A phenomenological approach to relaxation in disordered systems

We propose a phenomenological approach to relaxation in disordered systems which is modelled after the well-known percolation behaviour. The approach shows an interesting behaviour of the time correlation function of relevant variables which is characterized by three temporal regimes, an initial exponential decay, a power-law regime and a stretched exponential decay for long times. We give some relevant examples of this behaviour in a wide variety of systems such as gels, microemulsions and glasses.     

DSC study and computer modelling of the melting process in ice slurry

In order to understand the non-isothermal melting kinetics in the ice slurry, a differential scanning calorimetry (DSC) was used. Experimental results were compared to those obtained by a numerical simulation in which a general enthalpy method was applied. In this work the ice slurry studied consists of ice particles uniformly dispersed within a water-antifreeze liquid mixture. The effects of the heating rate and the initial antifreeze mass fraction are discussed. It has been found that the temperature gradients inside the sample of the solution become important if either heating rate increases or initial antifreeze mass fraction decreases.     

ICP-MS 法直接测定冰芯样品中超痕量镉

采用 ICP- MS法对冰芯样品中超痕量 Cd的直接测定进行了研究。确定了直接测定浓度为 pg/m L 级的 Cd的最佳仪器参数、载气流速、进样速度等与灵敏度之间的关系以及浓度和扫描参数对分析精度的影响。本方法对浓度 5～2 0 0 pg/m L Cd的分析 ,RSD<1 0 % ,回收率在 88%～ 1 0 5%之间 ,检测限为0 .1 5pg/m L     

Effect of transition metal doping and carbon doping on thermoelectric properties of YB66 single crystals

We have been investigating the high-temperature thermoelectric properties of some novel rare earth borides with a structure containing B₁₂ icosahedra. Doping effects on the TE properties in such systems were investigated for the first time. A series of Nb-doped YB₆₆ and C-doped YB₆₆ single crystals were grown by the floating zone method. The Nb-doped compounds have approximate chemical formulas ranging from YNb_0.30B₆₆ to YNb_0.33B₆₆ while the C-doped compound has a formula of YB₆₆C_0.6. The effect of Nb-doping on the thermoelectric properties was not monotonic and appears to be complex. As a result of Nb-doping, the room temperature resistivity and the characteristic temperature T₀ were considerably reduced. At room temperature the power factor of the Nb-doped YB₆₆ sample with 89% site occupancy was three times greater than that of non-doped YB₆₆. However, in the important high-temperature region, the non-doped sample actually exhibited the highest power factor for . Furthermore, owing to a structural feature of YB₆₆, thermal conductivity actually increases with doping of transition metals. Taking into account all the thermoelectric properties, transition metal doping of YB₆₆ is therefore not suitable for our purposes. On the other hand, doping of carbon, which is assumed not to go into the same sites as the transition metals, yielded a lowering of the thermal conductivity. Furthermore, contrary to Nb-doping, carbon doping did not result in a reversal of the relative magnitude of resistivity at extremely high temperatures and therefore, an increase in the figure of merit of factor 2 was realized at 1000 K.     

Micro-Raman mapping on an anatase TiO2 single crystal with a large percentage of reactive (0 0 1) facets

After it has been successfully synthesized in 2008, so far, no Raman investigations on the micro-sized anatase TiO₂ single crystal which has a large percentage of the reactive (0 0 1) facets have been conducted to the best of our knowledge. In the present work, this unique anatase TiO₂ single crystal was investigated by noninvasive and nondestructive Raman mapping technique. Raman images of both non-polarized and polarized measurements showed that the Raman features of the crystal varied with measurement position. The differences among the Raman spectra measured on different crystal facets were believed to result from the orientations and the symmetry rules. Whereas the differences among those measured at different points of the same crystal facet under the same measurement condition were supposed to indicate the defects of the crystal structure, such as oxygen vacancies, local lattice disorder etc. Furthermore, the appearance of the two second order Raman peaks of 803 and 918 cm⁻¹ as well as the blue-shift of 395 cm⁻¹ peak implies the anharmonicity of the crystal structure, which is also probably caused by the crystal defects. Our results provide useful information about the structure of this unique anatase TiO₂ material, and could be complementary to those that acquired by other characterization techniques.     

Significant Enhancement of the Upconversion Emission in Highly Er3+-Doped Nanoparticles at Cryogenic Temperatures

Relatively low efficiency is the bottleneck for the application of lanthanide-doped upconversion nanoparticles (UCNPs). The high-level doping strategy realized in recent years has not improved the efficiency as much as expected. It is argued that cross relaxation (CR) is not detrimental to upconversion. Here we combine theoretical simulation and spectroscopy to elucidate the role of CR in upconversion process of Er³⁺ highly doped (HD) UCNPs. It is found that if CR is purposively suppressed, upconversion efficiency can be significantly improved. Specifically, we demonstrate experimentally that inhibition of CR by introducing cryogenic environment (40 K) enhances upconversion emission by more than two orders of magnitude. This work not only elucidates the nature of CR and its non-negligible adverse effects, but also provides a new perspective for improving upconversion efficiency. The result can be directly applied to cryogenic imaging and wide range temperature sensing.     

Thermodynamics of water,vapor, ice,and seawater

The SCOR/IAPSO Working Group 127 was founded in 2005 and charged with the development of a new, comprehensive, highly accurate, and consistent standard formulation of seawater thermodynamics for oceanography. This task was approached in cooperation with the International Association for the Properties of Water and Steam (IAPWS) for a joint standard with industrial applications. In addition to the available standard for fluid water, IAPWS-95, new formulations for ice, IAPWS-06, and the thermodynamics of seawater, IAPWS-08, have been developed, supplemented by a redefinition of salinity, the Reference-Composition Salinity Scale 2008. In this paper the starting situation is described, the requirements to be met during the development process are studied, and the properties of the final formulations are briefly characterized.

红外辐射多相复合粉体常温发射率的提高及波段宽化

通过多相成分分析, 以镁铝硝酸盐、正硅酸乙酯、钛酸四丁酯和氧氯化锆等为原料, 采用溶胶\|凝胶燃烧法合成了新型复相氧化物粉体, 研究了Ni和Fe离子掺杂及粉体细化对红外辐射率的提高及波段宽化的影响. XRD物相分析发现, 在1100～1200 ℃范围内煅烧可获得结晶良好的氧化物粉体, 该粉体的结构为堇青石及金红石等多相结构. 采用碳酸氢铵为pH调节剂与使用氨水相比, 粒子中位粒径有显著减小. 红外辐射性能显示, 在1～22 μm的宽波段内, 该复合粉体均具有很高的红外发射率, 在10 μm附近其红外发射率达到98%. 同时Ni及Fe离子的掺杂及粉体细化可引起堇青石晶格畸变, 增强了材料的非简谐效应, 从而有利于复合粉体红外辐射率的提高.     

Laser induced breakdown spectroscopy of soils, rocks and ice at subzero temperatures in simulated martian conditions

We applied Laser Induced Breakdown Spectroscopy (LIBS) on moist soil/rock samples in simulated Martian conditions. The signal behavior as a function of the surface temperature in the range from + 25 °C to − 60 °C was studied at pressure of 7 mbar. We observed the strong signal oscillations below 0 °C with different negative peaks, whose position, width and magnitude depend on the surface roughness. In some cases, the signal was reduced for one order of magnitude with consequences for the LIBS analytical capability. We attribute such a signal behavior to the presence of supercooled water inside the surface pores, which freezing point depends on the pore size. On a same rock samples with different grades of the surface polishing, the signal has different temperature dependence. Its decrease was always registered close to 0 °C, corresponding to the freezing/melting of normal disordered ice, which can be present inside larger pores and scratching. An amount of the signal reduction at the phase transition temperatures does not seem to change with the laser energy density in the examined range. Comparative measurements were performed on a frozen water solution. A large depression, for two orders of magnitude, of the LIBS intensity was observed close to − 50 °C. The same negative peak, but with a smaller magnitude, was also registered on some rock/soil samples. Ablation rates and plasma parameters as a function of the sample temperature are also discussed, and their consequences for in-situ analyses.     

Symposium overview computer simulation of inorganic solids

Summary A symposium on Computer Simulation of Inorganic Solids, organised by the Applied Solid State Chemistry Group Trust and by the Polar Solids Group of the Royal Society of Chemistry was held in London, in December 1988. Speakers at the forefront of research in computational techniques for simulation of inorganic solid materials reviewed the range of application of these methods and the prospects for future application to a largely non-specialist audience.The meeting was timely and well supported. The majority of the talks given are presented in this volume. This overview discusses the recent expansion of interest in solid state chemistry and the important role that computer simulation methods have played in this growth. The papers are summarised with especial reference to recent developments in solid state chemistry and materials science.     

A Twist‐Bend Nematic Phase Driven by Hydrogen Bonding

The liquid crystalline phase behavior of 4‐[6‐(4′‐cyanobiphenyl‐4‐yl)hexyloxy]benzoic acid (CB6OBA) and 4‐[5‐(4′‐cyanobiphenyl‐4‐yloxy)pentyloxy]benzoic acid (CBO5OBA) is described. Both acids show an enantiotropic nematic phase attributed to the formation of supramolecular complexes by hydrogen bonding between the benzoic acid units. In addition, CB6OBA provides the first example of hydrogen bonding driving the formation of the twist‐bend nematic phase. The observation of the twist‐bend nematic phase for CB6OBA, but not CBO5OBA, is attributed to the more bent molecular shape of the complexes formed by the former, reinforcing the view that shape is a key factor in stabilizing this new phase. Temperature‐dependent FTIR spectroscopy reveals differences in hydrogen bonding between the two nematic phases shown by CB6OBA which suggest that the open hydrogen‐bonded complexes may play an important role in stabilizing the helical arrangement found in the twist‐bend nematic phase.     

The disorder of perfluoroalkyl chains in crystals: Two case histories of interpretation and refinement

Perfluoroalkyl chains in solids are highly disordered in a wide range of temperatures. Poor attention is typically given to this problem in crystallographic studies to the point that no attempt is frequently made in order to model the collected data and disorder remains even unmentioned in a large number of single crystal reports. This paper presents a short analysis of the problems related with this disorder. Two simple crystal structures, namely the halogen bonded adducts between N,N,N′,N′-tetramethyl-1,4-phenylendiamine and α,ω-diiodoperfluorobutane or α,ω-diiodoperfluorohexane are discussed in details in order to suggest some simple and basic principles for the refinement of perfluoroalkyl chains in single crystal structural studies.     

Crystal structure of a cholesterol-based dimesogen

The title compound, cholesteryl 6[4-(4-pentyloxyphenylethynyl)phenoxy]hexanoate (DMT5), a cholesterol-based dimesogen, crystallizes in the monoclinic space group P2₁ with the parameters a = 9.812(3) Å, b = 9.713(2) Å, c = 24.179(2) Å, β = 92.48(1)° V = 2302.2(9) ų, Z = 2, F₀₀₀ = 836, λ(MoK_α) = 0.71069 Å, μ = 0.067 cm 1, final R = 0.0772. The structure has intermolecular hydrogen bonds; it is stabilized by the presence of intermolecular contacts whose spacings are less than van der Waals' radii.     

A Hydrogen‐Bonded Framework Complex without Lattice Solvents: Synthesis Reversible Crystal‐to‐Amorphous Transformation and Chromic Properties

Reaction of Ni(NO₃)₂·6H₂O with H₄BPTC (H₄BPTC = Biphenyl‐3,3′,4,4′‐tetracarboxylic acid) produced a 3D hydrogen‐bonded framework complex 1 , not containing lattice solvents, with empirical formula [Ni(H₂O)₆]·H₂BPTC. The complex exhibits an interesting reversible crystal‐to‐amorphous transformation property unaccompanied by lattice solvents release/loading and shows selective and reversible chromic response to methanol.     

激光剥蚀电感耦合等离子体质谱法分析Cr∶ZnSe晶体中掺杂元素Cr的含量和分布

采用激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)法研究激光晶体材料Cr∶Zn Se晶体中掺杂元素铬(Cr)的含量和分布。利用镀膜扩散掺杂方法,制备不同掺杂浓度的Cr∶Zn Se晶体标准样品作为固体标准物质,实现Cr∶Zn Se晶体中Cr的定量分析。LA-ICP-MS法研究自制标准样品中Cr的分布均匀性,电感耦合等离子体光谱法测定其准确含量。通过激光点剥蚀和线扫描剥蚀采样,获得Cr元素的点位和含量分布信息,实现晶体中Cr的原位微区分析。标准工作曲线相关系数0.9992,检出限0.08 mg/kg。本方法可为不同生长条件下Cr∶Zn Se晶体中Cr的统计分布分析提供有效检测手段。     

Ultra-sensitive Flow Injection Analysis (FIA) determination of calcium in ice cores at ppt level

A Flow Injection Analysis (FIA) spectrofluorimetric method for calcium determination in ice cores was optimised in order to achieve better analytical performances which would make it suitable for reliable calcium measurements at ppt level.The method here optimised is based on the formation of a fluorescent compound between Ca and Quin-2 in buffered environment. A careful evaluation of operative parameters (reagent concentration, buffer composition and concentration, pH), influence of interfering species possibly present in real samples and potential favourable effect of surfactant addition was carried out. The obtained detection limit is around 15 ppt, which is one order of magnitude lower than the most sensitive Flow Analysis method for Ca determination currently available in literature and reproducibility is better than 4% for Ca concentrations of 0.2 ppb.The method was validated through measurements performed in parallel with Ion Chromatography on 200 samples from an alpine ice core (Lys Glacier) revealing an excellent fit between the two chemical series. Calcium stratigraphy in Lys ice core was discussed in terms of seasonal pattern and occurrence of Saharan dust events.     

The TV in Your Pocket: Development of Liquid‐Crystal Materials for the New Millennium

New liquid crystals with very low viscosity, good mesophase behavior, and high reliability are necessary to achieve the breakthrough from flat computer monitors to large displays for television. Fluorine plays a decisive role not only because of the polarity it induces in organic molecules but also because of its low polarizability and weak propensity for ion solvation. In addition, subtle stereoelectronic effects in fluorine‐containing liquid crystals influence material properties and allow these to be tuned to some extent to achieve the desired outcome. Some fairly sophisticated chemistry is required that is normally ruled out in the specialty chemicals industry because of cost. The television display market is now entering a phase of saturation. The broad availability of the internet has led to an ever increasing tendency for mobile products. Tablet PCs and smartphones require touch‐panel functionality and low power consumption. New LCD modes with high‐performance liquid crystals and additional components, such as polymerizable materials, can be used in such products.     

A Liquid Crystalline Oligomer Exhibiting Nematic and Twist‐Bend Nematic Mesophases

The twist‐bend nematic phase (N_TB) has been described as the structural link between the untilted uniaxial nematic phase (N) and the helical chiral nematic phase (N*). The N_TB phase exhibits phenomena of fundamental importance to science, that is, 1) the spontaneous formation of a helical pitch on the nanometer scale in a fluid and 2) the spontaneous breaking of mirror symmetry, leading to the emergence of chiral domains in an achiral system. In this Communication, we present a study on T4₉ [bis(4‐(9‐(4‐((4‐cyanobenzoyl)oxy)phenyl)nonyl)phenyl) 4,4′‐(nonane‐1,9‐diyl)dibenzoate], a liquid‐crystalline oligomer exhibiting the twist‐bend nematic phase, which has a molecular length that is of comparable dimensions to the sub‐10 nm pitch determined for CB9CB, and provide new insights into the differentiation between the nano‐ and macro‐science for self‐assembling supermolecular systems.     

Random nematic structures in the absence of inherent frustrations

We study the impact of anisotropic nanoparticles (NPs) on the nematic liquid crystal (LC) order. Within a mesoscopic Flory–Huggins-type approach we have estimated regimes where LC–NP mixtures are essentially homogenous. Using a lattice Lebwohl–Lasher type approach we have also studied the impact of anisotropic NPs on LC ordering. We analysed the cases where the orientations of NPs are either frozen-in or could be varied, to which we refer as random field mixtures and annealed mixtures, respectively. In the latter case we have demonstrated the existence of qualitatively different regimes. In particular, we determined the concentration regime, where LC configurations resembling a transparent nematic phase could be observed. Such domain patterns are stabilised by NPs hindering the annihilation of topological defects in LC order.