耐辐射优质石英晶体的生长

在水热条件下,我们利用三次再结晶的方法,生长了耐辐射优质石英晶体。随着再结晶次数的增加,晶体中的杂质浓度和缺陷浓度明显降低,晶体的耐辐射性能明显提高。     

Solid Inclusions in Man-made Quartz Crystals Electron Microscopic Investigation

Short-term hydrothermal experiments were carried out for a more detailed study of solid inclusions in man-made quartz crystals. In these experiments the crystals which usually are included in quartz occur on the surface of the seed and are only partly overgrown by quartz. Optical observations and SEM and EDS investigations have shown that: 1. The formation of inclusions is a special event in the history of autoclave growth of quartz, the process being controlled by the formation of many sites of increased surface tension. 2. Epitaxial phenomena are of great importance in the formation of inclusions. 3. The solid inclusions are of quartz (30%) and of the Na-Fe-silicate Phase 1 (70%). Both occur as single crystals larger than 3 μm as well as clusters of crystals smaller than 2 μm. 4. The several other phases observed as inclusions are of no importance for the quality of the man-made quartz crystals.     

Mechanism of Various Growth Morphologies of Kutch Quartz Crystals

Locations and estimated amounts of deposits of quartz crystals found in the Kutch district of Gujarat State, India are given. A report about various morphologies of these crystals in geodes is presented. Influence of supersaturation on the mechanism of formation of the initial, intermediate and final growth morphologies has been assessed. It is suggested that the changing growth morphology is a function of supersaturation value. Trapezium-shaped and semi-circular hillocks observed on the prism faces are described and discussed. It is proposed that these hillocks develop and grow in a sequential manner and like crystals have initially triangular form.     

A Model for Structures Growth by Sodium Electrodiffusion in Quartz Crystals

Dendritic structures were grown inside the quartz crystal by electrodiffusion of sodium ions from a NaCl layer at the anode. The electric field was applied along the optical axis Z and the structures were grown in the xy plane. An experimental arrangement using a pointed cathode and a graphite plate anode was employed. X ray diffraction analysis shows that the structures' chemical composition is a mixture of sodium silicates. To explain the structures' growth a model is proposed. The model is a bidimensional one. The transport of the particles along the Z axis structural channels by the electric field was taken into account by introducing a probability of generating the particles in the growth plane as a function of the distance to the cathode. The computer generated results and the experimental ones were compared and a good correlation was found.     

A Pragmatic Model for the Simulation of Self-induced Striations in Quartz Crystals

A mechanism is investigated which might lead to fluctuations in the growth of quartz crystals due to the periodic incorporation of impurities. The model ought to be applicable also to the incorporation of stoichiometric partners during the growth of complicated crystals from non-stoichiometric melts. The processes have been simulated with help of an equivalent circuit experimentally and by computation. Some typical cases are presented in the paper.     

X-ray topographic study of quartz crystals with induced growth striations

The method of “induced growth striations” was applied to the hydrothermal growth of quartz crystals. Striations were due to a periodical modulation of the growth temperature induced and investigated by means of the X-ray Lang topography and plane wave reflection topography. The results show that the X-ray topographic methods are a sensitive tool for the characterization of the growth striations, which are produced generally by Al impurities. The application of the method of induced growth striations to quartz crystals and the characterization of these crystals with optical and X-ray topographical methods allow a deeper understanding of the crystal growth behaviour.     

Magnetic Field Induced Deformations in Nematic Liquid Crystals

Abstract

Unlike most organic materials, liquid crystals respond readily to magnetic fields. This response originates in the anisotropic magnetic susceptibility of nematics, and the relative ease with which they undergo orientational deformations. Because of the large optical birefringence of liquid crystals, these orientational deformations are easy to observe. An interesting demonstration is to place a small rare earth magnet on a nematic cell between crossed polarizers which is illuminated from below. As the magnetic field reorients the liquid crystal, beautiful interference colours appear, indicating director deformations.     

The reversion of smoky quartz coloration in crystals with induced growth striations

Induced growth striations in quartz crystals grown from Al-containing material have been investigated after X-raying them. Earlier results (Bernhardt, Alter) showed that the stripes may occur as strong colored ones on a light background or as light stripes on high coloration background. This behaviour depends on the growth region regarded, and the applied X-ray dose. The position of the stripes may become displaced in dependence of the X-ray dose. The present paper developes a model which may describe this effect only using the diffusion law, the smoky quartz centre model according O'Brien and the Al³⁺/Na⁺-distribution in the crystal. Our results must be taken into account when interpreting the growth striations.     

Laser Induced Reorientation of Nematic Liquid Crystals

A significant increase of the divergence and appearance of a fringe system has been observed by illuminating of MBBA (p-n-methoxybenzilidene-p-butylaniline) and OCB (octyl-cyano-biphenyl) nematic liquid crystalline samples with a collimated beam of an argon ion laser. The dependence of this effect on laser power, beam polarization, and angle of incidence has been studied in homeopolar and planar sandwich-like cells of 50-150 μm thickness, in the nematic phase. At a homeopolar cell of MBBA (150 μm thickness), at normal incidence a threshold laser power of 45 m W was found. The phenomena can be explained as deformation of the orientation by the Fredericks effect due to light fields. The observations are in good agreement with the theoretical predictions including an estimation of the laser power threshold.     

The electrolytical coloration of synthetic quartz crystals with induced growth striations

Electrolytical coloration of quartz crystals with induced smoky quartz striations has been investigated, and compared with the arrangement of smoky quartz stripes after X-irradiation. Investigations have been made on z-, s-, −x- and +x-regions of the crystal after application of an electrolytical current in z-direction.     

Contrast formation in plane wave topographs of quartz crystals with induced growth striations

A qualitative and quantitative study of the contrast formation in X-ray plane wave topographs of quartz plates with induced growth striations is presented. Contrast distributions are calculated by means of a simple local application of the dynamical theory of the X-ray diffraction from the perfect crystal and using a mathematical model of the lattice deformation according to the isotropic theory of elasticity. A good agreement between calculations and experimental results can be stated.     

X-ray Lang Topography and Infrared Spectroscopy in Quartz Crystals Grown Hydrothermally with Intermittent Runs

Growth defects in Y-plates obtained from Y-bar synthetic quartz crystals, grown hydrothermally with intermittent runs, have been studied for the first time by X-ray Lang topography and infrared spectroscopy. To study the effect of interfaces on dislocation structures, the growth runs have been discontinued several (6 to 7) times by switching off the autoclaves from 30 min to 1 h. The dislocations were observed to change their directions at the generated interfaces, sometimes they stop at the in terfaces or move straight through the interfaces depending on the angles of the interfaces which are presumably low-angle grain boundaries. The percentage transmission of infrared beam has also been measured as a function of the distance traversed in the crystal. The inverse anelastic loss (Q) decreases at the interface which is due to the greater accumulation of chemical impurities and H bonded OH⁻ ions at these interfaces. The effect of in-situ electric field on the topographic contrast has also been studied which reveal some interesting results on account of space charge polarization.     

Effect of Thermal Treatment and Sweeping on the Electrical Conductivity of Quartz Crystals

The effect of thermal treatment and sweeping at different temperatures on the current peaks occurring during the heating-up phase of the electrodiffusion runs are studied. Arrhenius plots of swept synthetic quartz are discussed.     

Simulation of contrasts in X-ray plane wave topographs of quartz crystals with induced growth striations

Using system theoretical methods and fast discrete Fourier transforms, contrasts in plane wave topographs of crystals with impurity distributions of any form can be simulated with high accuracy and in a short time.     

The Influence of Interstitials and Growth Conditions on the X-Ray Colorability of Synthetic Quartz Crystals

The saturation colorability of quartz crystals depends not only on the contamination of the material but also on the regarded growth sector. But even in the same sector the colorability varies locally. Investigations of crystals with induced growth striations and defined local growth rate showed that the dependence of the colorability on the growth conditions is very complex. The growth rate to colorability characteristics may have positive or negative slopes regarding e.g. —x-or z-sections. Optical investigations of —x-sections prove that under certain circumstances light and/or dark striations may occur or even uncolorable regions may be observed, althought the contamination is sure. We explain this by the interaction of the coloration centres with interstitials. That effect might be of importance for the evaluation of the impurity by means of the coloration of natural or synthetic quartz crystals.     

Investigations of impurity striations in potassium bichromate crystals

Impurity striations in potassium bichromate crystals (KBC, lopezite) formed during crystal growth from aqueous solution were revealed by chemical etching and analyzed. Striations were revealed as etch grooves, as rows of dislocation etch pits and as rows of flat‐bottomed etch pits. Various types and groups of striations have been visualized. Some striations were due to lateral segregation of impurities caused by convection flow of the mother solution, other were formed during growth stoppages whereas induced striations were generated by changes in hydrodynamical conditions. Growth rates changes resulted in zonal distribution of impurities, formation of planar lattice strain, rows of clusters of point defects and rows of dislocations. Generation of striations with different intensities in various sectors is a proof of the selective capture of impurities. Ratios of growth rates of various faces of KBC crystals growing in forced and free convection regimes were determined by induced striations. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Initial Growth Stages of Man-made Quartz Crystals and Growth Mechanism of their (0001) Face

In a series of short term runs it has been shown that in the course of the non-stationary part of the hydrothermal process the quartz seed plate is subject to: 1. fast and deep dissolution; 2. very slow dissolution-and-growth; 3. a shallow complementary etching; 4. mass formation of crystallization centres; 5. tangential and normal growth of these centres accompanied by their aggregation into larger growth units. Every one of theses processes produces a specific structure on the actively growing (0001)-face. The last process which continues also when the temperatures are stationary, creates the well known “cobble structure”. As the growth continues the prolonged aggregation increases perceptibly the growth rate and makes the cobble structure coarser and coarser.