Microhardness of crystals of KBr-KI solid solutions with Sr2+ and OH− impurities

The microhardness, conductivity, and dielectric-loss angle have been studied in KBr and KI single crystals and in their solid solutions with Sr²⁺ and OH^– impurities. It is shown that the Sr²⁺ impurity dissolves only slightly in KI crystals and in KBr-KI solid solutions having a large KI content. Addition of the anionic OH^– impurity to the molten salts reduces the micro-hardness of KBr but it does not affect that of KI crystals or KBr-KI solid solutions having a large KI content. The composition dependence of the microhardness for KBr-KI solid solutions is constructed on the basis of the microhardness values for the corresponding crystals purified of cationic impurities of different valence.Translated from Izvestiya VUZ. Fizika, No. 10, pp. 18–21, October, 1969.     

Effect of magnetic treatment of KDP and ADP crystals and solutions on their equilibrium temperature

The effect of magnetic treatment of KDP and ADP crystals and solutions on their equilibrium temperature has been revealed and studied. The change in the temperature reaches a maximum immediately after the magnetization. Then, the effect decreases monotonically, and the equilibrium temperature approaches the equilibrium value for 5 h. It has been found that the observed decrease in the solubility depends on the impurity concentration, and it is maximum in magnetically treated KDP crystals with a chromium impurity; then, it decreases in the series: KDP crystal, KDP-ADP crystals in KDP-ADP solution, KDP crystal in KDP-ADP solution, and KDP solution. For all five systems under study, the relaxation times have been determined. It has been revealed that the effect rapidly increases and reaches saturation at B = 0.02 T. The energy effects in the crystals and solutions have been estimated.     

氯化钾水溶液微观结构的分子动力学模拟研究

氯化钾水溶液不同于氯化钠的,其在低温下只能形成无水盐和冰.现有研究表明在氯化钠水溶液中不仅存在着水分子连续分布的区域与离子团簇,而且这二者的物质组成也与该溶液所形成晶体的分别对应.为了探寻其他溶液中是否存在此类对应关系,并考察溶液的微观结构,本文采用分子动力学方法对氯化钾水溶液进行了研究,表明了该溶液的一些性质.氯化钾水溶液中K⁺-K⁺和Cl^--Cl^-径向分布函数的特征具有一致性,峰的最大值所对应的位置都分别相同,明显不同于氯化钠水溶液的.系列时刻下瞬态图像内O到其最近离子距离中最大值的统计结果表明氯化钾水溶液中存在着一定大小的水分子连续分布的区域,其平均尺寸至少为2.26 nm;瞬态图像中K⁺与其最近邻Cl^-之间的距离主要分布在0.28 nm～0.38 nm之间,占比约为97.4%;溶液中存在着较大和较小两类离子团簇,较大团簇的平均尺寸为1.73nm,平均离子数是25.0,其内部的离子与周围离子之间具有与氯化钾晶体类似的结构;这些结果表明氯化钾水溶液中也...     

Effect of the valence state of ce ions on the phase stability and mechanical properties of the crystals of ZrO<Subscript>2</Subscript>-based solid solutions

The structure and mechanical properties of the crystals of solid solutions of zirconium dioxide, which are stabilized by yttrium and cerium oxides, have been studied. The electron paramagnetic resonance technique has been used to identify Ce³⁺ ions and to determine their relative concentration in the crystals. It is shown that the presence of Ce³⁺ ions in the crystals is the main factor responsible for their high fracture toughness. The annealings carried out during investigations, which lead to a decrease in the concentration of Ce³⁺ ions, show that a change in the valence state of cerium ions lowers the fracture toughness of the crystals.     

Microtopographical studies of prism faces of potassium dihydrogen phosphate crystals

Surface structures on prism faces of potassium dihydrogen phosphate crystals grown from aqueous solutions and also by gel method are described and illustrated. Density of growth centres increases as the supersaturation of the mother liquor is increased. Gel grown crystals predominantly show rectangular growth hillocks on their prism faces. In the needle shaped crystals further nucleation extends predominantly along theC axis than at right angles to it. Influence of misoriented guest microcrystals on the growth of the prism faces is described.     

EFFECT OF LIGHT-INDUCED SCATTERING ON DIFFRACTION EFFICIENCY IN PHOTOREFRACTIVE CRYSTALS

The coupled wave equations and their analytic solutions in photorefractive crystals are presented for the case of two-beam writing, while the light-induced scattering is considered, Using this result, the diffraction efficiency for each writing beam is discussed in doped KNSBN crystals with unidirectional fan, which is explained theoretically and verified exper-imentally.     

AFM observation of a retgersite crystal surface growing in a water-ethanol solution

In situ investigation of the growth and dissolution of retgersite crystals α-NiSO₄ · 6H₂O in water-ethanol solutions (10–50 wt % of ethanol) was made by atomic force microscopy (AFM). The habit of crystals grown in aqueous and water-ethanol solutions, as well as the Raman scattering spectra, were identical. It is shown that the typical peak of sulphate ions at 981 cm⁻¹ does not change after the addition of ethanol. Absorption spectra of aqueous and water-ethanol solutions also have similar characteristic features. AFM images of hillocks on the (001) face of retgersite crystals were obtained directly in the process of their growth. Using a series of distorted AFM images obtained in situ, a geometrical calculation scheme is given, which allows one to recover the real direction of the growth steps. The kinetic coefficient of growth steps in aqueous and water-ethanol solutions of retgersite is estimated.     

On the luminescent properties of ZnS phosphors prepared at room temperature

We prepared ZnS phosphors and crystals without any firing at room temperature and atmospheric pressure directly from solutions of Zn-salts.The luminescent properties of the ZnS powders prepared by us are quite different from those previously described in the literature. Similarly, we also obtained from solutions ZnS crystals 100–200 in size.The authors wish to express their thanks to Dr. P. Gado for the X-ray measurements and helpful discussions.     

Crystal growth and phase transitions of solid solutions in [N(CH3)4]2MX4 isomorph class

Abstract

Homogeneous single crystals of tetramethylammonium tetrahalogenometallate solid solutions have been grown: a temperature difference growth method with thermally enforced convection was used during the material transport from an equilibrated feed material to the growing crystals. The smallest crystals were mostly studied by differential scanning calorimetry and X-ray crystallography. Some bigger crystals were available for dielectric measurements and Raman scattering. The temperature-concentration phase diagrams of solid solutions look like the temperature-pressure phase diagrams of pure tetramethylammonium salts. The progressive substitution seems equivalent to a change of the pressure, and is understood as a distortion of the metal-halide tetrahedron and a change of interactions with the first, second and third neighbours. The structure instabilities seem to have their origin within the b?c layers, and the increase of pressure (or equivalent concentration) should correspond to a hardening of the Layer-Shift Mode.     

Multilayer composite epitaxial CuCo single crystals

The ion-plasma spraying method was used to synthesize new phases of metastable atomic-ordered layered CuCo single crystals and single crystals of Cu_cCo_1?c solid solutions via epitaxial layer-by-layer crystallization, and some of their physical properties were studied.     

Kinetics of supersaturation decay in the crystallization of lysozyme

The molecular architecture of proteins can be determined by analysing the X-ray diffraction patterns of their crystals. The technology of X-ray crystallography has reached the point, however, where the determination of the structure of a given crystal is controlled by the limited availability of the crystals themselves. Proteins can often be crystallized from pH buffered aqueous solutions of strong electrolytes. When dissolved protein in solution is more stable than crystalline protein, the appearance of crystals can be said to be under thermodynamic control. If, on the other hand, the crystals are more stable than the dissolved protein, and still crystals are slow to appear, the crystallization can be said to be under kinetic control. Using dilatometry, we have followed the rate of decay of the protein supersaturation in crystallizing solutions of chicken egg-white lysozyme under conditions of kinetic control. We have found that the rate of decay of the supersaturation is first order in the supersaturation and that the rate constant is independent of the initial protein concentration, but increases with increasing pH, decreasing temperature, and with increasing concentrations of sodium chloride and buffer salt. We correlate these observed trends in the rate constant with related trends in the solubility and surface charge density of the crystals. We conclude that the rate constant for supersaturation decay is inversely proportional to the protein solubility.     

Structural physical regularities of the mechanism and kinetics of the formation of piezoelectric and ferroelectric crystals from a liquid phase

The specific features of the kinetics of formation of noncentrosymmetric crystals from electrolyte solutions are investigated for approximately 50 salts of M-N electrolytes. The “solubility product-limiting solution supercooling” set {SP-ΔT _m } for noncentrosymmetric crystals is separated into nine characteristic taxons in which the regularities of formation and growth of crystals are revealed and compared. It is demonstrated that the minimum supercoolings ΔT _m are observed for solutions of crystals with weak “acentric” properties. Higher supercoolings ΔT _m are observed for solutions of noncentrosymmetric crystals that belong to potential ferroelastics and exhibit pronounced acentric properties. The proposed taxonomy of electrolytes makes it possible to predict the conditions for the growth of perfect crystals for fundamental and applied physics.     

Structural and physical aspects of the formation of salt crystals from solutions

The peculiarities of the crystallization of about 100 solutions of different salts have been experimentally studied. A correlation is established between the maximum attainable supercooling temperature of the solution and the structure of the crystals formed. It is found that the highest supercoolings are characteristic of solutions of acentric crystals.     

On the question of Bi(III) complexes in NaCl

The absorption of trivalent bismuth in solutions of sodium chloride of different concentrations was studied. The absorption bands were ascribed to complexes of bismuth with chlorine. The agreement between absorption bands in NaCl and KCl crystals doped with bismuth and in sufficiently concentrated solutions shows that bismuth in these crystals forms an octahedral complex with six neighbouring chlorine ions.     

Effect of Co2+ on the growth,optical properties and laser damage threshold of potential nonlinear optical l-alanine single crystal

Good transparent bulk single crystals of pure l-alanine (LA) and cobalt doped LA crystals have been synthesized and successfully grown by slow-cooling method from their aqueous solutions. The concentration of metal dopants in the mother solution with 0.5 mol% for cobalt was carried out individually and crystals were obtained with well defined morphology. The as grown metal doped and pure single crystals were characterized by single crystal XRD studies which confirm that the incorporation of metallic dopants has not changed the basic structure of the parent crystal. The absorption of these crystals was analyzed and the result confirms that they possess low absorption in the range 230–1100 nm. Fourier transform infrared (FTIR) spectroscopy was carried out to investigate the molecular vibrations of these crystals and to confirm the incorporation of the dopants. The thermal properties have been studied by TGA/DTA curves. The EDAX measurement and surface morphology were studied for pure and metal doped LA crystals. The second harmonic generation (SHG) signals were observed using Nd: YAG laser with fundamental wavelength of 1064 nm in pure and metal doped crystals. The laser damage threshold was measured for pure and metal doped LA crystals and also tested by using a Q-switched Nd: YAG laser showed enhanced LDT value for metal (Co²⁺) doped LA crystal compared to pure LA crystal due to the metallic substitutions thus proving their useful candidature for nonlinear optical applications.     

Diffuse Reflectance Spectra of Some Nd3+ Complexes: Bonding

The absorption spectra of Na³⁺ complexes have been a subject of several recent investigations.^1–7 In the absorption spectra of solutions, the solvent effect makes it difficult to study the energy levels of the complexes. This difficulty can be overcome by studying the absorption spectra of single crystals or diffuse reflectance spectra of powders. Since the complexes under study do not form good single crystals, it was thought worthwhile to study their diffuse reflectance spectra, which have not been studied so far. The present communication reports a comparative study of bonding in six complexes inferred from their diffuse reflectance spectra.     

Solid solutions of paradichlorobenzene in paradibromobenzene with vacancies present in their structure

The results of polarization studies of the low-frequency optical Raman spectra of solid solutions of paradibromobenzene with p-dichlorobenzene (10% paradichlorobenzene) are reported. The spectra of lattice vibrations of the mixed crystals are calculated, and it is shown that vacancies can be present in their structure, in agreement with the experimental spectra. The existence of vacancies is manifested by the appearance of secondary lines in the low-frequency spectrum, in the vicinity of 70 cm⁻¹. The intensities of the lines are related to the number of vacancies. The diffusion activation energies in mixed crystals of paradibromobenzene with paradichlorobenzene with vacancies present in their structure are calculated at different temperatures on the basis of the method of atom-atom potentials. It is shown that the activation energy in these mixed crystals is not as dependent on the temperature variation and the crystallographic direction as in crystals of the constituent components. Fiz. Tverd. Tela (St. Petersburg) 39, 1564–1566 (September 1997)     

Parameters and properties of crystals of ionic compounds obtained by centrifugal separation of supersaturated aqueous solutions

The change in the chemical composition, structural parameters, and properties of Ba(NO₃)₂, PbCl₂, and KI crystals and the binary alkali-halide systems LiCl-KCl (eutectic) and LiCl-NaCl and KCl-KI (solid solutions) after centrifugal separation under acceleration (1.3, 6.2, 11.8)×10³ g is investigated. The composition variation was monitored by the methods of chemical gravimetric and titration analyses, as well as of flame-photometric and spectrophotometric analyses. Acceleration causes a change in the chemical composition, lattice parameter, refractive index, and microhardness in all systems as compared to the initial values. It is found that centrifugation affects the systems with different masses of cations more strongly than the systems with different masses of anions. A criterion of the ratio of the masses of ions (cations and anions) rat i/i is proposed for predicting the effect of centrifugation on the change in the chemical composition and properties of compounds and their systems (a larger value of this ratio leads to a stronger variation of the composition and properties). The crystals of all compounds and solid solutions display an increase in microinclusions (visible only in transmitted light) upon an increase in the acceleration. The lattice parameters and microhardness measured in KCl and KBr crystals four years after their fabrication by using centrifugal separation indicate a considerable return to their initial values.     

Intensity of the Mössbauer effect in crystals with vacancies and in solid solutions for the case of nonlocalized vibrations

The phonon spectra obtained in [2, 3] are employed to calculate the intensity of the Mössbauer line for crystals with vacancies and for solid solutions on the supposition that localized vibrations are absent and that the vacancy and impurity-atom concentrations are small. A method of calculating concentrations at low and high temperatures is proposed which is suitable for crystals with vacancies and for solutions of isotopes.     

Hydrodynamically induced crystallization of polymers from solution. VI. Amylose

A study has been made of the crystallization of amylose from stirred solutions. It was found that a highly turbulent flow can induce fibrillar crystallization in a 5% solution of amylose in 1 N KOH and in 35% chloral hydrate. Furthermore it was observed that these fibrillar crystals were insoluble in the original solution after crystallization.

Electron microscopic investigations revealed the presence of long fibrils, sometimes aggregated to larger units. Some fibers displayed transverse striations resembling the well-known shish-kebab structures. Treatment of the fibrillar crystals with iodine yielded the well-known blue coloring characteristic for amylose. However, in the electron microscope it was seen that only discrete portions of the fibers were stained.

Stirring of aqueous n-butanol solutions of amylose resulted in the formation of small rodlike fibrils in addition to lath-shaped single crystals to which a large number of tentacles were attached.

Rectangular-shaped crystals, grown in quiescent solutions, were deformed in a narrow gap couette instrument into long irregular fibers.