Chemistry in Lasers. VI. Dimeric Luminophors in Electrogenerated Chemilumines cence

Electrogenerated chemiluminescence (ECL) provides an unusually attractive method for producing dimeric luminophors, by comparison to optical pumping of a dye laser, both in terms of dimer/monomer ratio and variety of accessible states. Several dimeric luminophors arising from the homogeneous charge transfer step are discussed, and the customary assignment of full singlet or triplet character to some of the excited moieties is shown to be unwarranted. An error in the literature concerning the kinetics of ECL-dimer formation is pointed out.     

Frustrated percolation,spin glasses and glasses

Summary The static and dynamic properties of the frustrated percolation model are investigated. This model, which contains frustration as an essential ingredient, exhibits two transitions: a percolation transition at a temperatureT _p with critical exponents of the ferromagnetic (s=1/2)-state Potts model, and a second transition at a lower temperatureT _g in the same universality class of the Ising spin glass model. AboveT _p the time-dependent autocorrelation function is characterized by a single exponential, while forT _p>T>T _g preliminary numerical results show a broad shoulder or plateau typical of a structural glass transition. BelowT _g the system is in glassy state with an infinitely long relaxation time. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Supersolidity of glasses

The supersolidity of glasses is explained as the property of an unusual state of condensed matter. This state is essentially different from both normal and superfluid solid states. The mechanism of the phenomenon is the transfer of the mass by tunneling two-level systems.     

Orientational glasses

This review summarizes experimental evidence for the freezing of reorienting moments in solids. The moments may be of dipolar or quadrupolar nature, or both; they belong to one of the constituents of a mixed-crystal solid. Extensive results are reported for the following systems: KCl doped with hydroxyl, potassium tantalate doped with Li, Na and Nb, alkali halide cyanides and alkali-alkali cyanides, rubidium ammonium dihydrogen phosphate, solid ortho-para hydrogen and argon-nitrogen mixtures. These have clearly glass-like properties. In other systems, results are limited to one or two methods hinting at glass formation; some of those are also reported. Clustering phenomena and the slowdown of reorientations at the freezing temperature are observed in susceptibility measurements and by local probing on nuclear spins. The modulation of the structure by cluster formation is revealed by diffraction experiments. These phenomena are confronted with model predictions and numerical simulations.     

Fullerene glasses

We present the phase diagram of (C₆₀)_1-x(C₇₀)._x alloys, obtained from low frequency (1Hz) elastic and thermal expansion measurements. Whereas thermal expansion measurements show only a. fcc to sc phase transition in C₆₀-rich and a hcp to a distorted hcp phase transition in C₇₀-rich samples, low-frequency (1 Hz) elastic compliance measurements show an additional dynamic anomaly for all the samples (except for the pure C₇₀) due to freezing of the molecular motion. This anomaly is centered around T_g≈ 120 K for the pure C₆₀ and rises with rising concentration of C₇₀, reaching T_g ≈ 150 K for mixtures with 95mol% C₇₀. For C₇₀-rich samples with more than 10mol% C₆₀ no orientational phase transition was found. The phase diagram can be described in terms of the orientational glass model.     

超稳定玻璃

非晶态物质处于热力学非平衡状态,稳定性是非晶态材料应用的重要瓶颈,也是理论研究的关键问题.最近人们开发出相当于普通金属玻璃退火上百万年的"超稳定玻璃",为研究非晶态材料的稳定性和非晶态物质的本质提供了新契机.本文简要介绍超稳定玻璃的特点、形成机理以及其对非晶态物理学基本问题提供的新见解和新思路.     

Spin glasses

Recent developments in the theory of spin glasses are discussed. There has been considerable progress, due to Parisi, Sompolinsky, and others, towards understanding the infinite range (mean field) model of Sherrington and Kirkpatrick. Relaxation times diverge in the thermodynamic limit, and this nonergodic behavior is now understood to be the cause of earlier difficulties. There has been less progress in the study of more realistic models with short-range interactions, but numerical studies have shown rather clearly the absence of a finite temperature transition in two dimensions. There is probably no transition ind=3 either, though the evidence is less clearcut, which makes it difficult to understand the sharpness of the freezing observed experimentally. Well below the freezing temperature ESR and torque measurements have been fairly well explained by a theory of Henley, Sompolinsky, and Halperin, in which an important ingredient is anisotropy due to the Dzyloshinsky-Moriya interaction proposed by Fert and Levy.     

Orientational glasses

This review summarizes experimental evidence for the freezing of reorienting moments in solids. The moments may be of dipolar or quadrupolar nature, or both; they belong to one of the constituents of a mixed-crystal solid. Extensive results are reported for the following systems: KCl doped with hydroxyl, potassium tantalate doped with Li, Na and Nb, alkali halide cyanides and alkali-alkali cyanides, rubidium ammonium dihydrogen phosphate, solid ortho-para hydrogen and argon-nitrogen mixtures. These have clearly glass-like properties. In other systems, results are limited to one or two methods hinting at glass formation; some of those are also reported. Clustering phenomena and the slow-down of reorientations at the freezing temperature are observed in susceptibility measurements and by local probing on nuclear spins. The modulation of the structure by cluster formation is revealed by diffraction experiments. These phenomena are confronted with model predictions and numerical simulations.     

月球玻璃

玻璃是月壤的重要组成部分,由月球上火山喷发、陨石撞击和太阳风及宇宙高能射线辐照等一系列非平衡过程产生。玻璃可以在月球严苛的环境中长时间稳定存在,就像一帧帧的摄影快照一样记录着月球亿万年间的重要历史信息,涉及到月球的起源与演化、月球上水和气体的来源与分布、太阳系内的撞击历史和太空风化等重大科学问题。玻璃还能够长期保存各种月球物质,如太阳风注入的³He、反应生成的水和纳米铁等,影响着月球资源的利用和遥感观测。文章通过对嫦娥五号月壤玻璃的研究,阐述了各种月球玻璃的特征和形成机制,以及不同玻璃可能记录的月球历史信息。月球玻璃的研究也将为未来的星际探索提供宝贵的知识,并且帮助人们设计和制备新型的玻璃材料。     

Dynamics of proton glasses

The effects of random fields on the soft-spin dynamics of an Ising spin glass with infiniterange interactions are studied in the vicinity of instability line separating the ergodic and nonergodic phase.     

Properties of yttrium-iron-metalloid glasses

We report the results of measurements on metallic glasses of the form Y₆₆(Fe_1–x M _x )₃₄. For M = B we find that there is an extended range of glass formation (0x0.40) and that properties such as atomic density, electrical resistivity, microhardness, and thermal stability are functions ofx. For M = C, Si, or Ge we find a restricted range of glass formation (0 x0.10) and no significant changes in the properties of the glasses. Using Fe⁵⁷ Mössbauer effect spectroscopy we find that the M = B case is again unique in that the structure of the glass is sensitive to B content. We relate the differences in glass formation for the M = B and M = C, Si, Ge glasses to the existence of Y rich compounds in the C, Si, and Ge cases and the lack of such compounds in the M = B case.     

块体金属玻璃

在2013年2月出版的Physics Today杂志上刊登了耶鲁大学Jan Schroers教授撰写的题为《块体金属玻璃》的文章,重点介绍了块体金属玻璃优异的类似塑料一样的加工变形能力,并且对未来金属玻璃材料的研究和应用进行了展望. 制备一块金属玻璃就像与一个热力学的时钟赛跑一样.当金属液体冷却到熔点TM以下时,这个时钟开始活动.     

金属玻璃的稳定性

玻璃态材料自诞生以来一直受到自身稳定性的困扰。为了保障玻璃的服役安全性,人们一直努力提高玻璃的耐久性和稳定性。玻璃能否经年累月地保持长期稳定？影响其稳定性的物理机制和根源是什么？这些都是非晶态物理领域长期关注的重要难题。根据以往对非晶合金稳定性的研究结果,文章将简单介绍玻璃亚稳性的起源,然后介绍玻璃如何能够保持长期稳定,如何提高玻璃的热力学和动力学稳定性以制备出超稳玻璃,最后介绍影响玻璃稳定性的材料因素,用于指导有效地获得高稳定性玻璃。对玻璃稳定性的认识和理解,既能够保障玻璃材料服役过程中的安全性,又对认识过冷液体和玻璃转变等基本物理问题非常关键。