High-pressure Mössbauer spectroscopy with nuclear forward scattering of synchrotron radiation

Abstract

Using a diamond anvil cell, high-pressure ⁵⁷Fe Mössbauer spectroscopy has been performed with the nuclear forward scattering of synchrotron radiation. A pressure-induced magnetic hyperfine interaction at ⁵⁷Fe in SrFeO_{2, 97} has been detected at 44 GPa and 300 K for a first time by a quantum-beat modulation of the decay rate after collective nuclear excitation by the synchrotron pulse. The basic concept and method used to detect nuclear forward scattering with synchrotron radiation are discussed.     

块体非晶合金Zr55Cu30Al10Ni5 结构弛豫的研究

应用同步辐射小角x射线散射和差示扫描量热分析对块体非晶合金Zr55₅₅Cu 30₃₀Al10₁₀Ni5₅结构弛豫进行了研究.实验结果表 明：经340℃、不同时间退火后的非晶内 部的电子密度涨落随退火时间的延长先增大而后减小；玻璃转变温度附近焓弛豫峰的表观激 活能则随退火时间的延长先减小而后增大.结果反映了随退火时间的延长，块体非晶合金内 部类液体区不断减少及类固体区不断增加的过程. 关键词： 小角x射线散射 块体非晶合金 结构弛豫     

小角X射线散射方法测定二氧化硅干凝胶的平均孔径

提出了当多孔体系的小角X射线散射不遵守Porod定理的情况下,应用Debye法(相关函数法) 和Guinier法(逐级切线法和多级斜线法)计算它们的平均孔径的方法.对不同制备条件下部分 二氧化硅干凝胶的测试,取得了比较一致的结果,并与氮气吸附法测定结果进行了对比. 关键词： 小角X射线散射 二氧化硅干凝胶 平均孔径     

The structure of the glass phase of Rb1−x(ND4)xD2PO4

X-ray scattering techniques have been used to study the diffuse scattering from a single crystal of Rb_1–x(ND₄)_xD₂PO₄ withx=0.65. This system has a structural glass phase at low temperatures resulting from the competing ferroelectric interactions of RbD₂PO₄ and antiferroelectric interactions of (ND₄)D₂PO₄. The diffuse scattering shows a broad peak with a maximum occurring at a wavevector of about 0.3a ^*, and the intensity of these peaks is surprisingly different for wavevectorsq on opposite sides of the Bragg reflections. A model of the D bonding is developed which suggests that the diffuse scattering arises from the interaction between ferroelectric displacements alongc, ferroelectric displacements alongb, and transverse acoustic modes polarized alongb andc. The model accounts for the incommensurate wavevector and, qualitatively, for the intensity of the diffuse scattering around different Bragg reflections. The temperature dependence of the scattering is also measured.     

用原位x射线小角散射研究块体非晶合金Zr55Cu30Al10 Ni5的结构弛豫

应用同步辐射x射线小角散射法在原位对块体非晶合金Zr₅₅Cu₃₀Al ₁₀Ni₅在等温退火过程中的微结构变化进行研究.实验表明：在等温退火过程中电子 密度涨落反映了晶化之前的结构弛豫过程；在一定的退火温度下、随退火时间的增加，拓扑短程序弛豫与化学短程序弛豫之间存在一个电子密度均匀化的过程；导致这两种弛豫过程转变的退火时间与退火温度有关，温度越高，所需的退火时间越短. 关键词： 原位x射线小角散射 块体非晶合金 等温退火 结构弛豫     

Time-domain interferometry using synchrotron radiation applied to diffusion in ordered alloys

Time-domain interferometry of synchrotron radiation (TDI) has recently been used as a tool for investigating diffusion in glasses. This work deals with an extension of this technique to ordered structures. In a TDI experiment performed on the B2 alloy CoGa at the APS the intensity scattered into Bragg directions showed no detectable quasielastic signal. Experimental lower limits of the elastic contribution are given. They are in accordance with the coherent scattering function derived in this paper. This result indicates that TDI can be applied to diffusion in crystalline solids, e.g. intermetallic alloys, by using diffuse scattering. Requirements and limitations of diffuse scattering experiments are discussed. Received 21 September 2000 and Received in final form 13 December 2000     

非晶态合金Fe83B17和Ni64B36结构的研究

本文叙述了用偏振中子衍射方法对Fe₈₃B₁₇非晶合金和中子衍射方法对Ni₆₄B₃₆非晶合金的结构研究。由实验数据计算了每种合金的偏干涉函数(PSF)S_ij(Q),和偏简约径向分布函数G_ij(r)。并得到原子短程结构上的各项参数。在此基础上,讨论了这一类非晶态合金的结构模型,计算了其一种模型简单单元的中子衍射散射强度,并和实验所得的结果作了比较。 关键词：     

Mössbauer studies of the layered compound 1T-TAS2

We report the temperature dependence in Tantalum Disulfide 1T-TaS₂ of the elastic and inelastic intensities of the first order satellite (1.285, 0, 0.333) and (3, 0, 0.21) near the Bragg peaks (1, 0, 0) and (3, 0, 0), respectively. The phason temperature factor has been measured as a function of temperature from 70 to 295 K using Mössbauer gamma-ray scattering. The high-energy resolution provided by this technique allowed experimental separation of the elastic scattering from the inelastic thermal diffuse scattering. The first order satellite is found to be 15% inelastic. The results were compared with those found by Chapman and Colella obtained by X-ray method (Moret and Colella, Phys. Rev. Lett. 52:652, 1984).     

Electric-field influence on the neutron diffuse scattering near the ferroelectric transition of Sr0.61Ba0.39Nb2O6

ABSTRACT

Uniaxial relaxor ferroelectric Sr_0.61Ba_0.39Nb₂O₆ single crystal has been investigated in the vicinity of its phase transition using neutron scattering and dielectric spectroscopy. A global-type thermal hysteresis is evidenced by both techniques in the ferroelectric phase and up to about 15 K above T_c. In addition, a part of the transverse neutron diffuse scattering in the 001 Brillouin zone, presumably related to static nanodomain structure, can be suppressed by prior poling the crystal in electric field of 3 kV/cm. The remaining part of the transverse neutron diffuse scattering and the real part of permittivity show a similar temperature dependence. The temperature position of the maximal scattering intensity T_max depends significantly on the scattering wave vector. T_max shifts monotonically to higher temperature with the increasing wave vector in all investigated cooling and heating regimes. It is concluded that the critical fluctuations have space correlations which depend on frequency and wave vector.     

Orthorhombic to tetragonal phase transition in high TC superconductor YBa2Cu3O7-y and NdBa2Cu3O7-z under high pressure

Abstract

X-ray powder diffraction measurements for YBa₂Cu₃O_7-y and NdBa₂Cu₃O_7-y were made at the intense synchrotron radiation source under high pressure up to 5 GPa. These samples were wrapped tightly in platinum foil to avoid deoxidizing atmosphere. The orthorhombic to tetragonal transition temperature increases with pressure in both samples. These results are discussed on the basis of the disordering of the oxygen atoms on the chain sites.     

Structure Formation from the Oriented Glassy States of Poly(Ethylene Terephthalate)

The ordering process of poly(ethylene terephthalate) (PET) from the oriented glassy states during the isothermal annealing process was investigated using real-time X-ray scattering experiments with synchrotron radiation sources. The X-ray scattering intensity of the 001' reflection, which is a measure of the smectic order with respect to chain alignment, increases with time and then begins to decrease after reaching a maximum. The intensity of the four-point pattern in the small-angle X-ray scattering region, which is a measure of the fraction of a crystal-like structure with a tilted lamellar structure, increases monotonically with time. Hence, the fraction of PET chains with smectic-like order has a maximum during the isothermal process, while that of the crystal-like structure increases monotonically. The kinetics of structure formation from the nematic-like structure to the crystal-like structure by way of the smectic structure will be discussed.     

Investigation of craze development using small-angle X-ray scattering of synchrotron radiation

The development of crazes in polycarbonate was investigated with the method of ultra-small-angle X-ray scattering (USAXS) of synchrotron radiation. Measurements at different temperatures and with different draw rates were carried out. The two-dimensional scattering patterns were analyzed by means of a fibrillar model of the craze. The geometrical parameters of the craze as a function of the macroscopic draw ratio were determined by using a curve-fitting procedure. From the measured values of the diameter and the mean distance of the fibrils, it is possible to calculate the volume fraction v_f of the fibrils directly. Additional scattering caused by submicrocracks is discussed.     

Temperature variation of the Debye-Waller factors of metal and halide ions in CsCl and CsBr powders by X-ray diffraction. II. Debye-Waller factors of Cs+ and Br− ions in CsBr from room temperature to 78.2°K

The temperature variation of the Debye-Waller factors of Cs⁺ and Br⁻ ions in CsBr powder has been studied using powder X-ray diffraction. The integrated intensities of the Bragg peaks at different temperatures have been obtained. These results have been verified by structure factor least squares refinement program. Theoretical shell model lattice dynamical calculations have been done using a 7-parameter model in the harmonic approximation and the values compared with the present X-ray measurements. The observed intensities have been corrected for first order thermal diffuse scattering.     

Angular Dependence of L X-ray Relative Intensities of Uranium and Thorium at 59.5 keV

INTRODUCTION

The knowledge of relative intensities of K, L and higher shell X-rays is needed for the investigation of various phenomena in atomic physics. In earlier studies, L X-ray relative intensities and energies have been reported for many elements by several investigators [1–5], but the angular dependence of L X-ray relative intensity has not been reported. According to Flugge et a1 [6], if the angular momentum J=1/2 and J>1/2 of the originating shell, then the angular distribution of X-rays is isotropic and anisotropic, respectively. From this idea, L_α, L_l and some of L_β, intensities are dependent on changing the scattering angles. In this study, we have measured the angular dependence of L_α, La_l, L_α/L_β, and L_α/L_γ, intensity ratios of U and Th at different angles varying from 45° to 135°.     

Crystal structure of NaNO3 at high pressure

Abstract

Effect of high pressure on the crystal structure of rhombohedral NaNO₃ was investigated by X-ray diffraction of single crystals mounted in a miniature diamond-anvil cell on synchrotron radiation source. Diffraction intensity measurements were made at three pressures across a suggested transition pressure 4.3 GPa. No change was observed in an overall distribution of reflections in the reciprocal space with increasing pressure, but there was a systematic variation in diffraction intensity for particular groups of reflections. An analysis based on the structure factor calculation showed that a structure change induced by pressure is mainly a rotation of the nitrate groups in the alternate layers along the threefold axis in opposite directions. Least-squares refinement of the atomic positional parameters yielded the angle of the rotation to be 4.3 and 7.0 deg at pressures of 4.4 and 5.0 GPa, respectively. It has also been shown that the positions of the sodium and nitrogen atoms are slightly displaced along the axis, resulting in the formation of dipoles in the high pressure phase.     

X-ray magnetic scattering

The magnetic scattering of synchrotron X-rays has been developed to the point where it is now a standard technique for the study of magnetism and magnetic materials, often complementing neutron investigations of magnetic structures. In this article, after a brief historical introduction, examples of experiments on lanthanide and actinide antiferromagnets are presented. X-ray diffraction and Compton scattering studies of ferromagnets are then considered. Finally future prospects and possibilities are discussed.     

Cu-Ni alloy nanocluster formation by ion implantation in silicate glasses: Structure and optical properties

Sequential ion implantation (copper and nickel) in silica and soda-lime glasses has been performed. The formation of copper-nickel alloy nanocluster in the glass host has been evidenced by synchrotron radiation-based techniques, namely X-ray diffraction and absorption spectroscopy. The nanocrystals' lattice parameter value was estimated, indicating the formation of Cu₅₅Ni₄₅ alloy particles. Optical absorption spectra are also discussed. Received 6 May 1999 and Received in final form 22 September 1999     

Tin–DNA complexes investigated by nuclear inelastic scattering of synchrotron radiation

Nuclear inelastic scattering (NIS) of synchrotron radiation has been used to investigate the dynamics of tin ions chelated by DNA. Theoretical NIS spectra have been simulated with the help of density functional theory (DFT) calculations using 12 models for different binding sites of the tin ion in (CH₃)Sn(DNA_Phosphate)₂. The simulated spectra are compared with the measured spectrum of the tin–DNA complex.     

铁磁形状记忆合金Mn2NiGa中应力诱发马氏体相的结构和磁性

采用金刚石对顶砧高压装置（DAC）和同步辐射X射线光源法,对Heusler类型的磁性形状记忆合金Mn₂NiGa的结构进行了原位高压X射线衍射测量,并对卸载后的受压样品进行了磁测量.实验观察到材料在室温下分别在0.77 GPa和20 GPa压力下发生了两次不可逆结构相变：马氏体相变和两种不同马氏体间的等结构相变.同时加压使马氏体结构中产生了大量的缺陷,造成了严重的晶格畸变,致使马氏体结构的矫顽力提高了近10倍,达到204 kA/m.结果发现,加压处理造成样品马氏体相饱和磁化强度的大幅度 关键词： 铁磁形状记忆合金 2NiGa')" href="#">Mn₂NiGa 高压 同步辐射     

Diffuse X-ray scattering near a two-dimensional liquid–vapor phase transition at the <Emphasis Type="Italic">n</Emphasis>-hexane–water interface

The molecular structure of neutral n-triacontanol mesophases at the n-hexane–water interface has been studied by diffuse X-ray scattering using synchrotron radiation. According to the experimental data, a transition to the multilayer adsorption of alkanol occurs at a temperature below the transition from a gas phase to a liquid Gibbs monolayer.