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)     

Structural analysis of Na2OGa2O3SiO2 glasses by the X-ray diffraction method

The structure of Na₂OGa₂O₃SiO₂ glasses of four different compositions containing up to 45 mol. % Ga₂O₃ has been determined by the X-ray diffraction method. The radial distribution function D(r) obtained indicates that Ga³⁺ ions are in fourfold coordination and GaO₄ tetrahedra are formed in these glasses. The reduced intensity function S·i(S) and radial distribution function D(r) which were calculated based on a structural model for A-25, 0.25(Ga₂O₃)·0.75(Na₂O·2SiO₂)/3 glass agreed well with the observed ones.     

Glass formation and properties in the gallia-calcia system

The critical cooling rate for glass formation was measured for five compositions in the Ga₂O₃?CaO system and varied from a low of (315 ± 85) °C/s for a eutectic melt containing 37.5 mol.% Ga₂O₃ to a high of (840±60)°C/sec for a melt containing 52 mol.% Ga₂O₃. Selected properties of glasses containing from 37.5 to 62 mol.% Ga₂O₃ were measured. The density and refractive index, n_D, both increased with increasing Ga₂O₃ content, but the crysallization temperature and microhardness varied only slightly with Ga₂O₃ content. The IR spectra of these glasses suggest that both GaO₄ tetrahedra and GaO₆ octahedra are present.     

An X‐ray powder diffraction study of the microstructural evolution on heating 3:2 and 2:1 mullite single‐phase gels

Single‐phase gels with compositions 3Al₂O₃·2SiO₂ and 2Al₂O₃·SiO₂ were prepared by gelling mixtures of aluminium nitrate and tetraethylorthosilicate. Gels were fast heated at different temperatures between 900°C and 1600°C. The phase transformation and microstructural changes of both mullite precursor gels over the temperature range were followed by X‐ray powder diffraction (XRD), lattice parameter determination (LP), and scanning and transmission electron microscopies (SEM and TEM). The distribution of crystallite sizes and strains were determined by linewidth refinements of X‐ray diffraction patterns using the integral breadth method of Langford and the Warren‐Averbach analysis. XRD of both heated gels showed the formation of crystalline mullite single phase. Some amount of glassy phase coexisted with mullites at low temperatures, i. e. below 900°C. The compositional range of mullites formed on heating gels at temperatures between 900°C and 1600°C was dependent on the starting nominal composition of gels. SEM and TEM micrographs of both heated gels below 1200°C showed the formation of small, discrete, prismatic, well‐shaped nanocrystals in a very ordered arrangement. The size of these nanocrystals was dependant on the nominal composition of gels and increased on rising the heating temperature of gel precursors. The microstructural features obtained from linewidth refinement results of X‐ray diffraction patterns also allowed to suggest the formation of prismatic a little elongated nanocrystals at temperatures below 1200°C. Microstrain values were small and only displayed a relatively significant value for mullites processed at 900°C. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of oxide fibers by the internal crystallization method

A new approach is developed for growing relatively inexpensive single-crystal and eutectic oxide fibers suitable for the fabrication of high-temperature composite materials. Sapphire (Al₂O₃), YAG (Y₃Al₅O₁₂), mullite (3Al₂O₃ · 2SiO₂), YAP (YAlO₃), and eutectic (Al₂O₃-Y₃Al₅O₁₂, Al₂O₃-ZrO₂ (Y₂O₃), and Al₂O₃-Gd₂O₃) fibers are produced by the internal crystallization method, and their mechanical strength and micro-structures are studied.     

Effect of Al2O3 on the viscosity and structure of calcium silicate-based melts containing Na2O and CaF2

The effect of Al₂O₃ on viscosity in the calcium silicate melt-based system containing Na₂O and CaF₂ was investigated and correlated with the melt structure using FTIR (Fourier transform infrared) spectroscopy, XPS (X-ray photoelectron spectroscopy), and Raman spectroscopy. Substituting SiO₂ with Al₂O₃ modified the dominant silicate network into a highly structured alumino-silicate structure with the aluminate structure being particularly prevalent at 20 mass% of Al₂O₃ and higher. As the melts become increasingly polymerized with higher Al₂O₃ content, the fraction of symmetric Al–O⁰ stretching vibrations significantly increased and the viscosity increased. XPS showed a decrease in the amount of non-bridged oxygen (O^?) but an increase in bridged oxygen (O⁰) and free oxygen (O^2?) with higher Al₂O₃. Although changes in the structure and viscosity with higher CaO/(SiO₂ + Al₂O₃) were not significant, the symmetric Al–O⁰ stretching in the [AlO₄]^5?-tetrahedral units decreased. The apparent activation energy for viscous flow varied from 118 to 190 kJ/mol.     

On the Crystal Structure of Tribarium Gallate (Ba3Ga2O6)

Single crystals of tribarium gallate (Ba₃Ga₂O₆) have been synthesized from a melt with composition 70 mol.% BaO and 30 mol.% Ga₂O₃ in the temperature range between 1200 °C and 1400 °C. The compound adopts space group Pa with a = 16.746(9) Å and Z = 24 formula units per unit cell. The refinement of the atomic parameters resulted in a residual of R1 = 0.040 (wR2 = 0.102) for 1157 observed reflections (I>2 σ (I)). Ba₃Ga₂O₆ belongs to the group of cyclo‐gallates and is closely related to K₄SrGe₃O₉. Main building element are isolated, highly puckered, twelve‐membered rings build by [GaO₄]‐tetrahedra. Charge balance is achieved by incorporation of Ba ions in the voids between the rings. The coordination number of the alkaline earth atoms is six, eight and nine, respectively.     

Thermal properties and glass formation in the SiO2–B2O3–Bi2O3–ZnO quaternary system

Lead-free glasses in the SiO₂–B₂O₃–Bi₂O₃–ZnO quaternary system were studied. The glass formation region, as determined by XRD patterns of bulk samples, was limited to glasses having more than 40 mol% of the glass-forming oxides SiO₂ and B₂O₃. Crystalline phases of Zn₂SiO₄ (willemite) were detected in compositions of 30SiO₂ · 10B₂O₃ · 20Bi₂O₃ · 40ZnO and 20SiO₂ · 10B₂O₃ · 25Bi₂O₃ · 45ZnO. Glass transition temperatures (T_g), dilatometric softening points (T_d) and linear coefficients of expansion in the temperatures range of 25–300 °C (α_25–300) were measured for subsystems along the B₂O₃ join of 10, 20 and 30 mol%. For these subsystems, T_g ranged from 411 to 522 °C, and T_d ranged from 453 to 563 °C, both decreasing with increasing Bi₂O₃ content. The measured α_25–300 ranged from 53 to 95 × 10⁻⁷ °C⁻¹, with values increasing with increasing Bi₂O₃ content. The ZnO content had the opposite effect to the Bi₂O₃ content. It appears that Bi³⁺ acts as a glass-modifier in this quaternary system.     

New evidence for tetrahedral triclusters in aluminosilicate glasses

The formation of thermodynamically stable 3/2-mullite (3 Al₂OAl₃·2 SiO₂) was investigated by scanning electron microscopy using reaction couples consisting of 2/1-mullite (2 Al₂O₃·1 SiO₂) plus SiO₂ glass, or Na₂O-SiO₂ glass, respectively. The mullite substrates were partially dissolved, thus leading to Al incorporation in the siliceous phases. In both reaction couples thin layers of stoichiometric 3/2-mullite form on the 2/1-mullite substrates. However, the major mullitization steps are different: The 2/1-mullite/SiO₂ reaction couple gives rise to 3/2-mullite crystallization within the bulk of the glass, whereas epitactic growth of c-axis orientated 3/2-mullite needles on the 2/1-mullite substrate was observed in the presence of Na₂O-SiO₂ glass. The differences in mullite nucleation were attributed to the existence or non-existence of tetrahedral triclusters in the as-reacted non-crystalline Al₂O₃-SiO₂ and Na₂O-Al₂O₃-SiO₂ phases, respectively. Triclusters of (Si,Al)O₄-tetrahedra in the Al₂O₃-SiO₂ glass may act as nuclei for 3/2-mullite crystallization in the bulk of the glass since these structural units also occur in mullite. In Na₂O-Al₂O₃-SiO₂ glasses triclusters are absent, and epitactical 3/2-mullite formation on the mullite substrate becomes more favorable energetically.     

Crystal growth of barium aluminum (gallium) borates

Crystals listed in the JCPDS card in the BaO‐B₂O₃‐Al₂O₃ and BaO‐B₂O₃‐Ga₂O₃ systems are of interest from a viewpoint of the Second Harmonic Generation (SHG). Ba₅Al₄B₁₂O₂₉ and Ba₅Ga₄B₁₂O₂₉ are promising new crystals with SHG activity and with congruent melting mode. These crystals can be grown by the Czochralski method with a size of 3 × 3 × 0.1‐1mm. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cryoscopic Investigation of Lead Oxide Mixtures with Garnet Forming Oxides,Garnets, and Related Oxide Compounds

The freezing point depression of PbO as solvent caused by the trivalent oxides and oxide compounds Fe₂O₃, Ga₂O₃, Al₂O₃, Bi₂O₃, Y₂O₃, Gd₂O₃, La₂O₃, YFeO₃, Fe₃O₄, Y₃Fe₅O₁₂, Gd₃Ga₅O₁₂, and PbFe₁₂O₁₉ allows to determine the number of particles which are formed from these compounds in the diluted solutions. — We have measured the liquidus temperatures of binary mixtures with the help of a DTA-equipment. In this way the cryoscopic constant K̄_c = 121 ± 16 K · kg · mole⁻¹ of PbO was determined by addition of ZnO, Cu₂O, PbSO₄, and PbF₂, respectively. The experimental results show that the oxides and oxide compounds dissociate in particles which contain only one cation of the solved compound.     

Characterization of SHG candidate crystals in barium aluminum (gallium) borates

Crystals listed in the JCPDS card in BaO‐B₂O₃‐Al₂O₃ and BaO‐B₂O₃‐Ga₂O₃ systems were synthesized by means of a solid‐state reaction method and a liquid‐state reaction method. Synthesized crystals were characterized from a viewpoint of Second Harmonic Generation (SHG) and crystal growth possibility. Ba₅Al₄B₁₂O₂₉ and Ba₅Ga₄B₁₂O₂₉ are promising new candidate crystals from the viewpoint of SHG activity and congruent melting behavior. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,characterization, single crystal X-ray diffraction and DFT studies of ethyl 5-methyl-1-phenyl-1H-pyrazole-4-carboxylate

The present study describes the synthesis, spectroscopic, and single crystal X-ray structural analysis of ethyl 5-methyl-1-phenyl-1H-pyrazole-4-carboxylate. The pyrazole ester of formula [C₁₃H₁₄N₂O₂] was prepared from the three-component one-pot condensation reaction of ethyl acetoacetate, N,N-dimethyldimethoxymethanamine, and phenyl hydrazine. The product was crystallized by using ethanol as solvent. The structure of the compound was confirmed by elemental analysis, Fourier transforms infrared (IR), thermogravimetric analysis, UV-visible (UV-Vis), ¹H NMR, and single-crystal X-ray diffraction studies. The gas-phase molecular geometry and the electronic structure-property of the molecule were calculated at the density functional theory. The frontier molecular orbitals, theoretical UV-Vis, and IR stretching vibrations were also reported. The compound crystallizes in the monoclinic system with the space group P2₁/c and Z = 4. The unit cell parameters are a = 12.141(3) Å, b = 13.934(4) Å, c = 7.2777(18) Å, and β = 97.816(14)⁰. The structure is stabilized by an intermolecular interaction of type C-H···O and the structure also involves C-H···π interactions.     

Effects of synthesis conditions on the yields and properties of HZSM‐5

In the SiO₂‐Al₂O₃‐TPAOH‐NH₄OH system through a two‐step procedure, the effects of synthesis parameters on the yields and properties of HZSM‐5 were studied. As the feeding n(SiO₂)/n(Al₂O₃) ratio increased, the yields of synthesized samples were between 11% and 14% while the crystallinity tended to decrease at the ratio > 300. At the ratio of 150, the yield was 13.7% and the ratio of actual yield to theoretical yield was 93%. The sample shaped ellipse‐like particles of 3 × 10⁻⁶ m. At the n(NH₃)/n(SiO₂) ratio of 1.5, the yield was 13.1% and the sample showed regular ellipse‐like particles of 2 × 10⁻⁶ m. Too high dosage of NH₄OH lowered the yield and the crystallinity. The addition of seed crystal favored the HZSM‐5 synthesis in high crystallinity. At the addition amount of 4%, the yield reached 13.9% and the sample shaped in spherical particles of 0.5 × 10⁻⁶ m. Synthesized HZSM‐5 with a surface area of 455 m²·g⁻¹ and intrinsic acidity showed highly catalytic activity toward the methanol conversion to olefins reaction.     

Vibrational spectra of crystals of bismuth borates

The vibrational spectra of crystals of bismuth borates Bi₂₄B₂O₃₉, Bi₄B₂O₉, BiBO₃, and Bi₂B₈O₁₅ were obtained for the first time, and the spectra of Bi₃B₅O₁₂ and BiB₃O₆ crystals measured in the range 30–1600 cm^?1 at room temperature were refined. The lines observed were assigned to the corresponding vibrational transitions on the basis of the theoretical group analysis and comparison of the obtained results with the vibrational spectra of borates of different composition. The complication of the structure of bismuth borates with increasing content of B₂O₃ was traced by the example of vibrational spectra.     

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)     

Quenched glasses in the systems of Li2O with Al2O3, Ga2O3 and Bi2O3

By rapid quenching in a twin roller apparatus, glass was found to occur widely in the systems of Li₂O with Al₂O₃, Ga₂O₃, Bi₂O₃ and in mixed systems. Examination of the resulting flakes by X-ray powder diffraction, differential thermal analysis, and capacitance data revealed the occurrence of glass, glass transitions, crystallization exotherms and the nature of some of the crystallization paths.The log ionic conductivity of the glasses was found to follow a linear relationship with the Li concentration. Evidence was observed for three new metastable crystalline phases, one in the Li₂OAl₂O₃ system and two in the Li₂OBi₂O₃ system. The latter system also showed evidence for the occurrence of two glasses at almost all compositions.     

Phase segregation of non-stoichiometric aluminosilicate gels characterized by Al and Si MAS-NMR

Polymeric aluminosilicate gels with Al₂O₃/SiO₂ molar ratios of 1.3/2, 2.5/2, 3/2 and 4.7/2 were prepared by gelling a mixture of tetraethoxysilane and ethyl acetoacetate aluminium diisopropoxide. Mullite, without any other crystalline phase, directly crystallizes from the gel matrix at about 1000 °C for all investigated samples. The Al₂O₃ or SiO₂ crystalline phase can only be detected at relatively high temperatures accompanying the modification of mullite in the lattice structure. ²⁷Al and ²⁹Si MAS-NMR studies indicate that segregation of Al and Si atoms occurs in all samples below 900 °C in the amorphous state, regardless of the gel composition. However, the species of segregated units are very different and strongly dependent on the composition of the starting gels. This segregation may not cause the exothermic effect in differential thermal analysis examination, but it appears to be responsible for the composition change behavior of crystalline mullite with different heat treatment.     

Semi-quantitative analysis for FTIR spectra of Al2O3-PbO-B2O3-SiO2 glasses

A series of glass of the molar formula xAl₂O₃-(50-x)PbO-25B₂O₃-25SiO₂ with x:2.5–17.5 with step of 2.5 mol.% was prepared and measured for, density, molar volume and infrared absorption. A semiquantitative analysis of the IR spectra was performed. It was found that each oxide would contribute in density with a specific factor. The density factor related to PbO is markedly higher than that of the other two oxides represent the glass skeleton which means that the content of PbO is the main factor affecting the density. The depolymerization of the whole glass skeleton increases with increasing the content of Al₂O₃. There is a competition between the role of PbO and Al₂O₃ in changing the value of N₄ and the crosslinking of the glass network. The silicate network tends to be distinguished from the reminder of the whole glass network with increasing alumina. The IR band located near 700 cm^? 1 was suggested to be due to the vibrations of bridging oxygens between trigonal boron atoms. An essential change in the role of PbO in these glasses from glass modifier to glass former occurred around 12 mol.% Al₂O₃.     

X-ray absorption and Raman characterizations of TeO2-Ga2O3 glasses

The thermodynamic properties of transparent glasses prepared in the TeO₂-Ga₂O₃ system were investigated by differential scanning calorimetry. The change of the thermal parameters as a function of the chemical composition is discussed. Raman and both Te L_III and Ga K edge X-ray absorption spectroscopies at room temperature were used to examine the short range order. Analyses of the spectra suggest that the addition of Ga₂O₃ content to the TeO₂ glass matrix induces the transformation of trigonal bipyramids (TeO₄E, E=lone electronic pair 5s² of Te) to trigonal pyramids (TeO₃E) with formation of Te-O-Ga bridging bonds. Furthermore, Ga K edge XANES and EXAFS studies show that Ga atoms exhibit both tetrahedral (GaO₄) and octahedral (GaO₆) environments.