NEUTRON SCATTERING AND LATTICE DYNAMICAL STUDIES OF THE HIGH-PRESSURE PHASE ICE (II)

Lattice dynamical calculations have been carried out for ice II based on the force field constructed for ice Ih. In order to fully understand ice II inelastic neutron scattering spectra, the decomposed phonon density of states was shown mode by mode. Calculated results have shown that the hydrogen bond force constant between the six-molecule rings is significantly weaker, 75eV/nm², compared with the force constant, 220eV/nm², within the rings. Inelastic neutron scattering spectra of clathrate hydrate H₂O+He are almost the same as ice II. This means that the absorption of He atoms cannot affect the bond strengths of the ice II host lattice. Based on the force field model for ice II, the van der Waals interactions between water molecules and helium atoms are considered. The results obtained are consistent with experimental data. Lattice dynamical calculations have been carried out for ice II using seven rigid pairwise potentials. It was found that MCY makes the stretching and bending interactions in ice II too weak and makes the O-O bond length too long (～5%), thus its lattice densities are obviously lower than other potential lattices or experimental values.     

Phonon density of states of tetracyanoethylene from coherent inelastic neutron scattering at Dhruva reactor

Inelastic neutron scattering experiments to determine phonon density of states of coherent scattering samples of polycrystalline complex solids are generally intensity-limited and therefore are feasible only at high flux facilities. Phonon density of states of the monoclinic phase of tetracyanoethylene at 300 K, obtained using the medium resolution triple axis spectrometer at the new Indian medium flux reactor Dhruva are reported here. The raw data is converted to the “neutron weighted” phonon density of states by applying suitable corrections. Comparison made with results from a theoretical calculation based on a semirigid molecule model of lattice dynamics is fair. Results from Dhruva are also consistent with that obtained (to be published) at the high flux pulsed neutron source (ISIS) of the Rutherford Appleton Laboratory in United Kingdom.     

四方相BaTiO_3及BaTiO_3∶Ce的拉曼散射特性研究

本文报道了在室温下ＢａＴｉＯ３及ＢａＴｉＯ３：Ｃｅ的拉曼谱的特点，着重讨论了前向散射配置下两个１Ｉ（ＴＯ）模（位于２７５ｃｍ－１和５１６ｃｍ－１左右）出现在Ａ１（ＴＯ）谱中的原因。通过设计特别的前向散射实验得到了此配置下由于晶体出射面对入射光的反射造成的背向散射的强度。在ＢａＴｉＯ３的前向散射谱中扣除了背向散射信号后，两个宽峰基本减掉，而掺Ｃｅ后经同样扣除背向散射信号两宽峰却依然很强。这样便证明了它们在前向散射中的出现与杂质有关系。在ＢａＴｉＯ３扣除背向散射后的谱中，还首次观察到一个位于４９２ｃｍ－１的峰。掺Ｃｅ后晶体的吸收曲线有很大变化，本文还讨论了吸收对散射强度的影响。     

稀土配合物的喇曼散射和超喇曼散射效应

以可见光为激发光,观测了稀土配合物的喇曼散射和超瑞利、超喇曼散射光谱,简单论述了超瑞利和超喇曼散射的理论,对实验测出的谱线进行了认证与分析     

钙钛矿(CaTiO_3)高压相变及等温压缩

高温高压条件下对钙钛矿(Perovstsite)多晶进行了研究,在金刚石压砧设备上压力条件最高达38GPa,YAG莱塞加热温度近1000℃以上,用红宝石萤光校压系统进行压力标定。实验结果表明静水压条件X射线就位测量,CaTiO_3(Ⅰ)由斜方晶系在10GPa时直接向六方CaTiO_3(Ⅱ)结构相变,体积变化为1.6％;1000℃加热及非静水压条件下,CaTiO_3(Ⅰ)由斜方晶系首先转变为四方晶系CaTiO_3(Ⅲ)转变压力为8.5GPa,体积变化0％,继续增加压力到15GPa,CaTiO_1(Ⅲ)向CaTiO_3(Ⅱ)转化成六方晶系,体积变化亦为1.6％。三种高压相,在压力降到一个大气压时都会消失,所以是逆转化的非淬火相。 等温压缩在标准静水压条件下进行,压力应小于10.4GPa,K_0~'=5.6时,X_o=210±7GPa,此数据是根据Birch-Murnaghan状态方程求得的体模重。     

Proton dynamics in hydrogen-bonded systems

The proton mean kinetic energy Ke(H) in various systems was calculated between 5 and 320 K using a semi-empirical (SE) approach. The SE calculation relies on the harmonic approximation and decoupling between the various modes, where the input data of the internal and external frequencies were taken from inelastic neutron scattering (INS) and IR/Raman experiments. The studied systems included ordinary H₂O phases, water of crystallisation in sulphate salts, adsorbed water and water confined in various samples of pore dimensions less than 20 Å. These included some zeolites, periodic mesoporous organosilicas (PMOs), beryl, Bikitaite and single- and double-wall carbon nanotubes. All SE calculated Ke(H) values were close to that of pure ice/liquid water, for which a good agreement was found with the deep inelastic neutron scattering (DINS) measurements. However, for water in Beryl at 5 K and ice in carbon nanotubes, at 170 K, large deviations from DINS results were found. Some insight into this problem may be gained by comparing those deviations with recently studied anharmonic systems involving proton double well potentials: Rb₃H(SO₄)₂ and KH₂PO₄, where an excellent agreement was obtained between SE calculations and DINS measurements.     

金属低温杂质散射电阻率

用弛豫时间近似讨论了金属低温下杂质散射电阻率与温度的关系，给出了近自由电子系统的电阻率的温度平方项系数。并对其它情况进行了讨论。     

Investigations of Solid State Dynamics at the NRSSR Beamline at PETRA II. An Overview

The present status of the new nuclear resonance beamline PETRA 1 at HASYLAB, DESY, Hamburg is described. Besides an overview of the experimental setup some examples of recent experiments are given. Those cover the main applications, i.e., inelastic scattering from iron alloys and quasielastic scattering from glass-forming liquids. This revised version was published online in August 2006 with corrections to the Cover Date.     

散射相函数对一维介质内辐射传递的影响规律

采用有限体积法研究了一维线性各向异性散射介质内散射相函数对辐射传递的影响规律.经与理论解、辐射元法、蒙特卡洛法计算结果比较表明,有限体积法的计算结果更可靠,且不同散射相函数的辐射换热系统中,其无因次热流之比与光学厚度之间存在某种单调变化的函数关系,利用该函数关系可以检验模型的准确度.     

受激布里渊散射相位共轭现象的二维数值模拟

 使用P.H.Hu等人[3，4]提出的计算途径，数值解了A.Flusberg等人[2]提出的零级方程。计算了布里渊池内随位置而变化的斯托克斯光强度、泵浦光强度和保真度，得到了布里渊池内几个位置上的斯托克斯光相位和强度的横向分布，并计算了泵浦光入口处的反射率和保真度。     

卢瑟福散射与原子的有核模型

回顾了卢瑟福散射实验,并从原子的有核模型的建立引出一些思考。     

高压下顽火辉石的相态用其地球物理意义

利用Birch-Murnahan有限应变状态方程和Gru neisen　状态方程,计算了钙钛矿型((Mgo. 86Fe     

单晶硅薄膜面向热导率分子动力学研究

采用非平衡分子动力学方法(NEMD)研究了室温(300 K)下厚度为2～32 nm的单晶硅薄膜的沿膜平面方向的热导率,并使用Debye-Einstein模型对模拟温度进行了量子修正。模拟表明薄膜面向热导率小于相应的大体积值,并随膜厚度减小而减小,具有显著的尺寸效应。在模拟范围内膜面向热导率略大于其法向热导率;与声子气动力论的定性结果一致。晶体的表面弛豫和表面重构现象导致了MD模拟中体系总内能的升高。     

带电粒子在四电荷点阵中的运动

本文讨论了带电粒子在四电荷点阵平面中所受的作用力以及不同初始条件下的运动。     

电子回旋激射不稳定性与磁化中子星的线发射

结合典型的磁化中子星HerX-1的硬X谱线,对相对论情形的电子回旋激射不稳定性作了进一步研究。计算了FX模的频率随传播方向的变化,FX模的增长率随波矢k的变化,中子星的引力和非热电子的平均动能对不稳定性增长率的影响,并对所得结果作了分析讨论。     

金刚石和石墨之间相转变几率的研究

 以势垒渡越模型为基础，对石墨和金刚石的相转变几率在压强-温度（p-T）图上的分布进行了研究。从理论上得到了金刚石和石墨的亚稳态相区边界，理论计算得到的相转变几率分布与文献报道的相转变速率的实验结果具有相同的规律。高温高压法合成金刚石的p-T特征程序可以用相转变几率的分布来解释。     

双层介电系统的Raman散射——ZnSe/玻璃和ZnSe/GaAs的表面声子模

本文实验观测了双层介电系统ZnSe/玻璃和ZnSe/GaAs的表面声子模,并利用极化场边界条件对上述体系的表面声子频率进行了计算。实验结果与计算结果符合得比较满意。     

O_2－Ag（111）表面散射经典轨道研究

利用分子动力学方法，采用三体简化模型及刚性转子近似，模拟计算了同核双原子分子Ｏ２小角度入射Ａｇ（１１１）表面，分子碰撞诱导解离几率，结果与实验规律一致。同时也获得了入射分子取向效应及散射分子的角分布对碰撞能的依赖关系等动力学信息。     

能态密度及其在解释半导体物理问题中的应用

通过对半导体杂质饱和电离，灰锡半导体特性以及Ｇｕｎｎ效应等的解释，指出能态密度在研究半导体物理现象中的重要应用。     

二维晶格中激波的传播和自由面反射的分子动力学数值研究

本文用分子动力学方法研究和计算了面心晶体中沿(1、0、0)面或休心晶体中沿(1、1、0)面上激波的传播和自由面反射现象。在所研完的范围内(u_p=10~75×10⁴cm/sec)粒子速度沿平均值的振动是不衰减的,激皮的传播速度和波后粒子速度的平均值呈线性关系。激波在自由面反射后,自由表面附近的粒子速度为活塞速度的二倍,这和宏观力学结果相同。此外,还出现最外层分子不断地以更高的速度被抛离的现象,这和宏观测量的微物质喷射现象亦类似。在稍后的阶段,还显示出内部粒子间被拉开的"微断裂"现象。