Stabilization of heavy metals fluoride glasses

A new class of fluoride glasses has been isolated in the ternary system containing one transition metal fluoride ZnF₂, one rare earth fluoride YbF₃ and one actinide fluoride ThF₄. The controlled addition of BaF₂ playing the role of modifier allows the stabilization of glasses with low rate of crystallization in the quaternary system BaF₂ThF₄ZnF₂YbF₃. The infrared transmission can be extended to the 7–8 μ region, a significant improvement over the fluorozirconate glasses.     

Crystallization and spectroscopic properties of Eu-doped CaF2 nanocrystals in transparent oxyfluoride glass-ceramics

Transparent oxyfluoride glass-ceramic in the system SiO₂–Al₂O₃–CaF₂–EuF₂ containing Eu-doped CaF₂ nanocrystals were produced by using the controlled crystallization of melt-quenched glass. X-ray diffraction and transmission electron microscopy data have revealed the formation of the CaF₂ nanocrystals of about 65 nm size. Photoluminescence spectra have shown an increase of the splitting of the luminescences associated to the Eu³⁺ ion along with annealing time which is consistent with the Eu³⁺ environment evolving from a glassy to a crystalline state.     

Spectroscopic properties of Er-Yb co-doped glass ceramics containing BaF2 nanocrystals

A Er³⁺ and Yb³⁺ co-doped transparent oxyfluoride glass ceramic containing BaF₂ nanocrystals has been prepared. The formation of BaF₂ nanocrystals in the glass ceramic was confirmed by X-ray diffraction. Intense upconversion luminescence in the Er³⁺ and Yb³⁺ co-doped glass ceramic could be observed. Stark splitting of the Er³⁺ upconversion luminescence peaks in the glass ceramic indicated that Er³⁺ and Yb³⁺ had been incorporated into the BaF₂ nanocrystals. Near infrared luminescence decay curves showed that the Er³⁺ and Yb³⁺ co-doped glass ceramic had higher luminescence efficiency than the precursor glass.     

Thermal Expansion of SrF2 at Elevated Temperatures

The X-ray method was used to determine the linear thermal expansion coefficient of SrF₂ in the temperature range from 301 to 1173 K. A comparison of the thermal expansion coefficients of CaF₂, SrF₂ and BaF₂ at T > 300 K shows that the degree of lattice an–harmonicity in the alkaline earth fluorides decreases with increasing mass of the alkaline earth atom. The results for the thermal expansion of SrF₂ are used to discuss the temperature dependence of the lattice mismatch in the SrF₂/InP film–substrate system.     

Glasses in the system of MnNbOF5–BaF2–BiF3–ErF3

The glasses in the MnNbOF₅–BaF₂–5BiF₃–ErF₃ system were obtained and their thermal and optical properties were studied. The specialties of crystallization depending on system composition are showed. The glass structure is discussed based on results of the IR and Raman spectra study. During the studies of inelastic light scattering, there revealed a strong photoluminescence, produced by erbium emission, whose intensity depends not only on the erbium trifluoride content in glass, but also on the glass network structure.     

Structural analysis and devitrification of glasses based on the CaO-MgO-SiO2 system with B2O3, Na2O, CaF2 and P2O5 additives

Glasses, whose basic composition was based on the CaO-MgO-SiO₂ system and doped with B₂O₃, P₂O₅, Na₂O, and CaF₂, were prepared by melting at 1400 °C for 1 h. Raman and infrared (IR) spectroscopy revealed that the main structural units in the glass network were predominantly Q¹ and Q² silicate species. The presence of phosphate and borate units in the structure of the glasses was also evident in these spectra. X-ray analysis showed that the investigated glasses devitrified at 750 °C and higher temperatures. The crystalline phases of diopside and wollastonite dominated, but weak peaks, assigned to akermanite and fluorapatite, were also registered in the diffractograms. The presence of B₂O₃, Na₂O, and CaF₂ had a negligible influence on the assemblage of the crystallized phases, but it caused a reduction of crystallization temperature, comparing to similar glasses of the CaO-MgO-SiO₂ system.     

The influence of CaF2 content on the physical properties and apatite formation of bioactive glass coatings for dental implants

This report details the physical properties, bioactivity and biocompatibility of manufactured glasses containing a range of calcium fluoride (CaF₂) concentrations. Compositions were based on the following system: SiO₂, CaO, Na₂O, K₂O, P₂O₅, ZnO and MgO, and in total seven glasses were synthesized using a melt–quench route. The ratio of the base compounds was kept constant, but had increasing CaF₂ concentrations (0.00, 2.44, 4.77, 9.11, 10.33, 11.53 and 13.00 mol%). Glasses were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and dilatometery. Density was quantified according to Archimedes method and apatite formation tested following immersion in simulated body fluid (SBF) and Tris-buffer solution. Glass coatings were prepared by enamelling technique using 10 mm in diameter pure titanium disks. XRD demonstrates that all glasses are amorphous and that the sintering window, glass transition and softening temperatures decrease with increasing CaF₂ content. In contrast, thermal expansion coefficient and glass density increase with CaF₂ content. After 1 week immersion in SBF and Tris, XRD and Fourier transform infrared (FTIR) spectroscopy showed that the surfaces of all glasses underwent structural changes with evidence of surface apatite formation. Fluoride-electrode analysis indicates that the amount of fluoride released was proportional to the original CaF₂ content. The survival and growth of osteoblasts on the surface of these glasses is consistent with biocompatible characteristics.     

Fluoride-containing bioactive glasses: Fluoride loss during melting and ion release in tris buffer solution

Melt-derived bioactive glasses (SiO₂-P₂O₅-CaO-Na₂O-CaF₂; CaF₂ 0 to 17.76 mol%) lost fluoride during melting, but nominal and analysed CaF₂ contents in the glass correlated linearly. Analysed CaO contents were increased, showing that fluoride was lost as hydrofluoric acid after reaction with atmospheric water during melting. Weight loss on ignition reduced linearly with increasing CaF₂, suggesting that CaF₂ impedes absorption of atmospheric water. pH changes in tris buffer solution showed that pH is controlled by the silicate matrix (via ion exchange processes), and fluoride release contributes less to the overall pH. Glasses formed apatite in tris buffer; phosphate concentration of the glass was the limiting factor, resulting in fluorite formation for increasing fluoride content in the glass and calcite formation for the fluoride-free composition. These results allow for tailoring of novel fluoride-containing bioactive glasses to address specific needs, particularly in dentistry and for remineralising toothpastes.     

Structure and non-linear optical properties of BaO–TiO2–SiO2 glass containing Ba2TiSi2O8 crystal

The BaO–TiO₂–SiO₂ crystallized glass containing Ba₂TiSi₂O₈ crystal phase was examined using X-ray diffraction (XRD) measurement and Maker fringe technique. It has been found that the crystallized glasses with a composition of close to the stoichiometric Ba₂TiSi₂O₈ showed bulk crystallization, whereas other crystallized glasses with non-stoichiometric composition of Ba₂TiSi₂O₈ showed surface crystallization. The parameter ΔT, the difference in temperature between the crystallization onset and the glass transition temperature, strongly affects the crystallization behaviors of the present BTS glasses. The 30BaO–20TiO₂–50SiO₂ transparent surface crystallized glass with strong c-oriented Ba₂TiSi₂O₈ phase showed its second-order non-linear optical constant, d₃₃ = 6.1 pm/V.     

Vibrational spectra and structure of chloro-fluorozirconate glasses

A series of barium chloro-fluorozirconate glasses have been prepared. Their IR absorption, IR reflectivity and Raman spectra have been measured down to 33 cm^?1. The glass transition and crystallization temperatures have also been measured. The high frequency IR absorption and Raman modes of the chloro-fluorozirconate glasses have been assigned as in fluorozirconate glasses. The IR reflection spectra of chloride-containing glasses differed from the fluorozirconates in that one band was clearly related to Cl atom motions. The structure of the glasses probably consists of zig-zag chains of ZrCl₂F₄ mixed halide octahedra plus a pure fluoride matrix whose structure is similar to that of a ZrF₄BaF₂ glass with the same composition.     

Crystallization process on amorphous GeTeSb samples near to eutectic point Ge15Te85

One of most important properties of some tellurium-based chalcogenide glasses is the optical and electrical switching between two states: the glass and the crystalline state. The understanding in these systems of the glass to crystal transition and its transformation kinetics is essential for their application in non-volatile memories. GeTeSb and GeTe amorphous samples of compositions close to the eutectic point Ge₁₅Te₈₅ were obtained by rapid solidification from the liquid state employing melt spinning technique. The glass forming ability of this system, for this cooling technique, is restricted to a small composition range nearby the binary eutectic. The crystallization kinetics of the samples was studied by means of differential scanning calorimetry (DSC) under both isothermal and continuous heating regimes. The quenched samples and the crystallization products have been characterized by X-ray diffraction with Cu(Kα) radiation. The crystallization temperature, activation energy, crystallization enthalpy and the dependence of these properties on concentration are reported. The crystallization study of Ge₁₅Te₈₅ glasses shows: a primary crystallization of Te superimposed with a secondary crystallization of GeTe. The addition of Sb (5 at.%) to the eutectic point Ge₁₅Te₈₅ modifies this behavior: the crystallization of Ge₁₃Sb₅Te₈₂ glasses consists on the crystallization of Te and Ge₂Sb₂Te_5. The crystallization of the ternary glasses was modeled.     

Crystallization of monoclinic WO3 in tungstate fluorophosphate glasses

Tungstate fluorophosphate glass compositions with high WO₃ concentration were prepared in the ternary system (80−0.8x)NaPO₃-(20−0.2x)BaF₂-xWO₃ with x = 40,50 and 60 mol%. Transparency decreases as WO₃ concentration increases but can be improved by addition of oxidizing systems such as CeO₂ or Sb₂O₃/NaNO₃. Characterizations by thermal analysis (DSC) point out that an increase in the amount of WO₃ results in a higher glass transition temperature. In addition, such compositions are very stable against devitrification since samples containing 40% and 50% of WO₃ donot even exhibit the expected crystallization event. In these samples, the stability against crystallization decreases with the WO₃ content and vitreous sample containing 60% of WO₃ exhibits an endothermic event around 620 °C due to crystallization of monoclinic WO₃ phase. In these glasses, it was shown that the nucleation stage can be induced by thermal-treatment when external nucleating agents such as Ti or Sb are used. Finally, gold-doped samples exhibit a higher crystallization tendency and monoclinic WO₃ phase can be grown in such glasses.     

Influence of alumina addition on crystallization and texturing behavior of LaBGeO5 glass

The structure and crystallization behavior of glasses with 25La₂O₃ · 25B₂O₃ · 50GeO₂ composition, melted in platinum (P glass) and corundum (A glass) crucibles, were studied by DTA, X-ray diffraction and FTIR spectroscopy. The Al₂O₃ dissolved from corundum crucible in the A glass was estimated to be in the range 5–7 wt%. This alumina content had almost no influence on glass transition temperature but strongly affected the structure and crystallization behavior of the A glass. In fact, the P glass showed good texture-forming ability: high quality textured glass-ceramic plates based on stillwellite-like LaBGeO₅ crystals were easily obtained. On the contrary, the presence of alumina stabilized the A glass from which binary phases crystallize first, and only afterwards they are transformed in stillwellite by secondary crystallization: so in this glass texturing is hindered. Crystallization and texturing behavior of P and A glasses were well related to FTIR data. P glass contained both threefold and fourfold coordinated boron while in the A glass the presence of aluminum forced boron to assume almost exclusively threefold co-ordination. Hence the easier crystallization of stillwellite phase and the good textures obtained from the P glass contrary to the A glass, can be well understood since all boron atoms have tetrahedral co-ordination in stillwellite LaBGeO₅ crystal.     

Luminescence behavior of Er ions in glass-ceramics containing CaF2 nanocrystals

The upconversion luminescence and near infrared luminescence of the Er³⁺ ions in transparent oxyfluoride glass-ceramics containing CaF₂ nanocrystals have been investigated. The formation of CaF₂ nanocrystals in the glass-ceramics was confirmed by XRD. The oscillator strengths for several transitions of the Er³⁺ ions in the glass and glass-ceramics have been obtained and then the Judd-Ofelt parameters were calculated. The split near infrared emission peaks of the Er³⁺ ions in the glass-ceramics can be observed because the Er³⁺ ions have been incorporated into crystalline environment of the CaF₂ nanocrystals. The upconversion luminescence intensity of Er³⁺ ions in the glass-ceramics increased significantly with increasing heat treated time. The transition mechanism of the upconversion luminescence has been ascribed to a two-photon absorption process.     

Raman scattering study of BaF2ZrF4FeF2 glasses

Several BaF₂ZrF₄ glasses containing 5 mol% FeF₂ have been studied to elucidate the fraction of nonbridging fluorine atoms (−F⁻) in a ZrF₆ octahedron constituting a zigzag chain. A continuous increase in the fraction of nonbridging fluorine atom in a ZrF₆ octahedron is deduced from the increase in the integrated peak intensity of the symmetric stretching-vibrational mode (ν^s) for the Zr-nonbridging fluorine atom when the BaF₂ (+ FeF₂) content is lower than 38 mol%, i.e., in the composition region where the average coordination number of Zr is regarded as six. This result is well consistent with the previous results obtained from Raman studies of binary BaF₂HfF₄ glasses, and also with those of Mössbauer and Raman studies of ternary BaF₂ZrF₄FeF₂ glasses. A drastic decrease in the symmetric-stretching vibrational mode (ν^s) in 42BaF₂·53ZrF₄·5FeF₂ glass suggests that a friction of ZrF₆ octahedron is reduced when BaF₂ (+FeF₂) content is close to 50 mol%. The zigzag chain is therefore considered to be constituted of ZrF₇ units in such glasses.     

An X-ray diffraction study of the structure of barium fluorozirconate and fluorohafnate glasses

Two binary glasses have been prepared in the ZrF₄BaF₂ and HfF₄BaF₂ systems, containing 64 mol.% ZrF₄ and 66 mol.% HfF₄, respectively. The two plate-like glass samples were studied by X-ray diffraction, and the resulting data were subjected to a Fourier analysis. The pair correlation functions thus obtained yield a ZrF (or HfF) nearest neighbor coordination number of ～ 7.6 for both glasses. The second peak in the correlation functions has been assigned to a combination of FF and BaF interactions, while the third peak is probably due in part to ZrZr (Hf-Hf) interactions. The diffraction data have been compared with the predictions of structural models for barium fluorozirconate and fluorohafnate glasses.     

Photoluminescent properties and Raman spectra of ZnO-based scintillating glasses

Glasses in SiO₂–ZnO–BaO system with the different ZnO/BaO ratio were studied. In some cases, BaF₂ was introduced to substitute for BaO on the equal base. Photoluminescent spectra showed that ZnO in glass matrices behaved somewhat differently from ZnO crystals. Especially, the introduction of fluorine ions led to dramatic shift of UV emission band of glasses closer to that of ZnO crystals. Raman spectral analysis provided consistent results. In particular, Raman bands in the high frequency region are sensitive to effects of different ZnO/BaO or BaF₂/BaO ratio on structure of glasses.     

Glasses and glass-ceramics in the oxyfluoride ternary system Pb(PO3)2-WO3-PbF2

Glasses were prepared by the melt-quenching method in the ternary system Pb(PO₃)₂-WO₃-PbF₂ and doped with Er³⁺ in order to prepare luminescent transparent glass-ceramics. This work focused on thermal and structural characterization of tungsten lead-phosphate glasses and crystallization study for preparing transparent glass-ceramics. Thermal properties such as thermal stability and crystallization behavior upon heating were investigated by DSC in function of PbF₂ content. For low PbF₂ concentrations, only one crystallization peak due to Pb₃(PO₄)₂ is observed whereas samples containing more than 15% of PbF₂ present another exothermic event at lower temperatures related with precipitation of PbF₂, Pb₂P₂O₇ and Pb₂OF₂. Structural investigations by Raman spectroscopy suggest that PbF₂ modifies the tungsten-phosphate network through the formation of P―F and P―O―Pb bonds but the average network connectivity remains almost constant. A crystallization study has been performed by DSC to investigate the dominant crystallization mechanisms in these glasses and it has been established that Pb₃(PO₄)₂ is nucleated on the surface whereas PbF₂, Pb₂P₂O₇ and Pb₂OF₂ crystallize dominantly from the glassy bulk. Transparent glass-ceramics containing nanosized PbF₂ crystallites were also prepared by suitable heat-treatment on the glass sample containing 20% of PbF₂ and Raman microscopy of these glass-ceramics supports the crystallization mechanisms determined by DSC.     

Lanthanum fluorozirconate glasses

Investigations in the ZrF₄-BaF₂-LaF₃ ternary system show the existence of a vitreous area in the range: ZrF₄: 56–67%, BaF₂:25–36%, LaF₃:3–13%. For a standard glass of molar composition 0.62 ZrF₄, 0.30 BaF₂, 0.08 LaF₃, the refractive index is 1.5248 with the glassy transition occuring at 310°C and fusion occuring at 545°C.Quaternary glasses have been obtained by including a MF fluoride (M = Na or Li) with the previous ternary glass according to the formula: (0.62 – 0.4x)ZrF₄(0.30 –0.5x)BaF₂(0.088 – 0.1x)LaF₃xMF. Evolution of glassy transition, refractive index, density and molar refractivity is discussed in relation to the structural role of the Na⁺ and Li⁺ ions. In these zirconium fluoride glasses, lithium could act as a network former at low concentration and as a network modifier at higher concentration.     

Quenched glasses containing lanthanum and other trivalent sulfates

A wide glass-forming region has been observed in the Li₂SO₄-La₂(SO₄)₃ system with essentially pure glass produced by roller quenching compositions of 20 to 90% Li. Even water or air quenching produced glasses. Many of these glasses showed double exotherms during crystallization and some showed glass transitions. Limited experiments also showed some glass-formation in other alkali-La sulfates, in compositions containing Y and Sc sulfates and in mixtures. Ionic conductivities and some infrared measurements are also reported.