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.     

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.     

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.     

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.     

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)     

Defects in quartz crystals initiated during their hydrothermal growth

A complex investigation (performed by means of X-ray topography, γ-ray diffractometry, optical methods) of the defects in as-grown and tempered quartz single crystals has been described. The results should contribute to the improvement of the quality of hydrothermally synthetized quartz.     

The dependence of cobalt concentration on the growth temperature in synthetic blue quartz

Co-doped blue quartz crystals were grown hydrothermally in an Na₂CO₃ solution. The concentration of cobalt in as-grown quartz crystal was observed to be independent of the concentration of cobalt in the nutrient but to be strongly affected by the growth temperature. It is concluded that transparent dark-blue quartz could be grown in the narrow temperature range, that is, 340–345°C. From TEM observations, the origin of the blue color in synthetic blue quartz is thought to be an inclusion effect resulting from the entrapped clusters of Co–Si–OH colloids, which is different from other reports [Wood, Ballman, Am. Mineral. 51 (1966) 216; Lehmann, J. Phys. Chem. Solids 30 (1969) 395]. The as-grown synthetic blue quartz crystal was jewel grade.     

Revelation of microtwinning in hydrothermally grown synthetic quartz by growth structures

Growth structuress on prism surfaces of synthetic quartz grown by hydrothermal crystallization technique, indicative of microtwinning in them are described, illustrated and discussed. The microtwins are revealed by the misorientation of the growth structures, and it is observed that microtwinning is manifested in different forms. Twinned domains appear in the form of strictly oriented, square striated (stepped) structures with inclined surfaces, seemingly overlapping square striated structures, square and irregular regions demarcated by black line-like boundaries, patch-like structures enveloping irregularily bound domains, tongue-like terraces bordered by irregular line of discontinuity of varying height and the regions with both differently shaped as differently oriented growth structures. From the orientations of the square shaped growth structures, it is shown that crystals consist of domains which are in twin relationship to the main crystal. Twins by rotation around an axis perpendicular to (10ī0) with rotation angles of 60°, 90°, and 180° have been observed. Critical examination of some twin boundaries delineated by black line-like matter, with the application of multiple beam interferometry and FECO reveal that the black boundary is a ridge (line-elevation). The line elevation along such a twin boundary is explained to be as a result of preferential adsorption of impurity atoms along the trace of the boundary. It is further observed that discontinuity in crystalline structure along the twin boundary leads to growth forms with distorted morphology thus establishing strong dependence of growth forms on the underlying crystalline structure. Causes for generation of the microtwins (twinning on a microscale) in synthetic quartz are discussed.     

Vapour growth and epitaxy of minerals and synthetic crystals

Surface microtopographs of the following crystals, both natural and synthetic, grown from pure vapour phase (PV), by chemical vapour transport (CVT), from high temperature solution (HTS) and hydrothermal solution (HS) are compared according to the criteria of (1) whether spirals are circular or polygonal and (2) how wide is the step separation of the spiral; SiC (PV, CVT, both synthetic), hematite (CVT, HTS, natural and synthetic), corundum (CVT, HTS, synthetic), mica minerals (PV, CVT, HS, natural and synthetic) and beryl (CVT, HTS, HS, natural and synthetic). Clear differences in morphology and step separation were found between crystals grown from vapour phase and solutions, between PV and CVT, as well as between natural and synthetic crystals. The differences are analysed in conjunction with the recent developments of computer simulations on spiral morphology. The results show interaction between solid and fluid plays very important role in determining the spiral morphology. Oriented intergrowth between different crystals well known among minerals, such as epitaxy, topotaxy, co-axial intergrowth, exsolution etc. are briefly summarized. It is also briefly explained how these relations are used in understand the growth or cooling histories of natural minerals.     

Direction change of dislocations on passing a growth sector boundary in quartz crystals

The behaviour of dislocations in quartz crystals changing their direction while passing from one growth sector into another where studied with X-ray topography. The investigations were performed on crystals which had been grown in c direction from seeds cut from different growth sectors. The dislocations are newly arranged according to KLAPPER 's theory, when they enter a growth sector with a different direction.     

The pAl0.7Ga0.3As-pGaAs-nGaAs concentrator cell with electrolytical contacts

The technological procedure involved in making p-Al_0.7Ga_0.3As-p-GaAs-n-GaAs concentrator solar cells by forced cooling LPE is discussed. Electrical contacts were electrochemically deposited from acid baths of Au and Ni, followed by annealing. 1.4 A/cm² short current densities and 1 V open circuit voltages were measured under 7 W/cm² incident radiation.     

X-ray investigation of H2-annealed quartz crystals

This paper investigates the variation of reflection properties of nearly perfect quartz crystals after annealing in H₂-atmosphere. Annealing at 800 °C causes a strong distortion of the lattice structure. Double-crystal diffractometer measurements show an approximate tenfold increase of the integral reflection coefficient. The reflection properties change homogeneously over the whole crystals.     

The growth of HgI2 crystals

The paper presents a system for αHgI₂ crystal growth by the temperature oscillation method. The system has a capability of crystal growing at an excess I₂ or Hg vapour pressure. Optimum conditions for producing crystals up to 2 cm³ by volume have been established. The crystals grown at an excess I₂ vapour pressure have higher resistivity and higher drift electron and hole mobilities — μ_e = 120 cm² V⁻¹ s⁻¹ and μ_h = 6 cm² V⁻¹ s⁻¹, respectively.     

The structure and properties of quartz crystals grown from fluoride solutions: Part II. The burgers vector of the growth screw superdislocations

Crystallography Reports - The birefringence method is used to investigate the distribution of microstresses around screw superdislocations with a hollow core in quartz crystals and to determine the...     

A possibility for improvement of the quality of quartz crystals

Experiments intended to improve the quality of seed plates for hydrothermal synthesis of quartz crystals have been performed. The plates were subjected to electro-sweeping of alkali cations. More perfect crystals were grown on such seeds.     

Circular dichroism spectra of synthetic amethyst crystals

The axial circular-dichroism spectrum of a synthetic amethyst crystal has been studied for the first time. Bands both of the positive and negative signs are revealed. New information on the color centers of amethyst and their electronic structure is obtained.     

The quality control of quartz growth: A chinese perspective

The quality of synthetic quartz crystals grown hydrothermally mainly depends on the average growth rate. A mathematical model of the growth rate based on a very large number of experiments has been established. This model is highly suitable for estimating the growth rate, the period and the output of each type of quartz crystal according to the technical design parameters, and plays an important role in the administration of product and the quality control in quartz crystal growth.