Composition analysis of glasses in the PbBr2–PbCl2–PbF2–PbO–P2O5 system

Composition change during the melting process of some glasses in the PbBr₂–PbCl₂–PbF₂–PbO–P₂O₅ system melted at 450–470°C for 15 min was studied. Results show that there was a remarkable difference between the batch composition and the analyzed composition. Large amount of P, Br, Pb, and Cl were lost mainly in the form of PbBr₂, PbCl₂ and P₂O₅. The content of O is influenced by two factors. The incomplete decomposition of NH₄H₂PO₄ or the reaction between P₂O₅ and H₂O in the atmosphere increases the content of O, while the volatilization of P₂O₅ decreases the content of O.     

Characteristics and biocompatibility of Na2O–K2O–CaO–MgO–SrO–B2O3–P2O5 borophosphate glass fibers

A novel Na₂O–K₂O–CaO–MgO–SrO–B₂O₃–P₂O₅ borophosphate glass fiber is prepared. The thermal properties including differential thermal analysis (DTA) and viscosity measurement of the glass were presented. The tensile strength of the glass fiber is measured. The reaction of the glass fibers in the SBF solution is characterized by XRD, FTIR and SEM. XRD and FTIR indicate that the carbonate hydroxyapatite has formed rapidly on the glass. Cell attachment, spreading and proliferation on the glass are determined by MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide] assay method using Human osteosarcoma MG-63 cells. The bioactivity and biocompatibility of the glass fiber make it a good potential prospect in the field of tissue engineering.     

Raman and NMR study of bioactive Na2O–MgO–CaO–P2O5–SiO2 glasses

The results of a structural study combining NMR and Raman spectroscopy of several melt-derived glasses in the system Na₂O–MgO–CaO–P₂O₅–SiO₂ are presented. The Raman spectra show clear changes in the Si–O–Si vibrational modes (related to the bridging oxygen atoms, BO) and also verify the presence of non-bridging oxygen atoms (NBO), also named terminal oxygens. The intensity of the Si–O–NBO stretching mode depends on the cation concentration. It can be concluded from the NMR studies that the MgO-containing samples have orthophosphate units charge-compensated by Ca²⁺ and Mg²⁺. The silicate matrix also contains both types of two-valent cations and consists of Q² and Q¹ units. Similarly, the Na₂O-containing samples contain isolated orthophosphate units in a silicate matrix (Q² and Q³ units), both charge-compensated by mixed cations Ca²⁺ and Na⁺. These experimental data were compared with theoretical parameters given by the Stevels model, which is a suitable tool for understanding bioactive behavior of these glasses. Furthermore, results of the in vitro tests carried out in simulated body fluids are presented and compared with both Raman and NMR structural data.     

Optical properties of new low-phonon SnF2–PbF2–ZnF2 glasses

New fluoride glasses were developed in the SnF₂–PbF₂–ZnF₂ system. Additions of 5 mol% of CsCl or 6–15 mol% of AlF₃ were found to stabilize the glass formation. The IR absorption of the glasses and the optical properties of the europium ions doped in the glasses were compared with those of a fluorozirconate glass as a representative fluoride glass. The IR spectra showed that the new glasses have the peak of the phonon energy at 400 cm⁻¹, which is about 100 cm⁻¹ lower than that of the fluorozirconate glass. The results of the fluorescence measurement of the europium ions revealed that the multi-phonon relaxation rate in these glasses is smaller than that in the fluorozirconate glass.     

Second-order optical non-linearity initiated in Li2O–Nb2O5–SiO2 and Li2O–ZnO–Nb2O5–SiO2 glasses by formation of polar and centrosymmetric nanostructures

Amorphous nanoheterogeneities of the size less than 100 Å have been formed in glasses of the Li₂O–Nb₂O₅–SiO₂ (LNS) and Li₂O–ZnO–Nb₂O₅–SiO₂ (LZNS) systems at the initial stage of phase separation and examined by transmission electron microscopy, small-angle X-ray and neutron scattering. Both LNS and LZNS nanoheterogeneous glasses exhibit second harmonic generation (SHG) even when they are characterized by fully amorphous X-ray diffraction (XRD) patterns. Chemical differentiation and ordering of glass structure during heat treatments at appropriate temperatures higher T_g lead to drastic increase of SHG efficiency of LNS glasses contrary to LZNS ones in the frame of amorphous state of samples. Following heat treatments of nanostructured glasses result in crystallization of ferroelectric LiNbO₃ and non-polar LiZnNbO₄ in the LNS and LZNS glasses, respectively. Taking into account similar polarizability of atoms in LNS and LZNS glasses, the origin of the principal difference in the second-order optical non-linearity of amorphous LNS and LZNS samples is proposed to connect predominantly with the internal structure of formed nanoheterogeneities and with their polarity. Most probably, amorphous nanoheterogeneities in glasses may be characterized with crystal-like structure of polar (LiNbO₃) phase initiating remarkable SHG efficiency or non-polar (LiZnNbO₄) phase, which do not initiate SHG activity. It gives an opportunity to vary SHG efficiency of glasses in a wide rage without remarkable change of their transparency by chemical differentiation process at the initial stage of phase separation when growth of nanoheterogeneities is ‘frozen’. At higher temperatures, LiNbO₃ crystals identified by XRD precipitate in LNS glasses initiating even more increase of SHG efficiency but visually observable transparency is impaired.     

Formation of Co2+-doped nanocrystals in La2O3–MgO–Al2O3–SiO2 glass-ceramics

Transparent glass-ceramics were synthesized by heat-treatment of glass with a composition of 5La₂O₃–13.2MgO–28.8Al₂O₃–46SiO₂–4.5TiO₂–2.5ZrO₂–0.15CoO (LMAS) (wt.%). The activation energy of crystallization and the Avrami parameter for the LMAS glass were determined from the DTA curves at different heating rates. The most two intense bands of Raman spectrum of initial glass at ~ 810 cm^?1 and ~ 900 cm^?1 were connected with the presence of [SiO₄] and [TiO₄] tetrahedral, respectively. After heat-treated at 700 °C/10 h+820 °C/8 h, the intensity of the band for [TiO₄] tetrahedral weakened, while an intensive band at ~ 800 cm^?1 for the Ti–O bond appeared. Other bands were characteristics of high-silicate network and x(MgTi₂O₅)·y(Al₂TiO₅) polycrystals. The changes reflected phase separation after heat-treatment of the initial glass. The strong absorption band of glass-ceramics centered at 580 nm can be assigned to ⁴A₂(⁴F)→⁴T₁(⁴P) and the broad absorption band at 1100–1700 nm to ⁴A₂(⁴F)→⁴T₁(⁴F) transitions of tetrahedral coordinated Co²⁺ ion. Two broad emission bands, one was around 660 nm, the other was from 800 nm to 1050 nm, of glass-ceramics correspond to the ⁴T₁(⁴P)→⁴A₂(⁴F) and ⁴T₁(⁴P)→⁴T₂(⁴F) transitions of tetrahedral coordinated Co²⁺ ions. The absorption and emission features clearly demonstrated that Co²⁺ ions were incorporated into nanocrystals and located in tetrahedral sites.     

Spectroscopic properties of Co2+ ions in La2O3–MgO–Al2O3–SiO2 glass-ceramics

Co²⁺-doped La₂O₃–MgO–Al₂O₃–SiO₂ (LMAS) glass-ceramics was synthesized by conventional method. The microstructure of LMAS GCs heat-treated at 760 °C/12 h + 930 °C/4 h was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The spectroscopic properties of Co²⁺-doped LMAS GCs were studied by absorption spectrum, excitation spectrum, and temperature dependent luminescence spectra. XRD results revealed the sizes of MgAl₂O₄ crystalline phases are about 9.1 ± 1.5 nm. The three peaks in the visible absorption band of LMAS GCs at 549 nm, 585 nm and 626 nm are connected with the transitions from ⁴A₂ level to ²A₁/²T₂(²G), ⁴T₁(⁴P) and ²E/²T₁(²G) levels, respectively, and excitations into them emit the radiation at around 666 nm. The luminescence intensity increased with temperature increasing from 10 K to 150 K, while it weakened with temperature increasing from 150 K to 350 K. These features were explained by the effects of two competing mechanisms.     

The effect of TiO2 on phase separation and crystallization of glass-ceramics in CaO–MgO–Al2O3–SiO2–Na2O system

The experiments were carried out on studying the effect of phase separation on nucleation and crystallization in the glass based on the system of CaO–MgO–Al₂O₃–SiO₂–Na₂O. In the experiments, TiO₂ was chosen as nucleating agent. Three batches of 5, 8 and 10 wt% TiO₂ substitution were investigated by the techniques of DSC, XRD, FTIR and FESEM equipped with EDS. XRD and FTIR analysis indicated that the super cooled glasses were all amorphous, the heat treatment leading to nucleation would cause a disruption of silica network which followed phase separation. The phase separation followed the generation of crystal seeds Mg(Ti, Al)₂O₆. FESEM observation and EDS analysis revealed that the more TiO₂ content of glass, the more droplet separated phase and crystal seeds after nucleation heat treatment. The main crystal phase is clinopyroxene, Ca(Ti, Mg, Al)(Al, Si)O₆, of crystallized glass.     

Magnetite nanoparticles prepared by the crystallization of Na2O–Fe2O3–B2O3–SiO2 glasses

A glass with the composition of 35Na₂O–24Fe₂O₃–20B₂O₃–20SiO₂–1ZnO (mol%) was melted, quenched, using a twin roller technique, and subsequently heat treated in the range 485–750 °C for 1–2 h. This led to the crystallization of magnetite as the sole or the major crystalline phase.Heat treatment at lower temperatures resulted in the crystallization of magnetite crystals 7–20 nm in diameter, whereas heat treatment at higher temperatures produced higher quantities of magnetite and much larger crystals. The room temperature magnetization and coercive force values were in the range of 6–57 emu g^? 1 and 0–120 Oe, respectively for the heat treated glasses.     

EXAFS study of the Er3+ ion coordination in SiO2–TiO2–HfO2 sol–gel films

The local order around ion-implanted Er³⁺ ions in SiO₂–TiO₂–HfO₂ thin films prepared by sol–gel, was studied by extended X-ray absorption fine structure at the Er-L_III edge. Both the first and second coordination shells of Er³⁺ were analyzed for different heat-treatments. While the first coordination shell always consisted of ～6–7 oxygen atoms at distances varying between 2.23 and 2.27 Å, the structure of the second shell was found to vary with the film composition and heat-treatment. Namely, whereas Si was found to be the only second neighbor of erbium in binary SiO₂–TiO₂ films, the addition of HfO₂ caused a preferential replacement of Si by Hf. The post-implantation thermal treatments also played a fundamental role in determining the final environment of the erbium ions.     

Electrical and dielectric properties of MnF2–ZnF2–NaPO3 glasses

Direct electrical conductivity and dependencies of complex electrical modulus vs. temperature and frequency have been measured on glasses from the MnF₂–ZnF₂–NaPO₃ system. These glasses are sensitive to atmospheric humidity and as a consequence, the electrical conductivity increases up to temperature of 50 °C. A hydrated layer is created by the effect of water and leads to the significant increase of the electrical conductivity in the case of 0MnF₂–20ZnF₂–80NaPO₃ glass. This behavior is governed by Arrhenius relation where the values of activation energy are increasing and values of the electrical conductivity are decreasing with the amount of MnF₂. Dielectric measurements show that a heterogeneous phase is formed in the bulk of glasses. This may be seen when plotting complex electrical modulus in the complex plane. The records made by the light microscope confirmed the occurrence of the other phase in the bulk of glasses.     

Piezoelectric and elastic properties of ZnF2–PbO–TeO2: TiO2 glass ceramics

Piezoelectric coefficients d₃₃ as well as ultrasonic velocities and elastic coefficients of ZnF₂–PbO–TeO₂ glasses crystallized with different concentrations of TiO₂ (0.5 to 2.0 wt.%) were measured. The contribution to the piezoelectric coefficients is attributed to presence of Pb₅Ti₃F₁₉, PbTiO₃ and PbTeO₃ ferroelectric crystal phases. The piezoelectric coefficients show substantial sensitivity to presence of TiO₂. The ultrasonic velocities and the related elastic coefficients in these glass ceramics as a functions of concentration of nucleating agent TiO₂ exhibited minimal effect at 1.0 wt.%. This is ascribed to the larger presence of titanium ions in Ti³⁺ states which act as modifiers and finally de-polymerize glass ceramic network. The results have been further discussed quantitatively within a framework of different oxidation states of titanium ions and the nature of the crystal phases ingrained in the glass ceramic.     

Studies of ternary Li2SO4–Li2O–P2O5 glasses

Glasses in a wide range of compositions in the ternary system xLi₂SO₄–yLi₂O–zP₂O₅ where x ranges from 0 to 30 mol%, y ranges from 35 to 55 mol% and z ranges from 25 to 50 mol% have been prepared and their properties measured using infra-red, Raman, and ³¹P magic angle spinning nuclear magnetic resonance spectroscopic techniques. We conclude that a random close packing of phosphate and sulphate ions which also leads to formation of connected voids in the structure is consistent with our data. There is also evidence for formation of condensed sulphate–phosphate species in the liquid which may be retained in the glass structure.     

Spectroscopic studies of tungsten ions in PbO–PbF2–SiO2 glasses

40PbO–(10 ? x)PbF₂–50 SiO₂:xWO₃ (where x = 1 to 7 mol%) glasses are prepared in the glass forming region. Spectroscopic studies (UV–Vis absorption, ESR, IR) are carried out for these glasses. Interesting changes are observed in the spectroscopic parameters of these glasses when the concentration of WO₃ is changing in the glass matrix. Two absorption bands are observed around at 830 and 620 nm. ESR signal are measured at room temperature for these glasses, the strength of the signal is increased and hyperfine splitting is resolved with increasing the concentration of WO₃ in the glass matrix. IR transmission gives valuable information about the nature of bonds in the glass matrix. The physical parameters along with spectroscopic parameters are measured.     

Effect of TiO2 addition on the chemical durability of Bi2O3–SiO2–ZnO–B2O3 glass system

The effect of the substitution of ZnO for TiO₂ on the chemical durability of Bi₂O₃–SiO₂–ZnO–B₂O₃ glass coatings in hot acidic medium (0.1 N H₂SO₄ at 80 °C) for different times was studied. The thick films produced by a screen-printing method and heat treated at 700 °C/5 min were analyzed by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The glass from the Bi₂O₃–SiO₂–ZnO–B₂O₃ system developed Zn₂SiO₄ and a glassy phase that were readily attacked by hot 0.1 N sulfuric acid, whereas the heat treated coating from the Bi₂O₃–SiO₂–TiO₂–ZnO–B₂O₃ system presented a finer microstructure with thin interconnected Bi₄Ti₃O₁₂ crystals and a glassy phase more resistant to hot 0.1 N sulfuric acid attack etching.     

Structure and properties of NaPO3–ZnO–Nb2O5–Al2O3 glasses

In an effort to design low-melting, durable, transparent glasses, two series of glasses have been prepared in the NaPO₃–ZnO–Nb₂O₅–Al₂O₃ system with ZnO/Nb₂O₅ ratio of 2 and 1. The addition of ZnO and Nb₂O₅ to the sodium aluminophosphate matrix yields a linear increase of properties such as glass transition temperature, density, refractive index and elastic moduli. The chemical durability is also significantly, but nonlinearly, improved. The glass with the highest niobium concentration, 55NaPO₃–20ZnO–20Nb₂O₅–5Al₂O₃ was found to have a dissolution rate of 4.5 × 10^? 8 g cm^? 2 min^? 1, comparable to window glass. Structural models of the glasses were developed using Raman spectroscopy and nuclear magnetic resonance spectroscopy, and the models were correlated with the compositional dependence of the properties.     

Spectral investigations on VO2+ ion doped in CaO–SrO–Na2O–B2O3 glass systems

Glasses of the (20 ? x)CaO–xSrO–(20 ? y)Na₂O–60B₂O₃ ? y (CSNB) system with (5 ≤ x ≤ 15) mol% and y = 0.1 mol% of V₂O₅ were characterized by X-ray diffraction (XRD), EPR (Electron Paramagnetic Resonance), Optical absorption Spectra and FT-IR (Fourier transform Infrared Spectroscopy) studies. EPR spectra of all the glass samples exhibit resonance signals characterstic of VO²⁺ ions. The values of spin-Hamiltonian parameters indicate that the VO²⁺ ions in CSNB glasses were present in octahedral sites with tetragonal compression and belong to C_4v symmetry. Spin-Hamiltonian parameters ‘g’ and ‘A’ were evaluated. The Optical band energy (E_opt) and Urbach energy (ΔE) were calculated from their ultra violet edges. By correlating EPR and Optical data the molecular orbital coefficients have been evaluated. IR spectra of these glasses were analyzed in order to identify the contribution of each component to the local structure that determines the physical properties of these glasses.     

Structural role and coordination environment of Fe in Fe2O3–PbO–SiO2–Na2O composite glasses

The structural role, coordination geometry and valence of Fe in a series of Fe₂O₃–PbO–SiO₂–Na₂O glasses are studied by means of Fe-K-NEXAFS and EXAFS spectroscopies. Parameters for the study are the concentration of the Fe and Pb-oxides, the SiO₂/Na₂O ratio and the cast temperature. The EXAFS and NEXAFS results reveal that the role of Fe³⁺ depends on the concentration of Fe₂O₃. More specifically, in most of the studied quaternary systems, the Fe³⁺ ion is a glass former, i.e. the Fe atoms belong to FeO₄ tetrahedra that participate in the formation of the glassy network. The role of Fe as an intermediate oxide is identified only in one sample with 20 wt% Fe₂O₃, where ～80 at.% of the Fe atoms are tetrahedrally coordinated with O atoms, while the remaining ～20 at.% of the Fe atoms occupy octahedral sites. It is also revealed that the tetrahedral coordination of Fe in the vitreous matrix is destroyed when a number of parameters is altered, such as the T_cast, the (Fe + Si)/O and the SiO₂/Na₂O ratio.     

BaO–B2O3–SiO2–Al2O3 sealing glass for intermediate temperature solid oxide fuel cell

Glasses in the formulation close to BaSiO₃–BaB₂O₄ eutectic compound are developed for sealing of intermediate-temperature (500–650 °C) solid oxide fuel cell (IT-SOFC). Thermal and microstructural analyses of the glasses with 0–10 mol% Al₂O₃ are also conducted. Detailed crystallization kinetics and interfacial stability of the glass in contact with yttria-stabilized zirconia (YSZ) and samaria-doped ceria (SDC) are investigated and compared. The results show that the formulation, 47BaO–21B₂O₃–27SiO₂–5Al₂O₃ (G1A5), performs the best on glass forming ability (GFA) among all tested formulations, and shows matched thermal expansion and working temperature to CeO₂-based electrolytes of IT-SOFC. Two major crystalline phases that precipitate from G1A5 above 750 °C are platy hexacelsian and BaSiO₃ grains.     

Ion conductive chalcohalide glasses in LiI–Ga2S3–GeS2 system

The electric properties of LiI containing chalcohalide glasses in the system Ga₂S₃–GeS₂ were studied by means of impedance spectroscopy and potentiostatic chronoamperometry. Two sets of the samples were prepared by direct synthesis from elements and compounds in evacuated quartz ampoules. The prepared glasses were as follows: xLiI–xGa₂S₃–(100?2x)GeS₂, x = 15, 20, 25 and 20LiI–xGa₂S₃–(80?x)GeS₂, x = 0, 5, 10, 15 and 20. In the first set the concentration of LiI increased and the second set was prepared to study the influence of Ga₂S₃ on the properties of the glasses. Additional aim of this work was to compare the electric properties of LiI containing Ga₂S₃–GeS₂ glasses with analogous AgI containing Ga₂S₃–GeS₂ glasses recently studied by us. The conductivity of the LiI containing glasses in the Ga₂S₃–GeS₂ system was higher and the activation energy was lower than in the analogous AgI containing system. The residual electronic (hole) conductivity remained similar in both systems being almost negligibly low. Raman spectroscopy proved the influence of LiI as well as Ga₂S₃ on glass structure, however interpretation of Raman spectra of these glasses is complicated due to small mass difference between gallium and germanium.