Morphology of BBO Crystals and their Inclusions

This paper reports on the morphology and inclusions in the low temperature phase barium metaborate BaB₂O₄(BBO) crystal grown by an improved flux pulling method. The morphology of ideal BBO crystals and the relationship between the faces and the growth rate are given. The result that BBO has the symmetry L₃3P and belongs to the space group C_3v−3m can therefore be concluded. It is found that the polarity of the BBO crystal along the Z (or c) axis has a visible influence on the morphology. The investigation of the inclusions in BBO crystals shows that these have a six-fold symmetry which corresponds to the extension of flute-like facets. It is also found that most of the inclusions have a regular geometric figure and can be regarded as the negative-crystal structure which is due to the internal growth mechanism.     

Specific features of the flux growth of bulk crystals of high-temperature modification of BaB2O4

High-quality single crystals of the high-temperature phase of barium metaborate (α-BaB₂O₄) up to 100–120 g in weight are grown from a flux in the ternary system BaO-B₂O₃-Na₂O. The growth temperature is below the α → β phase transition temperature. The conditions necessary for growing α-BaB₂O₄ crystals under metastable conditions are determined and the morphology and optical quality of the crystals grown are investigated.     

Growth and characterization of high purity single crystals of barium ferrite

High purity single crystals of barium ferrite have been grown with the use of a BaO flux. The detected residual impurities have a total concentration of 130 ppm (wt), of which 100ppm is due to platinum. While the crystals exhibit occassional inclusions of a barium rich phase, the predominant microstructural defects are voids, which exhibit two geometries; one spherical and one hexagonal. Magnetic and resistivity measurements have yielded values which are comparable to those reported in the literature. Room temperature effective linewidth measurements at 10 GHz indicate that eddy current losses are dominant for disk shaped samples thicker than ≈0.3 mm. Room temperature FMR linewidth measurementson a sample 0.04 mm thick exhibit a linear frequency response between 55 and 90 GHz, which is consistent with a Landau-Lifshitz damping mechanism.     

Growth of crystals of calcium sulphate in silica gel in presence of additive and their characterisation

Procedure for the growth of calcium sulphate dihydrate crystals in silica gel, in the presence of barium chloride as additive, is described. Optimum conditions for the growth of good quality crystals are worked out. The crystals are characterised by laser Raman spectroscopy, infrared spectroscopy, thermogravimetric analysis and Atomic absorption spectroscopy. It is shown that crystals in the presence of the additive have a greater degree of perfection than those without additive. Amount of water in the crystals is estimated as 20.97%. Presence of calcium and absence of barium in the crystals are indicated.     

Effect of external forces on the dielectric and pyroelectric properties of strontium-barium niobate crystals

It is shown that high-temperature annealing of strontium-barium niobate crystals increases the mobility of domain boundaries in these crystals. This effect manifests itself in a shift of the peak of the effective permittivity of annealed samples to weaker fields. It is ascertained that the polarization of strontium-barium niobate crystals caused by annealing results in their more homogeneous single-domain state. The effect of Ce and Cr impurities on the polarization state of the surface layers in strontium-barium niobate crystals is considered.     

Growth and etching of anhydrous diglycine sulfate single crystals

Single crystals of anhydrous diglycine sulfate are grown at constant temperature by evaporation method. The crystals are grown at various temperatures and their growth rate is determined. A chemical etchant for dislocation studies is reported. The perfection of the crystals grown at various temperatures has been studied using etching technique. It is found that the crystals contained inclusions of the mother liquid. The crystals grown below 28° are almost free of inclusions and the dislocation density is also low.     

Compositional mapping of GaSb wafers from as-grown crystals and after post-growth annealing treatments

Spatial compositional analysis has been carried out on single and polycrystal wafers of GaSb grown from stoichiometric and non-stoichiometric melts. In crystals grown from stoichiometric melt, the ratio of Ga to Sb is slightly more and remains uniform throughout. At the grain boundaries in polycrystals, the Sb content is more than in the other regions of the crystal. Crystals grown from either Ga- or Sb-rich melts exhibit inclusions of the excess component. Post-growth annealing treatments in vacuum and Ga-rich atmospheres have been performed. Heat treatments in vacuum atmosphere produce very little effect on the local composition of the crystal. On the other hand, localized crystallization at grain boundaries and inclusions takes place in the presence of excess gallium. It has been shown that annealing treatments in Ga ambient can produce defect-free wafers with extremely homogeneous composition. It is concluded that the excess Sb which is liberated from the crystal during growth resides at the grain boundaries and other extended defect centers. The vacant Sb sites are then responsible for the formation of the native acceptor centers like V_Ga and Ga_Sb.     

挥发物对BBO晶体的腐蚀研究

采用顶部籽晶法,以NaF为助熔剂生长非线性光学晶体材料β-BaB2O4(简称BBO)晶体.在生长过程中发现挥发物掉落在晶体表面并严重腐蚀晶体.通过X射线粉末衍射分析,发现挥发物的主要成分是NaF,它不仅腐蚀晶体表面,而且引起晶体内部包裹物的形成.X射线衍射分析和质谱分析表明包裹物的主要成分是BaB2O4,另有少量Na+存在.探讨了由挥发物引起晶体内部形成包裹物的机理.     

Growth of functional single crystals of complex compounds on the basis of the solubility phase diagrams of ternary systems

The validity of solubility phase diagrams of ternary systems for determining the optimal (concentration and temperature) dynamic growth conditions for single crystals of congruently and incongruently dissolving solid phases is shown. It is found that the optimal composition of the mother liquor for growing solid-phase single crystals corresponds to the solution in the solid-phase solubility curve that is located at the maximum distance from the points of invariant equilibria. More than 40 ternary systems have been used and more than 60 new and known large functional single crystals of stoichiometric composition and optical quality that belong to different chemical classes have been grown on their basis under dynamic conditions.     

Study of inclusions and growth bands in potassium bichromate crystals grown from aqueous solutions

The nature of inclusions and growth bands in potassium bichromate crystals obtained from aqueous solutions and their formation in relation to growth temperature and supersaturation are investigated. It is observed that impurities present in solution, fluctuations in growth temperature and high growth rates are responsible for their formation.     

Synthesis and magnetic properties of copper metaborate single crystals, CuB2O4

Large high-quality single crystals of copper metaborate are grown on the basis of the phase diagram of the ternary Li₂O-CuO-B₂O₃ system. Bright blue crystals with a volume of about 1 cm³ were grown by the method of spontaneous crystallization while slowly cooling the melt. The magnetic susceptibility and electron spin resonance were measured. It is shown that the effective magnetic moment of a Cu²⁺ ion is equal to 1.6 μ_B and the g-factor, to 2.170 and 2.133 for the magnetic field oriented parallel and perpendicular to the fourfold axis, respectively. At 21 and 10 K, sharp anomalies of magnetic susceptibility are observed.     

Contribution to High-temperature Modifications of the Anhydrous Alkaline Earth Metal Sulfates

Large synthetic crystals of alkaline earth metal fluorides, especially fluorite crystals, contain sometimes unknown small inclusions of hexagonal form. Samples of these crystals were investigated by microscope, X-ray, and microprobe analysis to identify the included small crystals. Optical behaviour of these inclusions, morphology, chemical composition, and the reaction with water allow their interpretation as high-temperature modifications of the anhydrous water soluble alkaline earth metal sulfates, partly transformed to the corresponding sulfides.     

Growth and analysis of barium-sodium niobate crystals

The conditions of growth, monodomenization, and detwinning are considered in order to obtain optically perfect barium–sodium niobate crystals (BSN). Optical homogeneity and that of chemical composition are investigated. It is shown that possible variations of composition in a crystal's volume are below 1%. Thermal E and optical E_g° widths of the forbidden zone are determined in the absorption spectra.     

X-Ray Topographic Investigation of Silicon Single Crystals Heavily Doped with Sb

Heavily Sb doped silicon crystals grown by Czochralski method were investigated using X-rays methods. It is shown that growth striation contrast is caused by inhomogeneous Sb distribution. While approaching the lower part of crystals their volume is being contaminated by dispersive particles of noncontrolled impurities that results in decrease of anomalously transmitted X-rays and weakening of the contrast in topographical growth striation image. In the canal connected with the facet effect crystal structure is less damaged by foreign inclusions.     

Epitaxial overgrowth of gold and silver on an electrically heterogeneous surface of NaCl crystals

Epitaxial overgrowth of gold and silver on the surface of NaCl crystals containing inclusions of the impurity PbCl₂ has been studied on an electromicroscopic scale. The inclusions are surrounded by a double electric layer, on the negatively charged surface of which oriented coalescence of silver primarily proceeds. It is shown that the electrical relief plays the decisive part in epitaxial overgrowth, under otherwise identical experimental conditions.     

Effect of In and Sb Vacancies on Temperature Dependence of InSb Lattice Parameter at High Temperatures

The temperature dependence of the thermal expansion coefficient for InSb has been determined in the range 25–515 °C by precision measurements of the lattice parameter of InSb single crystals. It is shown that beginning from 460 °C the temperature dependence of the lattice parameter for InSb single crystals grown from melts of different compositions is essentially affected by vacancies in the indium and antimony sublattices. The vacancy concentration and possible deviation of InSb from the stoichiometric composition are estimated from a relative decrease in the lattice parameter.     

Origin and relation of three kinds of scatter centers in KDP and DKDP crystals

The origin of three kinds of scatter centers in KDP and DKDP crystals and their relations were investigated. The results have shown that solid inclusions will form liquid and gas inclusions in KDP (DKDP) crystals. The effect of scatter centers on Laser Damage Threshold of the crystals is not same because their sizes are different. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dispersion of the polarization processes in Ca<Subscript>0.32</Subscript>Ba<Subscript>0.68</Subscript>Nb<Subscript>2</Subscript>O<Subscript>6</Subscript> crystals

The switching processes in calcium barium niobate crystals CaxBa_1–x Nb₂O₆ with x = 0.32 have been investigated. The dielectric hysteresis loops observed in the samples exposed to alternating fields of different frequencies and constant amplitude have been analyzed. It is shown that the loop formation is caused by the sample heating. The sample temperature increases due to the dielectric loss energy release only up to a certain frequency, above which complete switching becomes impossible.     

The mechanism of formation of light-scattering centers in sapphire crystals grown in gas atmospheres

The mechanism of the formation of light-scattering centers in sapphire crystals grown by horizontal directed crystallization in gas atmospheres reducing with respect to the Al₂O₃ melt was studied. The experimental regularities here significantly differ from those observed upon formation of other conventional defects in sapphire crystals (vacancy pores, gas bubbles, and so on). It is shown that the known formation mechanisms of macroscopic ≥1 mm) inclusions in crystals are not acceptable in this case. Using the model of bulk crystallization is proposed to describe the obtained regularities.     

Spontaneous crystallization of diamonds in the nickel-manganese system with admixtures of group IV elements

The regularities in the changes in the average size, yield, and impurity composition of diamond crystals synthesized in the nickel-manganese system with admixtures of group IV elements are established. It is found that the average size of crystals in a set increases with increasing Ti concentration. It is shown that the yield of the diamond phase is affected significantly by impurities and almost independent of the metallic melt composition.