BO4 Tetrahedra Research Articles

Manganese agglomeration and radiation damage in doped Li2B4O7

Manganese clustering effects were studied in Li2B4O7 (LTB) ceramics. The samples LTB:Me + Mn (Me = Sn, Cu, Mn, Zn, Be) were prepared by a two-stage doping method (except for LTB doped with Mn solely). EPR, pulsed cathodoluminescence, thermoluminescence (TL) were measured. Mn clustering causes supralinearity of the material response to the radiation dose, reversible shift of the dosimetric TL peak, and irreversible radiation damage. Radiation damage of the LTB crystal lattice is accompanied with the formation of a peroxide bridge instead of a single oxygen at the common vertex of two BO4 tetrahedra. Repelled by an excessive positive charge of a Mn cluster, holes are localized around at traps including the peroxide bridges where they are stable up to 630 K. The extent of the radiation damage can be estimated by the intensity of the high-temperature TL at 630 K, when the released holes recombine with the electrons near regular Mn2+. The most stable against the radiation damage and also suitable for TL dosimetry is LTB:Sn + Mn.

Structural FTIR spectra and thermal properties of CdO–B2O3 glasses doped with LiF, CaF2 or TiO2, together with X-ray diffraction and SEM investigations of their glass–ceramic derivatives

Binary cadmium borate (CdO 40–B2O3 60 mol%) glass together with samples with the same basic composition and doped with 2% of either LiF, CaF2 or TiO2 were prepared by melting-annealing technique. Samples of these prepared glasses were thermally heat-treated to convert them to their corresponding glass–ceramic derivatives. FTIR spectral measurements were carried out to identify the constitutional network building units. IR results indicate the identification of both triangular BO3 and tetrahedral BO4 groups in their characteristics vibrational different wavenumbers. These IR vibrational spectra were assigned to their origin and they confirm that CdO like any alkali or alkaline earth oxide shares in the modification of some BO3–BO4 groups to their specific limit. The dopants show minor variations on the IR spectra due to their low percent. X-ray diffraction patterns identify the crystalline phases which were separated during thermal heat-treatment and the dopants were efficient in acting as nucleating agents and sharing in the crystalline phases formed. The base glass–ceramic is composed of cadmium metaborate only while the dopants change this phase to cadmium pyroborate beside a lithium borate or calcium borate phases while with TiO2 forms brookite crystalline phase beside cadmium pyroborate. Thermal expansion measurements for the studied glasses reveal similar progressive increase in thermal expansion coefficient, but the dilatometric softening temperatures exhibit distinct decrease with the dopants supporting the assumption that the dopants are situated in modifying positions. SEM technique was performed to ensure the morphological structures which exist along with addition of different dopants.

Speciation Change of Uranyl in Lithium Borate Glasses

Determining the uranyl(VI) UO22+ reactivity in crystalline and amorphous oxides is necessary to control its mobility. The intrinsic versatility of borate structural units containing both triangular BO3 and tetrahedral BO4 makes them original and rich hosts for uranyl. As part of the effort to determine the uranium stability in borate oxides, we have determined the speciation of uranium(VI) in two lithium borate glasses containing, respectively, 10 mol % and 30 mol % Li2O using a combined structural and spectroscopic approach based on X-ray absorption spectroscopy (XAS). M4- and L3-edge high-resolution XAS demonstrates the speciation of U(VI) as uranyl in both glasses. Comparison of uranyl bond distances obtained by EXAFS with distances found in borate crystals reveals that in the low alkali borate glass, uranyl is present as hexagonal bipyramids with six equatorial oxygen ligands. This local environment was never observed in any other oxide glass. We show that the increase of the lithium content induces the decrease of the equatorial coordination number. The associated uranyl bond elongation suggests the influence of the alkali cations in relation with drastic changes in the structure of the borate network. The spectroscopic evidence of this speciation change is discussed in terms of change in the uranyl electronic structure and covalency.

Crystal structure of calcium vanadate-phosphate fluoride

Apatite-type materials AI4AII6(BO4)6X2 have two unique cations sites AI and AII, which can host large mono-, di- tri- and tetra-valent cations. The average cation radii will affect the twist angle and lattice constants. However, there are few reports on the influence of B site substitutions on the twist angle and lattice parameters. It is believed that the lattice constant variation as a function of B site substitutions may not follow the same twist-angle model as proposed for A site. This work reports our results on the crystal chemistry of synthetic apatite Ca10(VxP1−xO4)6F2 obtained through the crystal structure characterization using Rietveld refinement and high-resolution transmission electron microscopy. The quantification of vanadium/phosphorus partitioning in BO4 tetrahedra showed that equilibrium with more than 70% substitution of phosphorous by vanadium was difficult to achieve unless longer annealing (about 1 week at 900 °C) was employed. In comparison with the apatites with different ionic radii at AI and AII sites, Ca10(VxP1−xO4)6F2 apatites with different ionic radii at B site show little twist angle variation for the whole series, which indicates that the dilation of unit cell constants is mainly because of the expansions of BO4 tetrahedra when A site cation is fixed.

Thermal expansion of ammonium pertechnetate and ammonium perrhenate

The thermal expansion of NH4TcO4 and NH4ReO4 between 97 and 500 K has been established using variable temperature synchrotron X-ray diffraction. Both oxides display a tetragonal scheelite-type structure over the temperature range. The observed anomalous thermal expansion is associated with disorder in the orientation of the NH4 groups and the presence of anisotropic, equatorial and axial, interactions between the H atoms and the BO4 tetrahedra. The importance of the hydrogen interactions was verified by a study of the isostructural compound NaReO4 over a similar temperature range. The differences in the details of the Negative Thermal Expansion (NTE) behaviour of NH4TcO4 and NH4ReO4 is a consequence of differences in the HBO4 interactions due to changes in the BO bond lengths within the BO4 groups. Both ammonium salts decompose when heated above ∼500 K.

Crystallographic Analysis of the Datolite (CaBSiO4OH) to Okaymalite (Ca2B2SiO7) Structural Transformation under Dehydration

The common “template” of datolite and okayamalite structures is a column-ribbon formed by alternating empty and Si occupied oxygen tetrahedra interconnected by common edges. The columns consolidate with their environment into crystalline structures largely due to the influence of the local symmetry of SiO4 and BO4 tetrahedra. As a result, mirror symmetry pseudo-planes of monoclinic datolite transform into okayamalite m planes; the pseudo-axis $\bar 4$ becomes the principal axis, whereas both structures contain glide planes and cation sublattices close in size.

Dipotassium tetrahydroxidopentaoxidotetraborate monohydrate

In the tetraborate anion of the title compound, K2[B4O5(OH)4]·H2O, the bridging B—O bond lengths of the tetrahedral BO4 and the trigonal-planar BO3 units are slightly longer than the corresponding terminal B—OH bond lengths. The crystal structure is stabilized by intermolecular O—H...O, O—H...Owater and Owater—H...O hydrogen bonds, generating a three-dimensional network. The two potassium cations both show a coordination number of 9.

High‐Pressure Synthesis and Crystal Structure of the Highly Condensed Yttrium Borate YB7O12

The yttrium borate YB7O12 was obtained in a high‐pressure/high‐temperature experiment at 10 GPa and 1573 K. The crystal structure was clarified by X‐ray single‐crystal diffraction, where the compound was found to crystallize in the orthorhombic space group Pccn (no. 56) with the lattice parameters a = 11.985(2), b = 6.717(6), c = 7.867(7) Å, and a volume of V = 633.0(1) Å3. Built up exclusively from BO4 tetrahedra, YB7O12 features an exceptionally high degree of condensation, which originates from the finding that every tetrahedron contains two threefold‐coordinated oxygen atoms. The compound was further characterized by X‐ray powder diffraction.

Vitrified Municipal Waste for the Immobilization of Radioactive Waste: Preparation and Characterization of Borosilicate Glasses Modified with Metal Oxides

Municipal solid waste is used as a raw material for the production of borosilicate glasses by melting annealing technique. Many chemical and physical measurements are studied to test their possibility in the immobilization of radioactive wastes. The results show good behaviors against gamma radiation doses such as suitable density and microhardness values, stable behaviors towards low and high doses of gamma radiation indicated by IR and EPR techniques. As well as good chemical durability in H2O and NaOH leaching solutions. The network structure of borosilicate glasses consists of tetrahedral silicate units SiO4 and the triangle BO3 or tetrahedral BO4 groups which strengthen the structure of glasses and enhance their desired properties for achieving the goal of immobilizing nuclear wastes.

Structure and microstructure characterization of the La2SrB10O19 glass-ceramics

The crystal structure of new lanthanum strontium borate glass-ceramics was refined by the Rietveld method. The results showed that La2SrB10O19 has the monoclinic crystal structure, space group C2 (No. 5) with a = 11.1170(6), b = 6.5667(3), c = 9.2363(3) ?, ? = 91.481?, V = 674.04(7) ?3, two formula units per unit-cell, and density 3.830 g cm?3. The main building units of the crystal structure are BO4 tetrahedra and BO3 triangles. Clusters composed of [B5O12] form an infinite double layer running perpendicular to the c-axis. Lanthanum atoms, situated in [B5O12]n layers, are coordinated with 10 oxygen atom in a form of LaO10 polyhedra, while Sr atoms, located between [B5O12]n layers, are coordinated with 8 oxygen atoms in a form of SrO8 polyhedra. Microstructural measurements contain both crystallite domain sizes and microstrain calculations obtained by the Warren-Averbach and the simplified integral-breadth methods.

X-ray Induced Luminescence and Physical Properties of Lithium Lanthanum Borate Glass Doped with Ce3+ for Radiation Detection Material

Abstract Lithium lanthanum borate glasses doped with different concentration of Ce3+ were synthesized to study the luminescence and physical properties. Glass density was measured by Archimedes’ principle and taken to evaluate the molar volume. Density and molar volume value increases with increasing of Ce3+ concentration. Glass network of borate former, tetrahedral BO4 and trigonal BO3, was proved by Fourier transform infrared spectroscopy. From absorption spectra, these glasses can absorb the ultraviolet radiation. The luminescence spectra under x-ray induction show that glasses emit the photons in the range of 360 – 530 nm wavelength. These emissions correspond to the 5d - 2F5/2 and 5d - 2F7/2 transitions of Ce3+. The luminescence decay curves were observed and fitted the fast life time values in the order of ten nanoseconds. This Ce3+ doped glass performs the interesting properties which can be developed for using as a scintillator in x-ray detection device.

Structural Characteristics of a Family of Bioactive Glasses Formed by Replacing Varying Amounts of SiO 2 in 45S5 Glass with B 2O 3

Bioactive glasses with controllable reactivity and bioactive potential have been created by replacing varying amounts of SiO2in silicate 45S5 glass with B2O3. While these borate and borosilicate glasses formed from 45S5 glass are receiving growing interest for hard and soft tissue repair, their structural characteristics have received little attention. In this study, the structural characteristics of a family of bioactive glasses formed by replacing varying amounts of SiO2 in 45S5 glass with B2O3 were evaluated using multiple spectroscopic techniques. A benefit of this work is the use of multiple spectroscopic techniques and one set of compositional variation for a widely used family of bioactive glasses. The results showed that when compared to 45S5 glass, SiO2 remained the primary network in a borosilicate glass designated 45S5-1B, formed by replacing 33.3 mol. % of the SiO2 in 45S5 with B2O3. The glass network in both glasses was composed mainly of SiO4 tetrahedral units with 2 nonbridging oxygen atoms. In comparison, B2O3 was the primary network former in borosilicate 45S5-2B and borate 45S5-3B glasses, formed by substituting 66.7 mol. % and 100 mol. %, respectively, of SiO2 in 45S5 glass with B2O3. The network in these two glasses was composed mainly of trigonal BO3 structural units (orthoborate or pyroborate groups) and a smaller fraction ∼30%) of tetrahedral BO4 units. The observed structural characteristics are used to rationalize data from a previous study for the reactivity and bioactive potential of this family of bioactive glasses.

The effect of boron substitution for aluminium on the microstructure of calcium fluoro-aluminosilicate glasses and glass-ceramics

Calcium fluoro-aluminosilicate (4.5SiO2-3Al2O3-1.5P2O5-3CaO-2CaF2) glasses have significant applications in the medical and dental fields. However, due to the biological hazard of aluminium in the human body, this study focused on the influence of boron substitution for aluminium on the structure and properties of a series of substituted glasses and their correlated glass-ceramics. The results indicated that by increasing the amount of boron, the density of glasses and their glass-ceramics both decreased, whereas the number of bridging oxygens in the glasses increased. The glass transition temperature and the crystallization temperature remained almost unchanged for the glasses with a boron substitution of less than 25 mol%. Boron formed oxygen bridges in all glasses in the form of BO3 triangles and BO4 tetrahedra. Reducing the Al content in glasses, had an effect on the morphology and orientation of the fluorapatite crystal phase formed.

Synthesis and Characterization of the First Tin Fluoride Borate Sn3 [B3 O7 ]F with Second Harmonic Generation Response.

The new non‐centrosymmetric tin fluoride borate Sn3[B3O7]F was synthesized hydrothermally, and was characterized by single‐crystal and powder X‐ray diffraction, vibrational spectroscopy, DFT calculations, second harmonic generation (SHG) measurements, thermogravimetry, and differential scanning calorimetry. Its SHG response is about 12 times that of quartz. The compound crystallizes in the non‐centrosymmetric orthorhombic space group Pna21 with lattice parameters a=922.4(2), b=769.8(4), and c=1221.9(6) pm (Z=4). Characteristic for the structure are isolated B3O7 moieties, consisting of two corner‐sharing BO3 units and one BO4 tetrahedron. These occupy half of the octahedral voids of a slightly distorted hexagonal closest packing of Sn2+ atoms, with [SnF]+ units in the other half of the octahedral voids. Sn3[B3O7]F is transparent over a wide spectral range with a UV cut‐off edge at about 263 nm.

Comprehensive studies of the Ag+ effect on borosilicate glass ceramics containing Ag nanoparticles and Er-doped hexagonal NaYF4 nanocrystals: morphology, structure, and 2.7 μm emission

AbstractIn this work, we have performed a comprehensive investigation of the Ag+ concentration effect on the morphological, thermal, structural, and mid-infrared emission properties of novel oxyfluoride borosilicate glasses and glass ceramics containing both Ag nanoparticles and erbium-doped hexagonal NaYF4 nanocrystals. The effect of Ag+ ions on the glass forming and crystallization processes was discussed in detail by glass structural analysis. It was found that the Ag+ concentration can affect the distribution of Na+ ion and bridge oxygen in boron-rich and silicon-rich phases, which induced the transformation between BO3 triangles and BO4 tetrahedra during crystallization process. In addition, there was a turning point when the doped Ag+ ion concentration reached its solubility in the borosilicate glass. Furthermore, the enhancement of the 2.7 μm emission and the reduction of the lifetime of the 4I13/2 level were observed both in glasses and in glass ceramics, and its origin was revealed by qualitative and quantitative analyses of the Er3+-Ag nanoparticles (localized electric field enhancement) and Er3+-Er3+ (nonradiative resonance energy transfer) interactions within glasses and glass ceramics. Moreover, the high lifetime of the 4I11/2 level (2.12 ms) and the peak emission cross section in 2.7 μm (6.8×10−21 cm2) suggested that the prepared glass ceramics have promising mid-infrared laser applications.

Synthesis and Crystal Structure of the Acentric Indium Borate InB6O9(OH)3.

The new acentric indium borate InB6O9(OH)3 was synthesized in a Walker-type multianvil apparatus at extreme pressure and temperature conditions of 12.3 GPa and 1500 °C. Single-crystal X-ray diffraction provided the data for the crystal structure solution and refinement. InB6O9(OH)3 crystallizes in the orthorhombic space group Fdd2 ( Z = 8) with the lattice parameters a = 39.011(8), b = 4.4820(9), c = 7.740(2) Å, and V = 1353.3(5) Å3. The structure of InB6O9(OH)3 is basically built of corner-sharing BO4 tetrahedra and isolated InO6 octahedra. The presence of hydroxyl groups was confirmed with vibrational spectroscopic methods (IR and Raman). Furthermore, the second harmonic signal of an InB6O9(OH)3 powder sample yielded more than twice the intensity of quartz.

Concentration effect on the structural and spectroscopic investigations of Sm3+ ions doped B2O3–Bi2O3–CaF2–Na2O glasses

A new series of Sm3+ ions doped sodium fluoroborate glasses have been synthesized following the melt quenching technique. The structural analyses were made recording XRD and FTIR spectra. The XRD pattern reveals the amorphous nature and the FTIR spectra explore the presence of various functional groups such as B–O asymmetric stretching of trigonal BO3 units, B–O stretching of tetrahedral BO4 units and vibrations of Bi–O− bond in the BiO6 octahedral units. The luminescence properties have been explored through UV–vis–NIR, luminescence and decay spectral measurements. The Judd-Ofelt intensity parameters (Ω2, Ω4, Ω6) were determined from the absorption spectra to investigate the nature of metal-ligand bond and symmetry around the Sm3+ ion site. In order to elucidate the potential applications of the present Sm3+ ions doped glasses the radiative properties such as transition probability (A), effective band width (Δλeff), stimulated emission cross-section (σpE) and branching ratio (βR) for the 4G5/2→ 6H5/2, 6H7/2, 6H9/2 emission levels were determined and compared with the reported literature. The luminescence quenching for the prominent 4G5/2→6H7/2 emission transition have been observed while increasing the Sm3+ ions concentration beyond 0.5wt%. The decay rates for the 4G5/2 level of the Sm3+ ions exhibit non-exponential behavior for all the prepared glasses except for the 0.05wt% Sm3+ glass and fitted to Inokuti-Hirayama model to understand the predominant energy transfer mechanism takes place among the Sm3+ ions. It is observed from the determined stimulated emission cross-section and branching ratio values that, of all the studied glasses CNFB0.5S glass can be used as a potential candidate for the development of reddish-orange lasers.

Relaxation oscillation of borosilicate glasses in supercooled liquid region

Most supercooled non-polymeric glass-forming melts exhibit a shear thinning phenomenon, i.e., viscosity decreases with increasing the strain rate. On compressing borosilicate glasses at high temperature, however, we discovered an interesting oscillatory viscous flow and identified it as a typical relaxation oscillation caused by the peculiar structure of borosilicate glass. Specifically, the micro-structure of borosilicate glass can be divided into borate network and silicate network. Under loading, deformation is mainly localized in the borate network via a transformation from the three coordinated planar boron to trigonal boron that could serve as a precursor for the subsequent formation of a BO4 tetrahedron, while the surrounding silicate network is acting as a stabilization/relaxation agent. The formation of stress oscillation was further described and explained by a new physics-based constitutive model.

Synthesis, structure and characterization of a new nonlinear optical calcium borate [Ca2B5O9]·[H(OH)2

A new nonlinear optical crystal [Ca2B5O9]·[H(OH)2] (1) has been synthesized under hydrothermal condition. Compound 1 crystallizes in the monoclinic space group C2 with lattice constants a=10.111(2) Å, b=7.754(11) Å, c=6.198(14) Å, β=127.04(3)° and Z=2. The fundamental building block (FBB) of 1 is a [B5O12] unit with two BO3 triangles and three BO4 tetrahedra. 1 was characterized by single-crystal X-ray diffraction, IR and UV–Vis spectroscopy, thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD) respectively. Also, powder second harmonic generation (SHG) measurements indicate that 1 is phase matchable and displays a SHG response of about 3.5 times that of KDP (KH2PO4).

Li4B4M3O12Cl (M = Al, Ga): An Electrochemically Stable, Lithium-Ion-Conducting Cubic Boracite with Substituted Boron Sites

Abstract A cubic boracite with substituted boron sites, Li4B4M3O12Cl (M = Al, Ga), derived by fully replacing the tetrahedral BO4 units in the parent lithium chloroboracite, Li4B7O12Cl, with AlO4 or GaO4 units, has been discovered. These substituted compounds have the largest unit cell dimensions of known boracites and are formed as the stable primary phase in highly crystalline glass-ceramics derived from the Li2O–B2O3–M2O3–LiCl quarternary system. The conductivity of Li4B4M3O12Cl glass-ceramics at room temperature was ∼10−5 S cm−1, an order of magnitude larger than the highest conductivity recorded for Li4B7O12Cl glass-ceramics. The Li4B4Al3O12Cl glass-ceramic is stable in contact with Li metal and exhibits a wide electrochemical window between 0 and 6 V vs. Li/Li+ and a Li+ ion transport number of ∼1.