Vibrational spectra of crystals of bismuth borates

The vibrational spectra of crystals of bismuth borates Bi₂₄B₂O₃₉, Bi₄B₂O₉, BiBO₃, and Bi₂B₈O₁₅ were obtained for the first time, and the spectra of Bi₃B₅O₁₂ and BiB₃O₆ crystals measured in the range 30–1600 cm^?1 at room temperature were refined. The lines observed were assigned to the corresponding vibrational transitions on the basis of the theoretical group analysis and comparison of the obtained results with the vibrational spectra of borates of different composition. The complication of the structure of bismuth borates with increasing content of B₂O₃ was traced by the example of vibrational spectra.     

Dielectric relaxation in vitreous borates at low temperatures

Dielectric relaxation measurements have been made in vitreous alkali borates from 4.2 to 300 K, and from 10² to 10⁵ s^?1. Two types of relaxation are present: the first, at about 25 K (10³ s^?1), is intimately related to the presence of tetrahedral BO₄ units in distorted positions, and the second, at about 160 K (10³ s^?1), is correlated with water that is present in small quantities in glass.     

Crystal growth of barium aluminum (gallium) borates

Crystals listed in the JCPDS card in the BaO‐B₂O₃‐Al₂O₃ and BaO‐B₂O₃‐Ga₂O₃ systems are of interest from a viewpoint of the Second Harmonic Generation (SHG). Ba₅Al₄B₁₂O₂₉ and Ba₅Ga₄B₁₂O₂₉ are promising new crystals with SHG activity and with congruent melting mode. These crystals can be grown by the Czochralski method with a size of 3 × 3 × 0.1‐1mm. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of magnesium borates using sodium borate and magnesium sulfate

Synthesis conditions of magnesium borate compounds in aqueous medium using Na₂B₄O₇ · 10H₂O and MgSO₄ · 7H₂O were determined. The effects of B/Mg mole ratio, pH, reaction time and precipitation temperature on the reaction performed at 90 °C were examined. 0.04Na₂O · MgO · 1.23B₂O₃ · 3.42H₂O and 0.06Na₂O · MgO · 1.65B₂O₃ · 3.34H₂O were synthesized at optimum B/Mg mole ratios of 3.60 and 4.80 by precipitation at 5 °C and the amorphous compounds formed were identified by B, Mg, Na and XRD analyses and some physical tests.     

晶体的超精密抛光

超光滑表面在现代科学技术中具有重要意义.超精密抛光技术是实现超光滑表面的主要方法.本文对超光滑表面的概念、影响超精密抛光质量的因素、几种超精密抛光方法及其所能达到的抛光效果、抛光效果的测量与评价方法等进行了介绍.同时描述了超精密抛光的发展阶段、现状和发展趋势.     

Characterization of SHG candidate crystals in barium aluminum (gallium) borates

Crystals listed in the JCPDS card in BaO‐B₂O₃‐Al₂O₃ and BaO‐B₂O₃‐Ga₂O₃ systems were synthesized by means of a solid‐state reaction method and a liquid‐state reaction method. Synthesized crystals were characterized from a viewpoint of Second Harmonic Generation (SHG) and crystal growth possibility. Ba₅Al₄B₁₂O₂₉ and Ba₅Ga₄B₁₂O₂₉ are promising new candidate crystals from the viewpoint of SHG activity and congruent melting behavior. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nomenclature of Liquid Crystals

Abstract

One of the signs of the maturing of a new area of knowledge is a heightened discussion and awareness of nomenclature, conventions and labels. In emerging sciences, the facts are often in dispute or open to different interpretations, and so premature attempts to categorize and standardize will only serve to confuse and delay real understanding. Liquid crystal science is now of an age when the attention of its practitioners is being drawn to considerations of nomen-clature. Indeed in 1997 IUPAC (International Union of Pure and Applied Chemistry) issued provisional recommendations concerning the definition of basic terms and symbols for liquid crystals. Members of the International Liquid Crystals Society have become involved with the preparation of a final document, which hopefully will be generally accepted and followed by scientists in the field. Some of the initial recommendations have already been reported in the new Handbook of Liquid Cryrstals, published in 1998 [1], so the process of formalising the nomenclature of liquid crystals has begun.     

人工晶体的发展

本文扼要地综述了20世纪后半叶人工晶体发展的简况,其中包括块状晶体、薄膜晶体、纤维晶体、纳米晶体.最后在已取得成就的基础上,展望了人工晶体发展的未来.     

人工晶体发展动向的探讨

本文评述了人工晶体在体块大单晶生长、薄膜的外延生长,微结构和光子晶体、微米晶和纳米晶等方面的新近发展,并对未来的智能晶体进行了讨论.     

Liquid Crystals Tomorrow

Abstract

This issue of Liquid Crystals Today is slimmer than usual, and so provides an excuse for an editorial. Copy for Liquid Crystals Today comes through a variety of channels: some items are sent unsolicited to the editor or members of the editorial board, while feature articles are often written as a result of one of the editorial team reading or hearing about some new development in liquid crystal science. The flow of contributions is, therefore, random, and one of the tasks of the editor is to try to ensure that, from this random flow, a steady stream of high quality material emerges to coincide with the publication dates. This time it hasn't happened, so rather than wait for articles in the pipe-line, we have decided to publish a thin edition of Liquid Crystals Today. We do have some excellent articles being prepared, and we expect to publish an extended edition next time to include these.     

Carbohydrate Liquid Crystals

Certain alkyl l-O and l-S glycosides with hydrocarbon chain lengths greater than hexyl have been shown to form thermotropic liquid crystals at temperatures between 60 and 100[ddot]C. These are believed to be members of a large class of alkyl and acyl carbohydrate mesogens which, apart from their intrinsic value as potentially useful solid-state materials, could provide a variety of structurally accessible model systems for studying the phase transitions in the cell-membrane glycolipids.     

Crystals for photonics

Crystallography Reports - The prospects of using crystals in photonics are discussed. Primary attention is focused on one of the topical problems of photonics—creation of sources of laser...     

Polymer Liquid Crystals

Abstract

The field of polymer liquid crystals is encompassing an increasingly wide range of research areas and applications, as was demonstrated at a recent one day meeting devoted to the subject. The meeting was held in London at the Scientific Societies Lecture Theatre, and was organized by the Institute of Physics Polymer Physics Group and co-sponsored by the British Liquid Crystal Society and the Royal Society of Chemistry.     

Ferroelectric Liquid Crystals

A review of the ferroelectricity in liquid crystals is given, beginning with a discussion of the symmetry properties allowing a macroscopic polarization in some of the more ordered liquid crystal phases. The fundamental mechanisms behind the dipolar ordering are discussed in some detail. The two linear electric effects, ferro- and flexo-electricity, give rise to completely different phenomena. In the smectic C phase there is one ferroelectric coefficient and nine flexoelectric ones, giving independent contributions to the polarization of the medium. We further discuss helical and non-helical structures, doped and intrinsic infinite-pitch ferroelectrics and, finally, the rich potential of liquid crystal ferroelectrics aligned in the »book-shelfgeometry» for fast electro-optic devices.     

晶体材料研究——从体块晶体到微纳米晶体

本文首先简要介绍了晶体的重要性和过去几十年来中国晶体材料研究取得的代表性成果.正文主要以我们课题组开展的工作为例,介绍了激光晶体、非线性光学晶体、磁光晶体、声光晶体、半导体晶体、有机晶体、有机-无机复合晶体、二维晶体、单晶光纤、药物结晶、微纳米晶体等方面的研究进展.这些研究实例的维度已覆盖体块-二维-一维-零维,晶体材料已在国防、经济建设、人类健康和科学技术发展的许多领域,发挥了重要作用并仍将是关键材料.     

Polymorphism of Compound Existing as Both Racemic Compound Crystals and Mixed Crystals of Enantiomers

Abstract

By recrystallization of certain racemic compound (ST), racemic compound crystals, mixed crystals of two enantiomers, or a mixture of these two types of crystals were obtained, depending on the recrystallization conditions employed. Their crystal forms were determined by X-ray diffraction of the single crystals and powdered materials. The space group and lattice parameters of the mixed crystals were identical with those of the enantiomeric crystals. This polymorphism of ST crystals would be ascribed to the small difference in the thermodynamic stability between the enantiomeric and racemic crystals. The physicochemical properties of ST are described, too.