Growth of Yb-doped Y2O3, Sc2O3, and Lu2O3 single crystals by the micro-pulling-down technique and their optical and scintillation characterization

In this report, growth of Yb-doped sesqui-oxide crystals of Y₂O₃, Sc₂O₃, and Lu₂O₃ by the micro-pulling-down technique and their scintillation performance are discussed. Growth of these crystals is difficult mostly as a result of their extremely high melting point of around 2400 °C. Nevertheless, appropriate design of the thermal zone and careful control of the growth parameters allowed fabrication of these crystals of reasonable quality. Based on the results of measurements of emission spectra under α-ray excitation and pulse height spectra under α-ray and γ-ray excitations, scintillation characteristics of above crystals including emission wavelength and light yields under α-ray and γ-ray excitations were examined. Additionally, decay kinetics of these materials under α-ray excitation were evaluated.     

Crystal Growth of Lanthanum Beryllium Hexaaluminate LaBeAl11O19 and Fields of Crystallization in the System La2O3–BeO–Al2O3

The fields of crystallization in the system La₂O₃–BeO–Al₂O₃ are investigated. Single crystals of LaBeAl₁₁O₁₉ were grown by the Czochralski technique.     

Growth of Tetragonal Hausmannites MnxFe3−xO4 from Bi2O3-V2O5 Fluxes

The growing of tetragonal single crystals of Mn_xFe_3−xO₄ (x = 3.0 and 2.93) with hausmannite type structure is reported. Samples with x = 2.69 were no more monocrystalline due to the cubic-tetragonal transformation. Crystals were grown at temperatures from 1150 to 950°C from Bi₂O₃ + 10 wt.% V₂O₅ melts. The largest crystals reached nearly 10 mm in length and weights till to 0.5 g.     

Real Structure of LiB3O5 (LBO) Crystals Grown in Li2O‐B2O3‐MoO3 System

The liquidus surface structure and field of LiB₃O₅ (LBO) primary crystallization have been revealed in Li₂O‐B₂O₃ ‐MoO₃ ternary system. The optimization of charge composition and growth conditions results in large volume optical quality LBO single crystals yielding. Crystallographic properties and real defect structure of grown LBO single crystals have been investigated by X‐ray powder diffraction method and X‐ray reflection topography. The volume of the crystals is partly free of any structural imperfections.     

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.     

Luminescence effects accompanying Ba(BrO3)2 ⋅ H2O crystallization from solution

Kinetics of the Ba(Br₂O₃)₂ ? H₂O precipitation from aqueous solution and the accompanying luminescence effects are studied. Specific features of appearance of luminescence during grinding of Ba(Br₂O₃)₂ ? H₂O crystals are also examined. The origin of luminescence effects is interpreted as the result of electric discharge accompanying cracking of crystals during their growth or grinding.     

Flux crystallization of Pb(Mg1/3Nb2/3)O3 single crystals by the Czochralski method

Single crystals of lead magnesium niobate have been grown by flux crystallization using a modified Czochralski method. The crystals grown are free of pyrochlore impurity and have sizes of (15–28) × (20–30) × 20 mm³. The region of congruent melting of solution is determined. The PbO-B₂O₃ and PbO-B₂O₃-KBO₂ systems are chosen to be solvents.     

A new nonlinear optical crystal: Bi2O2(OH)(NO3)

The nonlinear optical (NLO) properties of Bi₂O₂(OH)(NO₃) crystals have been reported for the first time. Bi₂O₂(OH)(NO₃) crystals with dimensions of 1.3×1.2×0.1 mm³ have been grown by hydrothermal method, and the crystals characterized by X‐ray powder diffraction (XRD), SEM and IR. The measured second harmonic generation (SHG) effect of Bi₂O₂(OH)(NO₃) was about 7 times that of KDP. The mechanism responsible for the large SHG of Bi₂O₂(OH)(NO₃) was explained according to its structure. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Chemical Processes in Al2O3-Mo and Al2O3-W systems in a weakly reducing atmosphere

Al₂O₃-Mo and Al₂O₃-W systems in a controlled Ar(95%) + H₂(5%) atmosphere at T = 2400 K and P = 1 bar have been calculated by the Monte Carlo method. It is established that the presence of hydrogen in these systems leads to the occurrence of OH, H₂O₂, HO₂, H₂O, AlOH, AlOOH, AlH, AlH₂, and AlH₃ components in the gas phase; aluminum hydrides are formed only through the interaction of hydrogen with melt evaporation products. The presence of reducing medium leads to a decrease in the free oxygen concentration by one to two orders of magnitude, which is expected to improve the quality of sapphire crystals.     

Second harmonic generation properties of Ca3(O3C3N3)2 ‐Sr3(O3C3N3)2 solid solutions

Solid solutions of the second harmonic generation (SHG) materials Ca₃(O₃C₃N₃)₂ (CCY) and Sr₃(O₃C₃N₃)₂ (SCY) were prepared via exothermic solid state metathesis reactions from appropriate amounts of the corresponding metal chlorides and potassium cyanate at 525 °C. The change in SHG intensity caused by the successive cation substitution is reported. Differential thermal analyses are used to explore the SCY–K(OCN) phase diagram as a medium for the growth of SCY crystals.     

Structural properties of Cr2O3–Fe2O3–P2O5 glasses,Part I

The structural properties of xCr₂O₃–(40 − x)Fe₂O₃–60P₂O₅, 0 ⩽ x ⩽ 10 (mol%) glasses have been investigated by Raman and Mössbauer spectroscopies, X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The Raman spectra show that the addition of up to 5.3 mol% Cr₂O₃ does not produce any changes in the glass structure, which consists predominantly of pyrophosphate, Q¹, units. This is in accordance with O/P ≈ 3.5 for these glasses. The increase in glass density and T_g that occurs with increasing Cr₂O₃ suggests the strengthening of glass network. The Mössbauer spectra indicate that the Fe²⁺/Fe_tot ratio increases from 0.13 to 0.28 with increasing Cr₂O₃ content up to 5.3 mol%, which can be related to an increase in the melting temperature from 1423 to 1473 K. After annealing, the 10Cr₂O₃–30Fe₂O₃–60P₂O₅ (mol%) sample was partially crystallized and contained crystalline β-CrPO₄ and Fe₃(P₂O₇)₂. The SEM and AFM micrographs of the partially crystallized sample revealed randomly distributed crystals embedded in a homogeneous glass matrix. EDS analysis indicated that the glass matrix was rich in Fe₂O₃ (39.6 mol%) and P₂O₅ (54.9 mol%), but contained only 5.5 mol% of Cr₂O₃. These results suggest that the maximum solubility of chromium in these iron phosphate melts is 5.5 mol% Cr₂O₃.     

Various Growth Shapes of Na2S2O3 5H2O Crystals

The relation between the growth shapes and supersaturations and/or supercoolings was investigated in the Na₂S₂O₃ 5H₂O crystals: (i) The growth shapes changed from a hexagonal prismatic crystal, aggregate of platy crystals and to a spherulite with an increase of supersaturations and/or supercooloings. (ii) The deposition rate suddenly increased at a certain supersaturation and/or supercooling, where the growth shape changed from the hexagonal prism to the aggregate of platy crystals. (iii) The deposition rates of spherulites become higher with increasing the solute concentrations. (iv) The formation process of the spherulites were in situ observed by the Schlieren and/or Mach‐zehnder interferometer methods.     

Crystallization of KNbO3 in a B2O3 glass network

The ferroelectric material potassium niobate (KNbO₃) has a large number of exceptional electronic and optical properties with important technological applications. Due to the high preparation difficulties and costs of the single crystals, a considerable interest in the preparation of glass-ceramics with the KNbO₃ crystal phase exists. In this work we present the preparation of a glass, with the composition 40B₂O₃–40K₂O–20Nb₂O₅ (% mole), through the melt-quenching method and glass-ceramics obtained by controlled heat-treatments. The samples structure was analyzed using X-ray power diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. KNbO₃ crystals were detected in the glass sample treated at 500 °C. For treatments at temperatures above 500 °C, other niobium-based crystal phases are present. The behavior of the heat-treatment temperature parameter, in the glass and glass ceramic structure, is discussed.     

Sythesis and Characterization of Li3B5O8(OH)2 Crystals

Li₃B₅O₈(OH)₂ crystals were obtained in the system Li₂O B₂O₃ H₂O under hydrothermal conditions at fairly lower PT conditions. The crystals obtained were characterized through various techniques: XRD, wet chemical analysis and the measurement of ionic conductivity.     

Refinement of the crystal structure of Na2Ti3O7

The crystals of Na₂Ti₃O₇ were obtained by crystallization from flux. The structure of the compound was refined from X-ray diffraction data collected on a four-circle diffractometer (2θ/θ scanning technique, λMoK _α radiation, graphite monochromator, θ_max = 40°). The crystals are monoclinic a = 9.133(2) Å, b = 3.806(1) Å, c = 8.566(2) Å, β = 101.57(3)°, sp. gr. P2₁/m, Z = 2, ρ_calcd = 3.435 g/cm³, R = 0.035, 1241 reflections with I ≥ 2σ(I). The geometric characteristics of the Ti-polyhedra are analyzed as to their positions in the trioctahedral ribbon. The polymorphism of the {Ti₃O₇}^2? anionic radical in the structures of Na₂Ti₃O₇ and PbTi₃O₇ is described. The topology and dimensionality of the { Ti₃O₇}^2? anionic radical are demonstrated to depend on the type of the large cations located at the lattice points of the hexagonal close packing characteristic of both structures.     

Synthesis and crystal growth of sillenite phases in the Bi2O3 ‐ TiO2 ‐ Nb2O5 system

The synthesis of Bi₂O₃‐Nb₂O₅ sillenite phase (BNbO) and the solubility of this phase with Bi₁₂TiO₂₀ was investigated by solid‐state reaction synthesis and niobium doped Bi₁₂TiO₂₀ (BTO:Nb) crystals were grown by the Top Seeded Solution Growth (TSSG) technique. The structures of polycrystalline compounds were checked by X‐ray powder diffraction method at room temperature. The correct composition of the sillenite phase stabilized with niobium was determined as Bi₁₂[Nb_0.17Bi_0.83]O_19.7 (BNbO) with unit cell parameter a = 10.261(2) Å. The system BTO‐BNbO is poorly soluble, but niobium doped BTO crystals were grown from the liquid composition 10Bi₂O₃ : xTiO₂ : (1‐x)/2 Nb₂O₅, with x = 0.95 and 0.90. A niobium concentration limit in the liquid phase is established in order to grow BTO:Nb with good crystalline quality. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of composition on ionic transport in SiO2–B2O3–Na2O glasses

Ionic diffusion was investigated in the SiO₂–B₂O₃–Na₂O glass system over a wide composition range by impedance spectroscopy measurements. The Na⁺ cation transport mechanism was described by an interstitial pair migration model based on Frenkel defects in ionic crystals. The activation energy of the static electrical conductivity is shown to be correlated with the boron coordination number in these glasses. Published ¹¹B NMR results were used to calculate the activation energies of sodium cations acting as charge compensators for the [BO_4/2]⁻ tetrahedron and of sodium cations bonded to non-bridging oxygen atoms. These values are in agreement with the activation energies of the Na₂O–B₂O₃ and Na₂O–SiO₂ binary systems, respectively.     

Mass spectrometric analysis of gaseous crystallization medium,growing, and some properties of α-Al2 18O3 crystals

Some gas phase processes during the vacuum vertical directed crystallization of α-Al₂ ¹⁸O₃ are studied in this paper. An effect of these processes on the H, C, N concentrations in the crystals is discussed. The detected pulsations of partial H₂ and C¹⁸O pressures are a result of bubble destruction at the melt-gas interface. The C¹⁸O bubbles are formed because of chemical interaction between the melt and carbon-containing phases of container material. Besides the container wall, the H₂ bubbles can be generated also at the crystallization front supersaturated by H₂. The perfect α-Al₂O₃ and α-Al₂ ¹⁸O₃ crystals grown under the same conditions have noticeable differences of their density, microhardness and lattice parameters. This is explained by an isotopic substitution effect.     

Growth and properties of Lu3Al5O12-RE3+ single crystals

Optically transparent garnet single crystals were grown from Lu₃Al₅O₁₂ melts containing different RE³⁺ ions. The distribution coefficient of Nd³⁺ ions is found to be a function of the growth rate. Lu₂O₃–Al₂O₃ system studies have been partially carried out. Measurements of the lattice data, absorption spectra and comparison with some properties of Y₃Al₅O₁₂ single crystals have also been made.     

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.