The neutron diffraction study of liquid GeTe and As2Te3

The radial distribution analyses for GeTe and As₂Te₃ are made at temperatures above the melting point in the range of momentum transfer between 0.7 and 10.0 Å^?1 by the neutron diffraction technique. Furthermore, the local order in amorphous GeTe is determined by analyzing the intensity data of the electron diffraction of its thin film. The result for the amorphous film indicates that the local distribution of atoms in amorphous GeTe is not characteristic of the structure of its crystalline state. The shape of the peaks of the intensity curve for liquid GeTe differs from that for the amorphous and crystalline states. However, the short bond length and the small coordination number determined from liquid RDF suggest that the covalent-like bonding between nearest-neighbor atoms remains unbroken when melting. The general form of the structure factor for liquid As₂Te₃ is similar to that for the amorphous material reported previously. The position of the first peak of RDF in the liquid state is observed to be shifted to a shorter distance than the average of nearest-neighbor atoms in crystalline As₂Te₃. The structure of GeTe differs considerably between the crystalline, amorphous and liquid states, whereas the local order in the liquid As₂Te₃ is similar to that in the amorphous state but not in the crystalline state.     

The liquid state of large clusters with pairwise atomic interactions

Formation of the liquid state for clusters with a pair interaction between atoms is examined within the framework of the void model, in which configurational excitation of atoms results from formation of voids. Void parameters are found from computer simulation by molecular dynamics methods for Lennard-Jones clusters and from real thermodynamic parameters of the liquid states of condensed inert gases. Phase transitions are analyzed in terms of two aggregate states. This information allows us to divide the entropy jump during the solid-liquid phase transitions in two parts, so that one corresponds to configuration excitation at zero temperature, and the other is a contribution from thermal vibrations of atoms. The latter part contributes from approximately 40% for Lennard-Jones clusters consisting of 13 and 55 atoms up to 56% for bulk inert gases. These magnitudes explain the validity of melting criteria based on thermal motion of atoms, even though this phase transition results from configurational excitation of ensembles of bound atoms. It is shown that the void concept allows us to analyze various aspects of the liquid state of clusters including the existence of the freezing temperature below which no metastable liquid state exists, and the properties of glassy states which may exist below the freezing point.     

Electronic structure and properties of liquid caesium up to critical point by LMTO calculations

It is well-known that liquid caesium shows some unusual properties at low densities. We used supercell technique within linear muffin-tin orbital method to investigate this phenomenon. Electronic structure of liquid caesium for different temperatures from the melting point up to critical point was obtained. The atomic structure was simulated for a cluster of 2000 atoms by the Reatto method on the base of experimental structure factors of Cs obtained by Winter and co-workers for different temperatures (from 323 K up to 1923 K). The Kubo–Greenwood formula was applied for the calculations of melts conductivity. The received results indicate that metal–nonmetal transition in liquid cesium is connected not to the gap at Fermi energy in density of electronic states, but more likely with electrons localization on some kind of atomic clusters.     

铜、银及铂原子纳米团簇熔点随尺寸非单调变化的分子动力学模拟研究

采用分子动力学方法和原子嵌入法模型势模拟了铜原子、银原子及铂原子纳米团簇的熔化过程,研究了这些金属原子纳米团簇熔点与团簇尺寸的关系,发现各自在小于一定数目原子的金属纳米团簇的熔点不再随尺寸的变小而单调下降,通过对各种团簇溶化前后结构的比较研究,分析了导致这种现象的原因。     

The structure of liquid As2Se3 and GeSe2 by neutron diffraction

The liquid structures of As₂Se₃ and GeSe₂ have been investigated using the neutron diffraction patterns. In both cases the structure factor showed a low first peak maximum which follows a weak but apparent pre-peak at very low momentum transfer. It was also observed that the radial distribution function of both materials are characterized by the well-defined first neighbor shell because of the deep minimum on its right-hand side although in the liquid state. These results indicate that strong covalent bondings between unlike atoms in the solid state still remain when melting. Both the structure factor and the distribution curves of these alloys are, on the whole, similar to those in the amorphous phase which have already been examined. A slight difference in the coordination number, however, is found between amorphous and liquid phases of these materials.     

Viscous behaviour of undercooled metallic melts

Viscosity data for non-crystalline Au_0.77Ge_0.136Si_0.094 alloys in the region of the glass transition temperature and above the melting point, are fitted to a single expression of the type proposed by Doolittle. This expression also leads to reasonable values for the activation energy for hole formation in the liquid and for the liquid free volume at the glass transition temperature. A similar procedure was applied to the viscosity data of a Pd_0.775Cu_0.06Si_0.165 non-crystalline alloy. By assuming values for the liquid free volume at both the glass transition temperature and the melting point, the analysis is also extended to Pd_0.82Si_0.18 alloys for which no viscosity data are available. Here, time-temperature-transformation (T-T-T) curves for crystallization are calculated for each of the three alloys, and used to determine the critical cooling rates for the formation of an amorphous solid.     

Structural transformations in solid and liquid n-butanol from FTIR spectroscopy

Abstract

FTIR spectra of n-butanol were registered for temperatures from ?100 °С to 40 °С during heating of the sample and from 40 °С to ?170 °С during its cooling. Structural changes at phase transitions solid–liquid and liquid–solid were detected. At n-butanol cooling below the melting point the initial crystalline structure was not achieved. Instead of it, a super-cooled liquid or amorphous phase was obtained. Quantum-chemical simulation of 27 n-butanol rotational conformers were provided via ROCBS-QB3 method. According to the calculations, the most stable conformer is TG′t. Comparison of calculated in the anharmonic approximation IR spectra of possible monomers and dimers of n-butanol with experimentally registered spectra showed that there are no monomers and dimers in the studied sample, and the structure of n-butanol in the condensed state is formed by bigger clusters.     

Time resolved valence band photoelectron spectroscopy of liquid palladium and molybdenum

Photoelectron spectroscopy measurements on liquid transition metals are not feasible by conventional steady state experiments because of the elevated vapor pressures of these metals at the melting point. However, dynamic experiments with surface melting induced by pulsed laser irradiation combined with time resolved photoelectron spectroscopy make these experiments possible for the first time. Valence band spectra of Pd and Mo have been obtained by this method in both the high temperature solid phase and the liquid phase under identical experimental conditions. Both the elements reveal distinct changes in the valence band spectra on melting. The shapes of the 4d bands of the two metals in the liquid phase are in good agreement with the calculated spectra based on the ab initio density of states (DOS) calculations.     

Liquid properties of Pd-Ni alloys

Liquid properties of Pd-Ni metal alloys are computed by molecular dynamics (MD) simulation with the use of quantum Sutton-Chen potential (Q-SC) model. The thermodynamical, structural, and transport properties of the alloy are investigated. The melting temperatures for Pd-Ni system are predicted. The temperature and concentration dependence of diffusion coefficient and viscosity are reported. The transferability of the potential is tested by simulating the liquid state. The values of melting point are in excellent agreement with the experiment. Comparison of calculated structural and dynamical properties with the available experiments and other calculations shows satisfactory consistency.     

An apparent critical point in binary mixtures of m-nitrotoluene with n-alkanes; experimental and simulation study

We report a simulation study of the system m-nitrotoluene–n-decane, showing an apparent critical point, which lies in their metastable, experimentally inaccessible state, below their melting point, affecting physical and chemical properties of this systems in the stable liquid phase. The presence of the apparent critical point in this mixture has been experimentally observed by the non-linear dielectric effect (NDE) as an anomalous increase in the NDE values typical of critical concentrations. The phase diagrams of this mixture have evidenced that the system freezes in the homogenous phase and its melting point is higher than its critical temperature [M. Śliwińska-Bartkowiak, B. Szurkowski, T. Hilczer, Chem. Phys. Lett. 94 (1983) 609, M. Śliwińska-Bartkowiak, Ber. Bunsengess. Phys. Chem. 94 (1990) 64, M. Śliwińska-Bartkowiak, Phys. Lett. A 128 (1988) 84]. For such a system, we performed Monte Carlo simulations aimed at analyzing the kind of phase transition observed, and their conditions of their occurrence in a Lennard-Jones mixture. The enthalpy, configurational energy and radial distribution function have been estimated by the MC simulation method in the NPT system. Immiscibility conditions according to Hoheisel [M. Schoen, C. Hoheisel, Mol. Phys. 57 (1986) 65] approach have also been discussed.     

Neutron brillouin scattering in a metallic glass

The dispersion of collective modes in a metallic glass (Mg₇₀Zn₃₀) measured previously at the thermal neutron time-of-flight spectrometer, IN4, of the HFR of the ILL has been extended towards lower momentum transfers, down to the first pseudo-Brillouin zone, for the first time. This extension to momentum transfers not accessible up to now was possible using the high-resolution time-of-flight spectrometer, HET, at the new spallation source, ISIS. In the region of overlap, the two parts of the dispersion determined with different samples of the same metallic glass on different instruments agree very well. Also, the earlier discrepancies with the dispersion determined for this metallic glass from a computer simulation have been almost completely eliminated due to a more recent and more complete investigation.     

利用辐射加热炉进行蓝宝石及其它高温氧化物的热物理和光学性能的研究

本文描述了一种特大的实验装置-辐射加热炉,获得了蓝宝石和其它高温氧化物在固相、液相时的光学、热学和物理性能.该装置和相应的技术使得在高于3500K温度下研究这些材料的粘度、熔点、热导率、发射率和吸收系数成为可能,并以此得到了高温下蓝宝石的分子热传导系数,以及不同降温速率下蓝宝石的过冷情况.此外,介绍了一种复合氧化物材料MgO-Al2O3-HfO在宽波段范围内的反射率.本文所给出的数据对于从事晶体和高温陶瓷方面研究的专家学者将很有用处.     

On the Debye‐Waller factor and Debye temperature of CdO nanoparticles

Theoretical calculation on the phonon dispersion of CdO nanoparticles at room temperature is reported here for the first time. The mean square amplitude, Debye–Waller factor and Debye temperature are calculated for CdO nanoparticles from the phonon spectrum and compared with the experimental results obtained from Rietveld refinement of XRD pattern of the CdO nanoparticles. The thermal stability of the nanoparticles is studied from both the experimental and theoretical calculations of melting point which is found to be 3686 K and 3951 K, respectively, greater than that of bulk CdO. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Distinct property effects on rapid solidification of a thin liquid layer on a substrate subject to self-consistent melting

Heat transfer of a molten splat in a thin layer rapidly solidified on a cold substrate subject to self-consistent melting and distinct thermal and physical properties has been numerically investigated. Micro-electro-mechanical systems, semi-conductor technology, splat cooling, plasma or powder spray deposition, single and twin-roller melt spinning, strip and slab casting, melt extraction, etc. are usually characterized by rapid solidification of a thin liquid layer on a cold substrate. This work has proposed that the one-dimensional rapid freezing in the splat is governed by nonequilibrium kinetics at the solidification front while the melting in the substrate is determined from the traditional phase change condition. The results show that to delay the freezing of the splat and accelerate the melting of the substrate, an increase in the splat-to-substrate specific heat ratio and decreases in Stefan number, dimensionless solid conductivity of the substrate and substrate-to-splat density ratio are suggested. The freezing of the splat and melting of the substrate are delayed by increasing dimensionless initial temperature and decreasing dimensionless nucleation temperature of the splat. An early melting of the substrate while maintaining the same onset time for the freezing of the splat can be achieved by increasing the dimensionless kinetic coefficient and equilibrium melting temperature of the splat and decreasing the dimensionless equilibrium melting temperature of the substrate. The effects of the parameters on enthalpies and interface velocities in the splat and substrate are also presented.     

Compensation for the spectral dispersion of light polarization states in electro-optic modulators based on chiral liquid crystals

The effect of compensation for the spectral dispersion of light polarization states at the output of a single-domain layer of a chiral liquid crystal (CLC) is experimentally studied. It is shown that such dispersion can be decreased significantly with the aid of phase plates of two types that have different signs of the spectral dispersion of birefringence. The dispersion compensation allows one to significantly increase the operating spectral range of fast light modulators based on chiral nematic liquid crystals (NLCs).     

Physical chemistry of binary organic eutectic and monotectic alloys; 1,2,4,5-tetrachlorobenzene−β-naphthol and 1,2,4,5-tetramethylbenzene-succinonitrile systems

Phase diagrams of 1,2,4,5-tetrachlorobenzene–β-naphthol and 1,2,4,5-tetramethylbenzene–succinonitrile systems which are organic analogues of a nonmetal–nonmetal and a nonmetal–metal system, respectively, show the formation of a simple eutectic (melting point 103.7°C) with 0.71 mole fraction of β-naphthol in the former case and a monotectic (melting point 76.0°C) with 0.07 mole fraction of succinonitrile and a eutectic (melting point 52.5°C) with 0.97 mole fraction of succinonitrile in the latter case. The growth behaviour of the pure components, the eutectics and the monotectic studied by measuring the rate of movement of the solid–liquid interface in a capillary, suggests that the data obey the Hillig–Turnbull equation, v=u(ΔT)ⁿ, where v is the growth velocity, ΔT is the undercooling and u and n are constants depending on the nature of the materials involved. From the values of enthalpy of fusion determined by the DSC method using Mettler DSC-4000 system, entropy of fusion, interfacial energy, enthalpy of mixing and excess thermodynamic functions were calculated. The optical microphotographs of pure components and polyphase materials show their characteristic features.     

Radiative Heat Transfer in a Resistance Heated Floating Zone Furnace: A Numerical Study with FIDAPTM

This paper presents a numerical study of radiative heat transfer in a floating zone (FZ) furnace which was performed by using the commercial finite element program FIDAP^TM. This resistance furnace should provide a temperature higher than the melting temperature of silicon (i.e. T_max ≈ 1500 °C) and a variable temperature gradient at the liquid/solid interface (≥ 25 K/cm). Due to the high working temperatures, heat radiation plays the dominant role for the heat transfer in the furnace. For this reason, the quality of view factors used in the wall‐to‐wall model was carefully inspected with energy‐balance checks. A numerical model with two control parameters is applied to study the influence of material and geometrical parameters on the temperature field. In addition, this model allows us to estimate the internal thermal conditions which were used as thermal boundary conditions for partial 3D simulations. The influences of an optical lens system on the radial symmetry of the temperature field were examined with these partial 3D simulations. Furthermore, we used the inverse modeling method to achieve maximum possible temperature gradients at the liquid/solid interface according to the limitation of maximum available power and the maximum stable height of a melt zone.     

On the number of amorphous phases in n-butanol: Kinetics of free radicals oxidation by oxygen in frozen n-butanol

We report on the discovery of a new solid, presumably amorphous n-butanol at ambient pressure. According to the literature data the melting point T_m of n-butanol is 183 K and the glass transition temperature T_g is 118 K. If kept isothermally at a fixed temperature between 130 and 160 K, the supercooled liquid n-butanol undergoes remarkable phase transformations to a solid phase. The new phase converts to liquid at a temperature of about 170 K. It is presumably amorphous because foreign substances dissolved in liquid n-butanol keep the same state in this new phase of butanol. The kinetics of free radical oxidation by dissolved oxygen in both solid amorphous phases is investigated in detail.