Crystals of rare-earth-ferrous borates

Crystals of rare-earth-ferrous borates (structure of carbonate mineral huntite, space group R 32) were obtained from the solution-melt with the Bi₂O₃-B₂O₃ base. It was established by the methods of X-ray structural and chemical analyses that large amounts of Bi from the solution became part of the crystals affecting their solubility, morphology and hardness. Solubility curves for YFe-, NdFe-, and ErFe-borates in the 3 Bi₂O₃ 5 B₂O₃ melt were plotted. Refinement of crystalline structure of NdFe-borate showed that bismuth takes up place of rare-earth ion in the crystal lattice. Parameters of unit cells, density and refractive indexes of the obtained crystals were measured.     

Single‐crystal growth and characterization of mullite‐type orthorhombic Bi2M4O9 (M = Al3+, Ga3+, Fe3+)

Pure and homogeneous single crystals of orthorhombic mullite‐type Bi₂M₄O₉ (M = Al³⁺, Ga³⁺, Fe³⁺), and a mixed Bi₂Fe_1.7Ga_2.3O₉ crystal from an equimolar Ga/Fe composition were grown by the top seeded solution growth (TSSG) method. All these compounds melt incongruently in the range of about 800 and 1100 °C. In case of bismuth gallate and ferrate inclusion‐free crystals with dimensions up to several cubic centimeters can be grown. Limited solubility in Bi₂O₃ and the high steepness of the liquidus curve are the reasons for getting only small imperfect bismuth aluminate crystals. In contrast to ceramic materials preparation reported in literature, divalent calcium and strontium could not be incorporated into the mullite‐type structure during the melt growth process. Several fundamental physical properties like heat capacity, thermal expansion, heat conductivity, elastic constants, high‐pressure behavior and oxygen diffusivity were determined by different research groups using single‐crystalline samples from the as‐grown materials. Furthermore, the refractive indices of Bi₂Ga₄O₉ were measured in the range of 0.430 and 0.700 μm. Such as many other bismuth containing compounds the refractive indices of Bi₂Ga₄O₉ are larger than 2, and Bi₂Ga₄O₉ is an optic biaxial positive crystal. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal Growth of Boron Sillenite Bi24B2O39

The Sillenite type Bi₂₄B₂O₃₉ is an incongruently melting compound at T_p = 650 °C. Single crystals have been grown from non-stoichiometric melts as well as from high temperature solutions by the Czochralski method and by a top seeded solution growth technique (TSSG), respectively. The main difficulty in the crystal growth of Bi₂₄B₂O₃₉ arises from the very small field of crystallization in the binary system Bi₂O₃–B₂O₃. Further problems are caused by the nearly simultaneous formation of the 2:1 compound Bi₄B²O₉ and the 12:1 compound Bi₂₄B₂O₃₉. Therefore, a precise thermal reinvestigation of the phase diagram was carried out using DTA-technique on the Bi₂O₃-rich side. Additionally, crystal growth runs have been started in the ternary system Bi₂O₃–B₂O₃–Li₂O in order to extend the crystallization field. Homogeneous melts were more difficult to prepare because of the high density difference between Bi₂O₃ (∂ = 9.3 g/cm³) and B₂O₃ (∂ = 2.46 g/cm³). The homogeneity of the melts were improved, using Bi₂O₃ and synthesized Bi₄B₂O₉ (∂ = 8.25 g/cm³) as starting materials. As a result of this procedure, small crystals of Bi₂₄B₂O₃₉ were grown from these starting materials and the lattice parameter were determined.     

Single crystal preparation of MnxCr3–xO4 by flux method

Mn_xCr_{3 x}O₄ was prepared by the flux method. Melts of PbO PbF₂, Bi₂O₃ B₂O₃, B₂O₃, Na₂B₄O₇, and Na₂W₂O₇ Na₂WO₄ were used. The best results could be yielded with the PbO PbF₂ flux, from which crystals with 2–4 mm in thickness were grown. The Bi₂O₃ B₂O₃ flux produced crystals with 1–2 mm in thickness. The spinell structure of the chromite was proved by X-ray investigation.     

Structural investigation of bismuth borate glasses and crystalline phases

Glasses of the system: xBi₂O₃-(100−x)B₂O₃ (x = 20 to 66 mol%) were prepared and characterized by density, DSC, UV-visible absorption and ¹¹B MAS-NMR spectroscopy. Glass molar volume increases while the glass transition temperature decreases with Bi₂O₃ concentration. Densities of some bismuth borate glasses are found to be greater or very close to those of single crystal phases with equal composition. B¹¹ MAS-NMR studies determined that the fraction of tetrahedrally coordinated borons (N₄) is maximum at 42 mol% of Bi₂O₃ and that there is a local maxima in N₄ at Bi₂O₃ concentration of 50 mol%. Glasses containing Bi₂O₃ concentration of 33 mol% and higher show an unusual, intense absorption band just below the optical band gap. Two crystalline phases: Bi₃B₅O₁₂ and Bi₄B₂O₉ were prepared by devitrification of glasses and characterized by X-ray diffraction, FTIR and ¹¹B MAS-NMR studies. Both crystalline phases contained significantly lower N₄ than glasses with equal composition.     

Infrared and Raman spectroscopy of mullite‐type Bi2Ga4O9

Mullite‐type Bi₂Ga₄O₉ single‐crystals were grown by the top‐seeded solution growth (TSSG) method and investigated by vibrational spectroscopy. Polarised IR specular reflectance and attenuated total reflectance (ATR) spectra, as well as polarised micro‐Raman spectra were acquired at room temperature. Powder IR spectra of sol‐gel‐derived samples were also recorded. Using model calculations and comparison to other mullite‐type compounds, bands at ∼ 850 – 400 cm^‐1 could be assigned to stretching and bending vibrations of the structural GaO₄ and GaO₆ units. Low‐energetic modes were attributed to motions involving Bi atoms. The IR spectra of Bi₂Ga₄O₉ display close similarities to those of the mullite‐type alkali gallates (9Ga₂O₃ · Rb₂O), while their differences to those of mullite sensu stricto (3Al₂O₃ · 2SiO₂ and 2Al₂O₃ · SiO₂, repectively) are assigned to Si‐O stretching vibrations of the corresponding tetrahedral units. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Infrared Optical Characterization of Thermally Oxidized CuInSe2 Single Crystals

Infrared reflectivity spectra of thermally oxidized CuInSe₂ single crystals are measured at room temperature in the wavenumber range from 180 to 4000 cm⁻¹. A Kramers-Kronig analysis of the spectra reveals seven vibrational modes with frequencies which agree with mode frequencies in In₂O₃. No vibrational modes due to Cu–O and Se–O bonds could be observed. The results obtained are compared with previous studies of oxidized CuInSe₂ crystals.     

Recrystallization of natural chrysoberyl in multicomponent melts

Chrysoberyl and alexandrite crystals have been grown from solutions in melts based on the Li₂CO₃-MoO₃, Bi₂O₃-MoO₃, PbO-V₂O₅, Na₂B₄O₇, and K₂MoO₄-MoO₃ systems using natural alexandrite and chrysoberyl debris as the initial BeAl₂O₄ compound. An analysis of the morphology and homogeneity of the crystals grown has revealed the Bi₂O₃-MoO₃ solvent to be the most appropriate. The optimal color characteristics (??quality?? of alexandrite effect) manifest themselves when adding about 5 mol % Cr₂O₃. The largest crystals (up to 10 mm in size) were obtained from a solution in melt based on PbO-V₂O₅ at a ratio of the crystal-forming component to the solvent of 9: 91 wt %; These characteristics, along with a relatively low operating temperature (970°C), give grounds to consider this type of solvent promising.     

Growth and structure of α-Bi2B8O15 crystals

α-Bi₂B₈O₁₅ crystals (5-to 7-mm-thick, 2.7 × 2.7 cm² in cross section) have been grown by the Czochralski method from a melt of stoichiometric (Bi₂O₃: B₂O₃ = 20: 80) and nonstoichiometric (Bi₂O₃: B₂O₃ = 21.9: 78.1) compositions. It is established that there is a solid-solution range from 78.1 to 84.7 mol % B₂O₃ for α-Bi₂B₈O₁₅. The structure of a Bi₂(B₈O₁₅)(Bi₂O₃)_0.06 crystal, which was grown from a melt of nonstoichiometric composition and is an interstitial solid solution, has been refined (sp. gr. P2₁).     

X-ray Photoelectron Spectroscopic Studies of Sellinite and Eulytite BGO and BSO Crystals

Single crystals of Bi₁₂GeO₂₀, Bi₁₂SiO₂₀, Bi₄Ge₃O₁₂, and Bi₄Si₃O₁₂ are grown by Floating zone and Czochralski techniques. The X-ray photoelectron spectroscopic (XPS) studies have been carried out on BSO and BGO crystals. XPS is employed to characterise the surface quality and bulk nature of the crystals. The surface contamination on both types of crystals are identified. In addition to the contamination, some amount of Bi atoms are observed with Bi ions on sellinite. It is demonstrated that the eulytite crystals are chemically more robust to degradation than the sellinite crystals. The predominant covalent and ionic character of Bi₄Ge₃O₁₂ and Bi₄Si₃O₁₂ respectively is explained from their oxygen 1s core level spectra.     

Influence of the melting conditions of heavy metal oxide glasses containing bismuth oxide on their optical absorption

Glasses of the systems Bi₂O₃-SiO₂, Bi₂O₃-PbO-Ga₂O₃, Bi₂O₃-PbO-Ga₂O₃-GeO₂ and Bi₂O₃-GeO₂-Li₂O have been prepared and the interaction of their melts with crucibles of different materials has been analytically determined. Silica and porcelain crucibles were very strongly corroded and the glass composition was noticeably altered. Instead platinum crucibles are not affected if the Bi₂O₃ content is not too high. The color of the glasses changes in all cases from pale yellow to deep brown when the melting temperature reaches approximately 1000 °C. The higher the temperature and the Bi₂O₃ content the darker the brown color, independently of the nature of the employed crucible. The addition of oxidizing ions (Sb⁵⁺, As⁵⁺ or Ce⁴⁺) to the glass batch prevents darkening. Nanoparticles of elementary bismuth Bi⁰ are observed by transmission electron microscopy in the glasses melted above 1000 °C. The partial thermoreduction of the Bi₂O₃ during the heating of the glass melt is proposed as the mechanism responsible for the observed darkening.     

Structure of Gd<Subscript>0.95</Subscript>Bi<Subscript>0.05</Subscript>Fe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> single crystals at 293 and 90 K

The structure of GdFe₃(BO₃)₄ single crystals has been studied by X-ray diffraction at 293 and 90 K. The crystals are grown from a flux in the Bi₂Mo₃O₁₂–B₂O₃–Li₂MoO₄–Gd₂O₃–Fe₂O₃ system. The results of chemical analysis and structural study show that these crystals contain bismuth as an impurity. It is found that bismuth atoms are located at gadolinium sites in the structure. A decrease in the temperature is accompanied by a lowering of the symmetry from sp. gr. R32 (at 293 K) to sp. gr. P3₁21 (at 90 K). The presence of two types of iron chains with different geometries at 90 K promotes a change in the magnetic properties of these crystals with a decrease in the temperature.     

High-Temperature Crystallization,Composition, Structure,and Certain Properties of Rare-Earth Gallium Borates

Solution-melts based on PbF₂—B₂O₃ and Bi₂O₃—B₂O₃ were used in studying the stability regions and for growth, by way of spontaneous crystallization, of crystals up to 3 mm in size of twelve compounds having the general formula RGa₃(BO₃)₄. All of these compounds are isostructural with carbonate mineral huntite. Their composition is highly dependent on that of the crystallization medium. The facing of the crystals is characterized by a small number of simple forms {101 1}, {112 0}, {21 1 0}, and less frequently {022 1}, {0112}, {404 1}. The examined parameters include the IR spectra, luminescence spectra, heat of formation from oxides, harness (6 to 8 units on the Mohs scale) and others.     

New Ln[B6O9(OH)3] borates (Ln = Sm-Lu): Structure, properties, and structural relation to cationic Li4[B7O12]Cl conductors (Li-Boracites)

Crystals of new rare earth borates of the composition Ln[B₆O₉ (OH)₃] (Ln = Sm-Lu), sp. gr. R3c are synthesized under hydrothermal conditions. Their crystal structures are determined on single crystals with Ln = Ho, Gd without preliminary determination of their chemical formulas. The polar anionic framework of the crystals consists of BO₃ triangles and BO₄ tetrahedra and has wide channels along the threefold axis of the structure, which are similar to the channels along the a, b, and c axes in cubic Li₄[B₇O₁₂]Cl boracite with Li conductivity. Rare earth atoms are arranged in the structure over the cubic F pseudolattice, whereas the analogous positions in Li boracites are filled with Cl anions. The squared optical nonlinearity of the new crystals is comparable with the nonlinearity of quartz, whereas the electrical conductivity in borates at 300°C exceeds 10⁻⁶ S/cm. __________ Translated from Kristallografiya, Vol. 49, No. 4, 2004, pp. 681–691. Original Russian Text Copyright ? 2004 by Belokoneva, Ivanova, Stefanovich, Dimitrova, Kurazhkovskaya.     

Improved Single Crystal Growth of the Boron Sillenite “Bi24B2O39” and Investigation of the Crystal Structure

The boron sillenite, up to now known as the 12:1 compound Bi₂₄B₂O₃₉ in the system Bi₂O₃ – B₂O₃ andcrystallizing in the space group I23, melts incongruently at 655 °C only about 25 K above the eutectic tie line and corresponding to a steep liquidus line. Single crystals with dimensions larger then 1 cm ³ have been successfully grown in [100], [110], and [111] direction by an improved Top Seeded Solution Growth (TSSG) technique equipped with crucible weighing, accelerated crystal rotation technique and air‐cooled pulling rod. The structure of the boron sillenite was analyzed by X‐ray diffraction method, which was possible due to the high crystalline quality achieved. A defect‐free sublattice corresponding to a Bi‐O framework is isostructural with all sillenites, but a 2 Å environment around the origin is occupied by different cations with different population coefficients. The best calculation results in the formula Bi_24.5BO_38.25 which is more Bi‐rich than the 12:1 assumption.     

Growth,structure, and some transport properties of topological insulators based on bismuth chalcogenide single crystals

Single crystals of topological insulators—bismuth chalcogenides Bi₂Te₃, Bi_{2 ? x} Sn _x Te₃, Bi₂Se₃, and Bi_{2 ? x} Cu _x Se₃ with different charge-carrier densities—are grown by the modified Bridgman method. Their composition and structure are investigated and temperature dependences of the electric resistance and magnetic field dependences of the Hall voltage are obtained.     

Calculation of thermodynamic parameters of melts from experimentally determined liquidus‐curves

Thermodynamic parameters of melts (ΔH_S, A₀, A₁) in the system Anorthite‐Diopside and Bi₂O₃‐Bi₄B₂O₉ have been calculated by a rigorous application of solution thermodynamics. The data are internally consistent and yield values of ΔH_S for Anorthite = 133 kJ/mole, Diopside = 81 kJ/mole, Bi₂O₃ = 19 kJ/mole and Bi₄B₂O₉ = 39 kJ/mole. The activity of Anorthite and Diopside in an anorhtitic melt deviates negative from ideality, whereas a diopsidic melt behaves almost ideal. In a “Bi₂O₃” melt the activity of the Bi₂O₃ component is strongly positive, that of Bi₄B₂O₉ is strongly negative. The opposite is observed for the “Bi₄B₂O₉” melt. All calculated liquidi except the Bi₄B₂O₉ liquidus closely match the experimental ones. In contrast to the experimental liquidus the calculated Bi₄B₂O₉ liquidus has an inflection point. The crest of the metastable spinode (solvus) for a “Bi₂O₃” melt is close to the liquidus indicating melt separation at undercooling. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural investigations of copper doped B2O3-Bi2O3 glasses with high bismuth oxide content

Raman and infrared spectroscopy have been employed to investigate the 99.5%[xB₂O₃(1−x)Bi₂O₃]0.5%CuO glasses with different Bi/B nominal ratios (0.07?x?0.625) in order to obtain information about the competitive role of B₂O₃ and Bi₂O₃ in the formation of the glass network. The glass samples have been prepared by melting at 1100 °C and rapidly cooling at room temperature. In order to relax the structure, to improve the local order and to develop crystalline phases the glass samples were kept at 575 °C for 10 h. The influence of both Bi₂O₃ and CuO on the vitreous B₂O₃ network as well as the local order changes around bismuth and boron atoms in as prepared and heat treated samples was studied. Structural modifications occurring in heat treated samples compared to the untreated glasses have been observed.     

Structure of phases of the sillenite family in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-V<Subscript>2</Subscript>O<Subscript>5</Subscript> system

X-ray diffraction studies of sillenite Bi₂₄V₂O₄₀ single crystals grown by the hydrothermal method are performed for a separate crystal and powdered crystals. It is found that the composition of the two specimens is described by the (Bi_{24 − x} ▭ _x )[Bi _y ³⁺V_1−y ⁵⁺]₂ O₄₀ general formula with completely populated oxygen sites but differs in the content of vacancies at the bismuth site (this was established for the first time) and the Bi: V ratio at the tetrahedral site. The structural models of all the vanadium-containing sillenites reported in the literature are considered, and the possibility that Bi atoms are located at the centers of BiO₄ tetrahedra is established.     

Effect of Li2O on the heterogeneous structure of equi-molar lead borate glasses

Different glass samples in the Li₂O, PbO and B₂O₃ system have been prepared by melt quenching method. These glasses were classified in two groups such as 0.5 B₂O₃, (0.5 ? x) PbO, xLi₂O and (0.5 + y) B₂O₃; (0.25 ? y)PbO; 0.25Li₂O. The IR spectra almost show broad bands in the frequency range (800–1050) cm^?1 and (1100–1500) cm^?1, together with different weak bands over the range of investigation (2400–3000) cm^?1. The deconvolution analyses of these IR spectra reveals presence of multi structure arrangements from BO₄ and BO₃ groups, such as penta, tri, and diborates grouping together with meta; ortho borates as well as PbO_n groups. Partial replacement of PbO by Li₂O causes decrease in microhardness, a change which is attributed to the decrease in the concentration of ortho borate groups as is it revealed from the bands area analysis. The IR analysis shows also that the total concentration of (meta + ortho) borates is nearly constant while their individual concentrations is proportional depending on the relative concentration of PbO and Li₂O.