Amorphization of ice near the melting point

In addition to reflections of the hexagonal phase of ice I _h, the intense diffuse scattering of X-rays mainly due to the amorphization of ice is revealed on the X-ray diffraction patterns of water ice samples prepared at liquid nitrogen (studied by the authors earlier) and samples prepared at T = ?10°C (this work). The measurements are performed in the temperature range from ?25 to 0°C. The existence of reflections of the crystalline phase and intense diffuse scattering on the X-ray diffraction patterns makes it possible make a conclusion about the coexistence of crystalline and amorphous structures of ice. Splitting of the first maximum on the electron-density radial distribution function is detected on the basis of an X-ray diffraction pattern recorded at T = ?3°C. This splitting is explained by an increase in the interatomic distances between the nearest-neighbor atoms located at different levels. Similar splitting was also detected on a radial distribution function constructed using an X-ray diffraction pattern recorded at ?10°C.     

Thermodynamics of magnetic alloys in the vicinity of the curie and melting point

The coincidence of two phase transitions of different order is discussed in the case of a liquid ferromagnetic alloy at constant pressure and zero field. Three phases at most are in equilibrium. The experimental data on the Au-Co alloy are briefly mentioned.     

Raman scattering from potassium iodide near the melting point

We have measured the Raman spectrum of potassium iodide in the crystalline phase at high temperatures, and in the melt. As temperature increases the various second order features in the low temperature spectra coalesce into a broad feature, which persists into the melt. A smooth, quasi-exponential wing also appears in the melt. Thus, the spectrum is structurally similar to those found in solid electrolytes and silver halide melts. Possible interpretations of the spectrum are indicated.     

Diffuse X-ray scattering in AuCu3

It has been shown that the intensity of diffuse X-ray scattering in a binary alloy monocrystal above the order- disorder temperature depends on the direction of the scattering vector with respect to the cristalline axes.     

Diffuse X-ray scattering in the metallic state of TSeF-TCNQ and HMTSeF-TCNQ

Some results of a X-ray diffuse scattering investigation on the charge transfer compounds TSeFTCNQ and HMTSeF-TCNQ are reported. In the metallic region the results show the formation of a 1-D distortion or a Kohn anomaly in the phonon spectrum. For TSeFTCNQ this is observed below T ～ 238 K and corresponds to a periodicity of (3.15 ± 0.05) |b| along the chain axis. For HMTSeFTCNQ the distortion was detected even at room temperature and has a period of (2.7 ± 0.1) |b|. In both materials the distortion has both transverse components in contrast to TTFTCNQ. In the insulating state of TSeF-TCNQ below 29 K the 1-D distortions on each stack are correlated to form a 3-D superlattice.     

Diffuse X-ray scattering from several platinum chain compounds

Values of the Fermi wavevector for several platinum based one-dimensional conductors were determined from diffuse X-ray scattering measurements. The values were compared with those expected from the chemical compositions. The importance of conclusive values of this parameter is stressed and the coupling between Peierls instability and other structural instabilities is discussed.     

On possibility of a structural transition in the vicinity of the melting point in liquid copper

The temperature dependence of the kinematic viscosity of liquid copper has been studied by the method of torsional vibrations during heating and cooling within the temperature range 1080–1500°C. A reversible structural transition was discovered in the vicinity of 1170°C. This transition manifests itself in a jumpwise change of viscosity and the activation energy of viscous flow at this temperature.     

Anisotropy of critical X-ray scattering in the vicinity of smectic B-nematic phase transition in EPPCB

The high-resolution X-ray scattering has been used to study the anisotropy of the density correlation function in the vicinity of S_B-N phase transition in the recently developed material EPPCB. The effective critical exponents estimated in the temperature interval 10^?4 <t< 10^?2 (t = T/T_C ? 1) are: γ = 1.34 ± 0.09, ν_⊥ = 0.56 ± 0.08, ν_| = 0.70 ± 0.06 and fulfill, within experimental errors, the relation γ = ν_⊥ + ν_|.The novel feature is that the iso-intensity contours in the scattering plane containing the direction normal to the smectic layers have been found to be of four-winged shaped. A phenomenological (mean-field) theoretical approach explaining this shape in terms of the independence of fluctuations in the longitudinal (perpendicular to the smectic layers) and transversal (in the smectic planes) directions has been proposed.     

Diffuse X-ray scattering and nanoclusters in the Hg2Br2 model ferroelastics

Diffuse maxima are revealed and studied for the first time in the x-ray scattering patterns of Hg₂Br₂ single crystals. These maxima originate from clusters of the orthorhombic phase due to the phase transition in the paraphase tetragonal matrix. The nucleation and growth of clusters are initiated by spatiotemporal fluctuations of the order parameter corresponding to the soft transverse acoustic mode at X points of the Brillouin zone boundary. Information on the behavior of the susceptibility and correlation length with variations in temperature and on the shape and anisotropy of the clusters is obtained, and the critical exponents are determined.     

Diffuse X-ray scattering from crystalline structures with quantum dots of pyramidal shape

Diffuse scattering from crystalline structures with quantum dots (QDs) in the shape of a regular truncated pyramid with a square base is investigated. The elastic strains around QDs are calculated using the Green function method. The fields of the QD atomic displacements and the angular distribution of scattering intensity in the reciprocal space as functions of the QD concentration are simulated numerically. The influence of a pyramidal QD cross section by the diffraction plane on the diffuse X-ray scattering is demonstrated.     

Diffuse x-ray scattering near Bragg peaks from point defects in a general lattice

Using the continuum theory of linear elasticity, diffuse x-ray scattering has been calculated in the immediate neighbourhood of Bragg peaks from point defects in a lattice containing more than one atom in the unit cell. General expressions are obtained for the Debye-Waller factor, Huang diffuse scattering and the asymmetric scattering due to the defect. For lattices with one atom per unit cell, these expressions reduce to the well-known formulae of diffuse scattering.     

Diffuse X-ray scattering from a calomel crystal near the temperature of the structural phase transition

X-ray scattering from a calomel crystal near the temperature of a structural phase transition is analyzed theoretically. It is shown that the diffuse lines of the x-ray diffraction, which correspond to both the X points and Z point of the Brillouin zone, are formed in the high-temperature phase. The latter lines result from the scattering by the beats of fluctuations of two components of the order parameter. Such lines were previously observed experimentally, but the nature of the lines corresponding to the Z point remained unclear. It is shown that the Z line at the point (5, 0, 0) should be an order of magnitude stronger than the observed Z line at the point (4, 3, 0).     

长柱状气溶胶粒子的光散射特性

以中纬度卷云中常见的长柱状冰晶为例,利用长柱状粒子光散射理论,探讨了入射光为线偏振时,电矢量平行和垂直于入射面情况下,单个长柱状粒子的散射光强度分布和偏振特性随入射角、尺度参数与偏振态的转化关系:随着入射角的增大,散射强度、偏振总体趋于对称且数值振荡频率降低,散射强度总体减小,偏振的改变程度总体增大;随着尺度参数的增大,散射强度、偏振的数值振荡频率增大,散射强度数值振荡峰的幅度整体减小,电矢量平行于粒子长轴时主偏振的数量、强度和位置皆有变迁,电矢量垂直于粒子长轴时前后主偏振位置相对固定;随着偏振度的减小,散射强度、偏振趋向于一致,两者的数值改变程度减小,当偏振度减小到0时,散射强度、偏振变得完全相同。选取火山尘埃和烟灰与冰晶对比,阐述了粒子散射光的强度分布和偏振特性随折射率的变化规律:折射率虚部不改变散射强度的整体趋势,但使散射强度和偏振的振荡峰幅度增大,当其数值较大时,使得偏振的数值振荡峰覆盖范围拓宽。     

Bubble-domain lattices in the vicinity of the compensation point

The behavior of a hexagonal lattice of bubble domains in thin uniaxial films of garnet ferrites is studied in the temperature range from the compensation point to the Néel temperature. Two types of first-order phase transitions (preserving and not preserving the total number of domains in the bubble-domain lattice) occurring with variation of the temperature were studied. It is shown that the type of a phase transition is determined by the temperature dependence of the characteristic length of the film. The existence of two types of phase transitions is explained in terms of magnetostatic pressure existing in a bubble-domain lattice.     

Scattering of sound by sound in the vicinity of the liquid-vapor critical point

We report an experimental study of the scattering of sound by sound in the vicinity of the liquid-vapor critical point of carbon dioxide. We measure the amplitude of the scattered difference frequency wave generated by acoustic bulk nonlinearities. We observe that it is strongly increased in the vicinity of the critical point.