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 of single crystals of NaH2PO4 (NaDP), NaH2PO4 · H2O (NaDP · H2O), and NaH2PO4 · 2H2O (NaDP · 2H2O) sodium dihydrogenphosphate based on the analysis of the Na2O-P2O5-H2O phase diagram

The crystallization conditions for the NaH₂PO₄, NaH₂PO₄ · H₂O, and NaH₂PO₄ · 2H₂O solid phases have been established from the analysis of the phase diagram of solubility of the ternary Na₂O-P₂O₅-H₂O system in the temperature range from 0 to 100°C. Based on these data, the methods for growing sodium dihydrogenphosphate single crystals of the above compositions are developed. The initial components for preparing mother solutions were H₃PO₄ and NaOH solutions taken in certain weight ratios. For the first time, NaDP, NaDP · H₂O, and NaDP · 2H₂O single crystals were grown on a seed by the method of temperature decrease. The habits of the NaDP and NaDP · H₂O single crystals are determined. __________ Translated from Kristallografiya, Vol. 47, No. 5, 2002, pp. 937–944. Original Russian Text Copyright ? 2002 by Soboleva, Voloshin.     

Phase equilibria in the Ba2Na3[B3O6]2F-BaF2 system

The phase equilibria in the Ba₂Na₃[B₃O₆]₂F-BaF₂ section, which belongs to the ternary mutual Ba, Na//BO₂,F system, have been studied by the methods of solid-phase synthesis, visual polythermal analysis, and differential-thermal analyses. It is shown that this section can be used to grow bulk Ba₂Na₃[B₃O₆]₂F crystals.     

Crystal growth and characterization of K2B4O11H8

Single crystals of K₂B₄O₁₁H₈, a non-centrosymmetric borate material, have been prepared by slow evaporation of water solution at room temperature. The crystals were colorless and transparent with smooth faces. The single-crystal X-ray diffraction analysis showed that K₂B₄O₁₁H₈ crystallized in the orthorhombic space group P2₁2₁2₁ with a=6.8556(6) Å, b=11.7787(12) Å, c=12.8949(14) Å, Z=4, R₁=0.0188, and wR₂=0.0464. The powder X-ray diffractometry (PXRD), infrared spectrum, transmittance spectrum, TG–DTA curves and second harmonic generation properties of title compound have been determined.     

Crystal structure and phase transitions in the new crystals of [(CH3)2NH2]2CuCl4[(CH3)2NH2]Cl

Crystals grown from a solution of dimethylammonium and copper chlorides are studied using electron paramagnetic resonance (EPR) and X-ray diffraction. The dielectric properties of the crystals grown are measured. It is established that the crystals have the composition [(CH₃)₂NH₂]₂CuCl₄[(CH₃)₂NH₂]Cl and, in phase I at room temperature, are described by the orthorhombic space group Pna2₁ with the unit cell parameters a = 11.338 Å, b = 9.981 Å, and c = 15.675 Å. At temperatures of 279 K and 253 K, the crystals undergo jumpwise phase transitions into the incommensurate modulated ferroelectric phase II and commensurate modulated phase III, respectively. __________ Translated from Kristallografiya, Vol. 49, No. 1, 2004, pp. 92–100. Original Russian Text Copyright ? 2004 by Kirpichnikova, Pietraszko, Bednarski, Waplak, Sheleg. Dedicated to the 80th Birthday of L.A. Shuvalov     

Growth of congruently melting Ca0.59Sr0.41F2 crystals and study of their properties

Homogeneous crystals of Ca_0.59Sr_0.41F₂ alloy (sp. gr., Fm $ \bar 3 $ \bar 3 m, a = 0.56057 nm), corresponding to the point of minimum in the melting curve in the CaF₂-SrF₂ phase diagram, have been grown by the vertical Bridgman method. The optical, mechanical, electrical, and thermophysical properties of Ca_0.59Sr_0.41F₂ and MF₂ crystals (M = Ca, Sr) have been studied and comparatively analyzed. Ca_0.59Sr_0.41F₂ crystals are transparent in the range of 0.133–11.5 μm, have refractive index n _D = 1.436, microhardness H _μ = 2.63 ± 0.10 GPa, ion conductivity σ = 5 × 10⁻⁵ S/cm at 825 K, and thermal conductivity k = 4.0 W m⁻¹ K⁻¹ at 300 K. It is shown that the optical properties of Ca_0.59Sr_0.41F₂ crystals are intermediate between those of CaF₂ and SrF₂, whereas their mechanical and electrical characteristics are better than the latter compounds.     

Large-size and high-quality Zn2TiO4 single crystal grown by the optical floating zone method

Crack-free and transparent Zn₂TiO₄ single crystals of 4–6 mm in diameter and 30 mm in length have been grown by the optical floating zone method. The powder X-ray diffraction (XRD) results show that the as-grown crystals have the spinel-type Zn₂TiO₄ structure. XRD² measurements on Zn₂TiO₄ wafers cut perpendicular to the growth direction display only one peak at 42.7°, which indicates that the Zn₂TiO₄ single crystals grow along the 〈4 0 0〉 direction (a-axis). The formation of bubble inclusions was effectively suppressed by lowering rotation rate. Transmission polarized-light microscopy results showed that as-grown crystals were free of low angle grain boundaries.     

Solubility phase diagrams of Me 2SO4-NiSO4-H2O systems and the growth of Me 2Ni(SO4)2 · n H2O crystals [ Me = Na, Rb, Cs; n = 4, 6]

On the basis of the physicochemical analysis of the solubility phase diagrams for the Me ₂SO₄-NiSO₄-H₂O ternary systems (Me = Na, Rb, or Cs), the optimum concentration and temperature conditions for the crystallization of the Me ₂Ni(SO₄)₂ · nH₂O solid phases were found. Techniques for growth of single crystals of these binary salts have been developed. Such techniques allow application of mother liquors containing hydrates or anhydrous sulfates of Na, Rb, Cs, and Ni as raw materials. Na₂Ni(SO₄)₂ · 4H₂O, Rb₂Ni(SO₄)₂ · 6H₂O, and Cs₂Ni(SO₄)₂ · 6H₂O single crystals (28–34) × (8–13) × (5–10) mm³ in size have been grown from aqueous solutions in the dynamic regime. Original Russian Text ? L.V. Soboleva, 2007, published in Kristallografiya, 2007, Vol. 52, No. 6, pp. 1141–1144.     

Growth of (CH3)2NH2CuCl3 single crystals using evaporation method with different temperatures and solvents

The bulk single crystals of low-dimensional magnet (CH₃)₂NH₂CuCl₃ (DMACuCl₃ or MCCL) are grown by a slow evaporation method with different kinds of solvents, different degrees of super-saturation of solution and different temperatures of solution, respectively. Among three kinds of solvent, methanol, alcohol and water, alcohol is found to be the best one for growing MCCL crystals because of its structural similarity to the raw materials and suitable evaporation rate. The best growth temperature is in the vicinity of 35 °C. The problem of the crystals deliquescing in air has been solved through recrystallization process. The crystals are characterized by means of X-ray diffraction, specific heat and magnetic susceptibility.     

Zur Züchtung von CaF2-UND CaF2(U)-einkristallen aus der dampfphase

Monocrystals of pure and uranium-doped CaF₂ have been grown from the vapour phase in graphite crucibles using a vertical moving gradient method with seed-selection. The growth technique and the properties of the vapour phase grown crystals are described. Evaporation temperatures: 1450–1550 °C, δT≌ 65 °C, growth temperatures: ca. 1300–1400 °C. Dopant: UF₄. Size of the crystals up to 18 mm in diameter and 50 mm in length. In accordance to the low colour center formation by X-raying the pure CaF₂ crystals contain only a small number of lattice defects. The uranium content and distribution in the doped crystals depends strongly on vaporization temperature and inner shape of the crucibles, the valence of the uranium in the CaF₂(U) crystals is mainly determined by the fluorine vapour pressure in the growth system. Tetravalent U can be incorporated in the presence of PbF₂ and trivalent U under high vacuum.     

Bulk crystallisation of (00l) oriented fresnoite Sr2TiSi2O8 in glass-ceramics of the Sr-Ti-Si-K-B-O system

This paper shows that glass-ceramics containing highly surface and bulk preferentially oriented fresnoite Sr₂TiSi₂O₈ crystals can be synthesised by a simple isothermal heat treatment of suitable glass compositions in the Sr-Ti-Si-K-B-O system. For all tested compositions, crystallisation starts from the free surfaces of the specimens and propagates to bulk with time. If most of these compositions lead to (00l) preferential orientation at the specimens' surfaces, bulk crystal texture is very composition dependent. The effects of variation in K₂O and B₂O₃ contents on the crystallisation have been studied. It is shown that low K₂O and high B₂O₃ contents are required to keep the (00l) orientation from the surface into the bulk. This result seems to be explained by the viscosities of the initial and residual glasses at the temperature of crystallisation: a low viscosity leads to a fine and homogeneous microstructure with small and strongly (00l) bulk oriented crystals.     

Single crystals growth and absorption spectra of Cr-doped Al2−xInx(WO4)3 solid solutions

The growth conditions of pure and Cr³⁺-doped Al_2−xIn_x(WO₄)₃ single crystals, using top-seeded solution growth (TSSG) technique, have been studied. A series of experiments have been performed at different In concentrations, x=0.0, 0.3, 0.6 and 1.0, as well as at different concentrations of Cr³⁺ (0.0, 0.1, 0.2, 0.5 and 1.0) in at% with respect to the initial total concentration of Al and In in the starting solutions. The basic parameters of the crystal growth are varied over a wide range: seed orientation, speed of rotation, axial and radial temperature differences in the solution and the solution cooling rate. The investigated relations between the basic defects in the crystals and these parameters result in determination of the optimal conditions for growth of defect-free crystals. Distribution coefficients of Al, In and Cr have been determined, so the growth of crystals with given compositions is possible. Values of Dq/B (crystal field strength) for the various crystal compositions are calculated from the optical absorption spectra. The calculated values show that the discussed solid solutions have weak crystal field and are suitable for media with broadband emission spectra.     

Phase separation and crystallization in the system SiO2-Al2O3-P2O5-B2O3-Na2O glasses

The phase separation and crystallization behavior in the system (80 − X)SiO₂ · X(Al₂O₃ + P₂O₅) · 5B₂O₃ · 15Na₂O (mol%) glasses was investigated. Glasses with X = 20 and 30 phase separated into two phases, one of which is rich in Al₂O₃-P₂O₅-SiO₂ and forms a continuous phase. Glasses containing a larger amount of Al₂O₃-P₂O₅ (X = 40 and 50) readily crystallize and precipitates tridymite type AlPO₄ crystals. It is estimated that the phase separation occurs forming continuous Al₂O₃-P₂O₅-SiO₂ phase at first, and then tridymite type AlPO₄ crystals precipitate and grow in this phase. Highly transparent glass-ceramics comparable to glass can be successfully obtained by controlling heat treatment precisely. The crystal size and percent crystallinity of these transparent glass-ceramics are 20-30 nm and about 50%, respectively.     

Vitrification and crystallization in the system of K2O-B2O3-TiO2

The vitrification and crystallization behavior of melts produced at 1400 °C in the ternary system of K₂O-B₂O₃-TiO₂ is investigated. It is shown that there are two fields of compositions (indicated in mol%) which allow obtaining the glass-ceramic materials with continuous glassy matrix after the cooling of molten compositions. In the first field [TiO₂] = 25-57, [K₂O] = 30-50 and [B₂O₃] = 0-25, the glass-ceramics consisted of the potassium-titanium-borate glassy phase and different crystalline potassium titanates (K₄Ti₃O₈, K₂Ti₂O₅, K₂Ti₄O₉, K₂Ti₆O₁₃). The ratio of TiO₂:K₂O in the obtained titanates increases with [TiO₂] and [B₂O₃]. In the second field, [TiO₂] = 7-37, [K₂O] = 0-25 and [B₂O₃] = 52-93, the obtained glass-ceramics consisted of a similar vitreous phase, as mentioned above, and TiO₂ crystals. During the cooling of the melts, short whiskers-like crystals of anatase formed in the compositions with relatively low [TiO₂] and relatively high [K₂O], whereas long fiber-shaped crystals of rutile appeared with the compositions characterized with relatively high [TiO₂] and relatively low [K₂O]. The possible application of the obtained glass-ceramic materials as a source of fibrous TiO₂, for composite reinforcement, and as solid lubricants is discussed.     

Direct observations of pseudo-binary NdBa2Cu3Ox–Ba3Cu10O13 phase diagram and NdBa2Cu3Ox crystallization under reduced oxygen atmosphere

The pseudo-binary NdBa₂Cu₃O_x–Ba₃Cu₁₀O₁₃ phase diagrams and the crystallization of NdBa₂Cu₃O_x have been in situ observed using high-temperature optical microscope under three different oxygen atmospheres namely 1%, 0.1% and 0.0097% oxygen in argon. It has been observed that the liquidus line becomes narrower both in composition and temperature with decreasing oxygen pressure. This result suggested that under reduced oxygen atmosphere, the NdBa₂Cu₃O_x crystals could only be grown from a peritectic melt consisting of Nd₄Ba₂Cu₂O₁₀ and liquid. The crystallization temperature of NdBa₂Cu₃O_x was found to decrease logarithmically with decreasing oxygen content in the atmosphere.     

Floating-zone growth of large high-quality CoAl2O4 single crystals

We report the first successful floating-zone growth of high-quality CoAl₂O₄ single crystals with volume up to 1 cm³ free from inclusions and sub-grains. The neutron rocking curves of the CoAl₂O₄ crystal have the width of about 0.30 degree proving the excellent quality of the grown samples. X-ray synchrotron experiments show that crystals have spinel structure with the lattice constant a₀=8.09853(1) Å. Magnetization measurements give the effective magnetic moment μ_eff=4.63 μ_B per Co⁺² ion in a good agreement with previous measurements on ceramic samples.     

Phase equilibria and growth of β-BaB2O4 crystals in the BaB2O4-Ba2Na3[B3O6]2F system

A complex investigation of the BaB₂O₄-Ba₂Na₃[B₃O₆]₂F cut, which belongs to the ternary mutual Ba, Na//BO₂, F (BaB₂O₄-(NaBO₂)₂-(NaF)₂-BaF2) system, has been performed. The cut is quasibinary, with the following eutectics coordinates: 810 ± 5°C, 85 mol % Ba₂Na₃[B₃O₆]₂F, 15 mol % BaB₂O₄. It is shown that this system can be used to grow bulk β-BaB₂O₄ crystals.     

Flux growth and morphology analysis of Na3VO2B6O11 crystals

Colorless and transparent Na₃VO₂B₆O₁₁ (NVB) crystal has been grown by the top seeded solution growth method using NaVO₃ as the flux at cooling rates of 0.8–1.5 °C/day, in the temperature range 610–650 °C. A well-developed morphology of the crystals was observed and analyzed. The grown crystals were characterized by powder X-ray diffraction (PXRD), infrared spectroscopy and second harmonic generation (SHG) test.     

Crystal growth of ferroelastic K2Cd2(SO4)3 and the K2SO4-CdSO4 phase diagram

Crystals of congruently melting K₂Cd₂(SO₄)₃ (having the langbeinite structure with a ferroelastic transition temperature of 156°C) were grown by the Bridgman and Czochralski techniques. The former yielded colorless crystals when using oxygen under pressure; the latter yielded tan crystals of slightly smaller unit cell volume and are assumed to be oxygen deficient. The ferroelastic transition was studied by thermal expansion measurements. Reexamination of the phase diagram showed the existence of a previously unreported phase K₆Cd(SO₄)₄ which is stable only between 520°C and the melting point of about 890°C.     

Growth kinetics and micromorphology of NH4Cl:Mn2+ crystals formed in the NH4Cl-MnCl2-H2O-CONH3 system

The growth kinetics and elementary growth processes on the surface of NH₄Cl:Mn²⁺ heterogeneous crystals formed in the NH₄Cl-MnCl₂-H₂O-CONH₃ system are experimentally studied. It is found that a change in the composition of complexes in an NH₄Cl crystal from Mn(NH₄)₂Cl₄ · 2H₂O to MnCl₂ · 2CONH₃ leads to the occurrence of a local maximum in the kinetic curve and a change in the shape of dislocation growth centers from flat to conical. The growth kinetics of {100} faces of heterogeneous NH₄Cl:Mn²⁺ crystals is described within the Bliznakov model using the Fowler-Guggenheim adsorption isotherm, which takes into account the lateral interaction of adsorbed particles.