of Electron Microscopy
,
Center for Condensed Matter Physics
,
The Chinese Academy of Sciences
,
P. O. Box 2724
,
Beijing 100080
,
China)
金属学报(英文版)
Excellent results are obtained in structure analysis with jew phases of structure factors by the maximum-entropy method (MEM) for CaGaN PbCO3 and ReBe22 single crystals. The computation time and memory space are minimized by symmetry operations so that structure analysis by the MEM can be carried out with a personal computer.
关键词:
maximum entropy method
,
null
,
null
,
null
吴建宇
,
龙源
,
纪冲
,
高福银
,
宋克健
兵器材料科学与工程
为研究炸高对环形聚能射流侵彻特性的影响,采用LS-DYNA有限元程序及Lagrangian-Eulerian流固耦合算法,对截面对称的小口径环形聚能切割器在不同炸高条件下射流成形及侵彻靶板的物理过程进行数值模拟,重点讨论炸高对切口对称性及侵彻深度的影响.数值模拟结果表明:在侵彻过程的3个阶段,射流依次经历了头部射流垂直侵彻、杵体偏向内壁运动、杵体偏向外壁运动的形态变化;随炸高增大,射流和杵体的偏离越明显,切口越不对称,切口截面形状依次为“漏斗形”、“葫芦形”、“椭圆形”;基于工程实际运用,可选取射流发生二次断裂的位置作为最佳炸高.
关键词:
环形聚能射流
,
炸高
,
侵彻深度
,
对称性
白雪
,
周国香
,
郭美玲
,
李佳
人工晶体学报
在本征铁弹相变的软模理论的基础上,依据弹性本构关系和居里原理,给出了立方晶系晶体所有可能的自发应变的种类,研究了立方晶系晶体本征铁弹相变序参量的选取问题.以Th群和Oh群为例,阐明了不同类的序参量导致晶体对称性变化相同的的原因,提出了该情况下序参量选取的“就少不就多”的原则.得到了发生本征铁弹相变时所有可能的序参量及晶体的对称性的变化.
关键词:
本征铁弹相变
,
立方晶系
,
序参量
,
对称性
管晨雪
,
曹艳超
,
何小玲
,
周海涛
,
张昌龙
人工晶体学报
对水热法生长的两种不同结晶习性的 BSO晶体进行了腐蚀像的观察研究，得到了{100}、{110}、{211}、{111}晶面的腐蚀形貌特征，建立了BSO晶体腐蚀像在三维空间分布的立体模型。研究发现不同单形晶面的蚀坑形态不同，但都体现了晶体的对称性。不同晶面腐蚀难易程度与晶体结构有关。
关键词:
水热法
,
BSO
,
蚀像
,
对称
