Growth of Er2(SO4)3 ⋅ 8H2O crystals and study of their structure and properties

New crystals of the composition Er₂(SO₄)₃ ? 8H₂O have been synthesized by the method similar to that used for synthesis of (CH₃)₂NH₂Al(SO₄)₂ ? 6H₂O. The synthesized crystals were studied by the X-ray diffraction method. The crystals are monoclinic C2/c) and contain no (CH₃)₂NH₂ ions. It is established that, contrary to DMAAS crystals, Er₂(SO₄)₃ ? 8H₂O crystals undergo no phase transitions and possess neither ferroelectric nor ferroelastic properties.     

The Improvement of Superconductivity in PbxBi2-xSr2CaCu2Oy

In this paper we present the results of recent studies on the improvement of superconductivity in Pb_xBi_2-xSr₂CaCu₂O_y single crystals by preventing impurities incorporation, employing ZrO₂ crucible for crystal growth and post annealing the as-grown crystals in vacuum or argon. It is realized that the superconductivity of as-grown crystals is improved.     

Characterization of pure and doped potassium hydrogen tartrate single crystals grown in silica gel

Growth of pure‐, sodium‐ and lithium‐ doped potassium hydrogen tartrate single crystals by gel technique is reported. Growth conditions conducive for the growth of single crystals are worked out. The crystals are characterized by using powder XRD, SEM, FTIR, AES, EDAX, CH analysis and thermoanalytical techniques. The stoichiometric composition for the grown crystals are established as KHC₄H₄O₆.H₂O, (K)_0.98(Na)_0.02.H₂O and (K)_0.94(Li)_0.06HC₄H₄O₆.H₂O. Doping of sodium and lithium in the pure potassium hydrogen tartrate single crystals is found to influence the size, perfection, morphology, crystal structure and the thermal stability of crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of single crystal growth of GaPO4 by the flux method

GaPO₄ crystals have been grown by a spontaneous nucleation method and the top-seeded solution growth method using three different solvents, 3MoO₃-Li₂O, 3MoO₃-K₂O and 2KPO₃-5MoO₃-3LiF. All of the as-grown crystals were characterized by means of X-ray powder diffraction. The results show that all the crystals were well crystallized and belong to the point group 32, and 2KPO₃-5MoO₃-3LiF flux is the best for nucleation and growth of transparent GaPO₄ crystals. The infrared spectrum of GaPO₄ single crystal obtained by the flux method shows that there is no incorporation of OH groups during the crystallization, which is beneficial for high temperature piezoelectric applications.     

Investigations on the crystallization of larger NaA and NaX zeolite crystals in the presence of triethanolamine (I). The influence of Na2O and SiO2 content

Sodium silicate-aluminate aqueous systems with various contents of Na₂O and SiO₂ containing triethanolamine were crystallized. Optimum Na₂O and SiO₂ contents have been observed to give NaA and NaX zeolite crystals with dimensions up to 80 μm. For NaA crystals the values are: ∼ 3.5 mass% Na₂O, ∼ 1.65 mass% SiO₂; for NaX crystals ∼ 2.5 mass% Na₂O, ∼ 1.5 mass% SiO₂. – The effect of other additives on crystal size is proved. – The results are discussed in terms of nucleation and growth, reaction rate, and supersaturation. Supposition are made to gain larger crystals by maintaining the excess of solute over a longer period of time.     

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 of hollow Bi2Se2S crystals from vapour

Hollow crystals of Bi₂Se₂S have been grown from vapour. Crystals show open lateral surface and the length of the crystals is 6 to 7 mm. An explanation is given for the growth mechanism of the hollow crystals.     

Growth of PbWO4: Me F2( Me F2 = PbF2, BaF2) single crystals and their properties

PbF₂-and BaF₂-doped PbWO₄ crystals have been grown by the Czochralski method. The scintillation characteristics of the grown crystals have been determined. It is shown that introduction of BaF₂ leads to an increase in the light yield of PbWO₄ crystals by 20%, while PbWO₄:PbF₂ crystals demonstrate a significant increase in radiation hardness.     

Growth and luminescence of CsBr:Cu crystals

Special features of the incorporation of a copper impurity into CsBr crystals are studied for different types of impurities (metallic copper, CuO, and CuBr₂) and crystal-growth techniques (the Bridgman method or the method of isothermal evaporation from solution). The optical characteristics of these crystals (absorption, photoluminescence, and photostimulated-luminescence spectra) are investigated. The copper impurity is shown to enter CsBr:Cu_met crystals in the monovalent state Cu⁺ and CsBr:CuO and CsBr:CuBr₂ crystals in the divalent state Cu²⁺. It is found that the CsBr crystals doped with Cu⁺ and Cu²⁺ ions exhibit intense photostimulated luminescence and can be used as storage phosphors for visualization of X-ray images.     

Structure and properties of single crystals of tin-doped potassium titanyl phosphate

Single crystals with the compositions KTi_0.47Sn_0.53OPO₄ and KTi_0.25Sn_0.75OPO₄ were grown by spontaneous crystallization from flux in the K₂O-TiO₂-SnO₂-P₂O₅ quaternary system, and their structures were established from precision X-ray diffraction data. The incorporation of tin into the crystals lowers the asymmetry of cation positions in the (Ti,Sn)O₆ octahedra. The addition of even a small amount (x < 0.4) of tin to the K(Ti_{1 ? x} Sn_x)OPO₄ crystals causes fast symmetrization of the octahedra. The process slows down with an increase in the tin content until the attainment of the composition KSnOPO₄ and localization of tin in the centers of octahedra. It is these structural features that are responsible for a decrease in the optical nonlinearity of the crystals and in the intensity of second harmonic generation by laser radiation in these crystals.     

Production of high purity TeO2 single crystals for the study of neutrinoless double beta decay

High purity TeO₂ crystals are produced to be used for the search for the neutrinoless double beta decay of ¹³⁰Te. Dedicated production lines for raw material synthesis, crystal growth, and surface processing were built compliant with radio-purity constraints specific to rare event physics experiments. High sensitivity measurements of radio-isotope concentrations in raw materials, reactants, consumables, ancillaries, and intermediary products used for TeO₂ crystals production are reported. Indications are given on the crystals perfection and how it is achieved and maintained in a large scale production process. Production and certification protocols are presented and resulting ready-to-use TeO₂ crystals are described.     

Microhardness studies on as‐grown (111) faces of some alkaline earth nitrates

Single crystals of Sr(NO₃)₂, Ba(NO₃)₂ and Pb(NO₃)₂ are grown from their aqueous solutions at a constant temperature of 35 °C by slow evaporation technique. Crystals of size 8 to 10 mm along one edge are obtained in a period of 10 days. Chemical etching technique has been employed to study the dislocations in these crystals. The dislocations are randomly distributed and the dislocation density is about 10⁴ to 10⁵ /cm². Microhardness studies are made on as–grown (111) faces of these crystals upto a load of 100 g. The hardness of the crystals increases with an increase in load and thereafter it becomes independent of the applied load. These results are discussed on the basis of reverse indentation size effect. Meyer index number n for these crystals is estimated at both low and high load regions. An analysis of hardness data of these crystals as well as some other cubic crystals like alums and alkali halates are discussed using Gilman–Chin parameter H_v/C₄₄, where H_v is the microhardness and C₄₄ is the shear constant. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of lithium triborate (LiB3O5) single crystals in the Li2O-B2O3-MoO3 system

Solubility curves are plotted and optimal solvents for growing lithium triborate (LiB₃O₅) single crystals are determined. The crystallization range of this compound in the Li₂O-B₂O₃-MoO₃ system is refined. The molybdenum content in the crystals grown is analyzed.     

Hydrothermal Synthesis and Characterization of VSZ-3 Zeolite Crystals

Zeolite crystals (named here VSZ-3) synthesized at 350°C by hydrothermal method are illustrated and described. These crystals are shown to be analcime type zeolites. It is established that their size is the largest among the zeolite crystals ever reported, and are stable upto 1000°C. The VSZ-3 crystals are prismatic pyramidal and needle-like. They are characterized by X-rays, SEM, TGA, DTA and IR. Their chemical composition is shown to be 5.95 SiO₂ ṁ Al₂O₃ ṁ 0.91 Na₂O ṁ 0.17 H₂O. Mechanism of growth of these crystals is explained.     

The Influence of High Temperature Predeformation on Ductility of LiF and BaF2 Single Crystals

The effect of high temperature predeformation on deformation characteristics of ductile LiF and brittle BaF₂ crystals was investigated. The same predeformation, as has been shown previously, leads to the increasing of the limited plastic deformation of MgO crystals by one order of magnitude. It was found that in both investigated crystals, as in the case of MgO crystals, at the test temperature T₂ ≅ 0.1 T_m limited plastic deformation before fracture obviously increases if the specimen was prestrained up to ε_p ≦ 1% at T₁ = 0.5 T_m. This increase is as higher as the plasticity of crystal is lower. In BaF₂ crystals it reaches a factor of 20 and more. The effect is connected with the creation of mobile dislocations during the high temperature predeformation and dislocaton sources for subsequent deformation at lower temperatures and with the homogeneity of the process of plastic deformation. These conditions prevent the appearance of dangerous places in which the fracture can begin.     

Growth of MgF2 optical crystals and their ionic conductivity in the as-grown state and after partial pyrohydrolysis

MgF₂ single crystals have been grown from melt by the Bridgman technique in a fluorinating atmosphere. To control the presence of oxygen impurity, it was first suggested to measure the ionic conductivity in MgF₂ crystals by impedance spectroscopy. The characteristics of ionic conductivity of “as grown” (i.e., without thermal treatment) crystals and crystals obtained by commercial vacuum technology practically coincide: the volume conductivity σ_v = 1.4 × 10^?7 S/cm at 773 K and the ion-transport activation energy E _a = 1.40 ± 0.05 eV. Annealing MgF₂ crystals during electrophysical studies upon heating from 293 to 823 K in vacuum (residual pressure ～1 Pa) for 4 h led to their partial pyrohydrolisis. The influence of this thermal treatment of MgF₂ crystals on their optical transmission is studied in the wavelength range of 115–300 nm.     

Growth of lanthanum heptamolybdate crystals by gel technique

The growth of single crystals of lanthanum heptamolybdate is achieved by allowing controlled diffusion of La ions through silica gel using the system La(NO₃)₃ MoO₃ NH₄OH HNO₃–Na₂SiO₃. The reaction mechanism leading to the growth is reported. Mechanism of crystallization of La heptamolybdate is discussed. Formation of Liesegang rings consisting of La heptamolybdate crystals in the system is reported. It is observed that concentration programming and seeded growth enhances the size of crystals. The crystals grown in the system are single crystal platelets exhibiting squarish or octagonal facets. Some crystals exhibit a spherulitic morphology.     

Growth and study of PbFe1/2Ta1/2O3 single crystals

Single crystals of the composition PbFe_1/2Ta_1/2O₃ are grown by the method of mass crystallization from flux. It is established that, unlike the PbFe_1/2Ta_1/2O₃ ceramic, the synthesized single crystals possess pronounced relaxor properties: the maximum of the dielectric constant is diffuse and its temperature, T _m, increases by more than 70 K with an increase in the frequency from 10² to 10⁶ Hz. It is assumed that the unusual properties of the PbFe_1/2Ta_1/2O₃ crystals are caused by mesoscopically inhomogeneous compositional ordering and comparatively high conductivity providing favorable conditions for the appearance of the volume-charge and thermal electron polarization.     

Crystal and molecular structures of potassium cobalt hydrogen phthalate K2[Co(H2O)6](C8H5O4)4 ⋅ 4H2O and mechanism of Co2+ impurity trapping in KAP crystals

The single-crystal X-ray diffraction analysis of K₂[Co(H₂O)₆](C₈H₅O₄)₄ ? 4H₂O has been carried out. The K₂[Co(H₂O)₆](C₈H₅O₄)₄ ? 4H₂O single crystals are obtained in attempting to grow the KAP crystals with the maximum possible content of Co²⁺ impurity cations. The crystals are isostructural to the earlier-studied similar crystals with Ni(II). The structure is formed by double layers of biphthalate anions and the Co²⁺ and K⁺ cations in between. The Co²⁺ cations are coordinated only by water molecules, whereas the coordination of the K⁺ cations involves both the biphthalate anions and water molecules. A detailed crystal chemical analysis, together with the data on the growth kinetics of KAP crystals in the presence of Co²⁺ and the mass-spectrometric data obtained earlier for the KAP crystals, leads to the conclusion that the Co²⁺ impurity cations should be located in the form of the [Co(H₂O)₆]²⁺ cationic complexes in the interblock layers of the KAP crystals.