Fabrication and properties of novel low-melting glasses in the ternary system ZnO-Sb2O3-P2O5

Glasses in the ternary system ZnO-Sb₂O₃-P₂O₅ were investigated as potential alternatives to lead based glasses for low temperature applications. The glass-forming region of ZnO-Sb₂O₃-P₂O₅ system has been determined. Structure and properties of the glasses with the composition (60 − x)ZnO-xSb₂O₃-40P₂O₅ were characterized by infrared spectra (IR), differential thermal analysis (DTA) and X-ray diffraction (XRD). The results of IR indicated the role of Sb³⁺ as participant in glass network structure, which was supported by the monotonic and remarkable increase of density (ρ) and molar volume (V_M) with increasing Sb₂O₃ content. Glass transition temperature (T_g) and thermal stability decreased, and coefficient of thermal expansion (α) increased with the substitution of Sb₂O₃ for ZnO in the range of 0-50 mol%. XRD pattern of the heat treated glass containing 30 mol% Sb₂O₃ indicated that the structure of antimony-phosphate becomes dominant. The improved water durability of these glasses is consistent with the replacement of easily hydrated phosphate chains by corrosion resistant P-O-Sb bonds. The glasses containing ?30 mol% Sb₂O₃ possess lower T_g (<400 °C) and better water durability, which could be alternatives to lead based glasses for practical applications with further composition improvement.     

Remark on the optical gap in ZnO-Bi2O3-TeO2 glasses

Four ZnO-Bi₂O₃-TeO₂ glasses were prepared from high purity (4N5) oxides. From measurements of the optical transmission on very thin bulk samples the optical gap was determined at around 3.55 eV for the glasses studied. The temperature dependence of the optical gap was also determined from the room temperature close up to 500 K. Preliminary Raman scattering measurements indicate that with a decrease in TeO₂ content, TeO₄ trigonal bipyramid transformation proceeds into TeO₃ trigonal pyramids.     

Spectroscopic properties of Er-doped Na2O-Sb2O3-B2O3-SiO2 glasses

Spectroscopic properties of Er³⁺-doped Na₂O-Sb₂O₃-B₂O₃-SiO₂ glasses have been investigated for developing 1.5-μm broadband fiber amplifiers. An intense 1.5-μm near infrared emission with a broad full width at half maximum (FWHM) of 88 nm has been obtained for Er³⁺-doped 5Na₂O-20Sb₂O₃-35B₂O₃-40SiO₂ glass upon excitation with a 980 nm laser diode. The obtained emission cross-section of the ⁴I_13/2 → ⁴I_15/2 transition and the lifetime of the ⁴I_13/2 level of Er³⁺ ions are 6.8 × 10⁻²¹ cm² and 0.36 ms, respectively. It is noted that the product of the emission cross-section and the FWHM of the glass, σ_e × FWHM, is as great as 598.4 × 10⁻²¹ cm² nm, which is comparable or higher than that of Er³⁺-doped bismuth-based and tellurite-based glasses. These special optical properties encourage in identifying them as important materials for potential applications in high performance optics and optical communication networks.     

Orthophosphate nanostructures in SiO2-P2O5-CaO-Na2O-MgO bioactive glasses

Vibrational spectroscopy, ²⁹Si and ³¹P magic-angle spinning nuclear magnetic resonance spectroscopy and high resolution transmission electron microscopy were used to investigate structural aspects of SiO₂-P₂O₅-CaO-Na₂O-MgO glasses. The experimental results show that for the two compositions, 25.3SiO₂-10.9P₂O₅-32.6CaO-31.2MgO and 33.6SiO₂-6.40P₂O₅-19.0CaO-41.0MgO, phosphorous is present in a nano-crystalline form with interplanar distances in the 0.21-0.26 nm range. The two glasses develop a surface CaP-rich layer and the presence of any intermediate silica-rich layer was not detected. It was suggested that the phosphate nano-regions may play a key role in the initial stages of the bioactive process, acting as nucleation sites for the calcium phosphate-rich layer.     

Phase separation and crystallization in the system SiO2-Al2O3-P2O5-B2O3-Na2O glasses

The phase separation and crystallization behavior in the system (80 − X)SiO₂ · X(Al₂O₃ + P₂O₅) · 5B₂O₃ · 15Na₂O (mol%) glasses was investigated. Glasses with X = 20 and 30 phase separated into two phases, one of which is rich in Al₂O₃-P₂O₅-SiO₂ and forms a continuous phase. Glasses containing a larger amount of Al₂O₃-P₂O₅ (X = 40 and 50) readily crystallize and precipitates tridymite type AlPO₄ crystals. It is estimated that the phase separation occurs forming continuous Al₂O₃-P₂O₅-SiO₂ phase at first, and then tridymite type AlPO₄ crystals precipitate and grow in this phase. Highly transparent glass-ceramics comparable to glass can be successfully obtained by controlling heat treatment precisely. The crystal size and percent crystallinity of these transparent glass-ceramics are 20-30 nm and about 50%, respectively.     

Optical properties of and concentration quenching in Bi2O3-B2O3-Ga2O3 glasses

Er₂O₃-doped Bi₂O₃-B₂O₃-Ga₂O₃ glasses were prepared by the conventional melt-quenching method, and the Er³⁺:⁴I_13/2 → ⁴I_15/2 fluorescence properties are studied for different Er³⁺ concentrations. when the Er₂O₃ concentration increases from 0.03 to 3.0 mol%, the measured lifetime of Er³⁺:⁴I_13/2 level decrease from 2.24 to 0.9 m s, and from 0.25 to 0.20 m s for the Er³⁺:⁴I_11/2 level. The fast energy migration among Er³⁺ ions cause the reduction of lifetime of the ⁴I_13/2 level, whereas the change in the ⁴I_11/2 level is mainly due to a cooperative upconversion process (⁴I_11/2, ⁴I_11/2) → (⁴F_7/2, ⁴I_15/2). Based on the dipole-dipole interaction theory, the interaction parameter, C_Er,Er, for the migration rate of Er³⁺:⁴I_13/2 ↔ ⁴I_13/2 was calculated to be 32 × 10⁻⁴⁰ cm⁶ s⁻¹.     

Physicochemical studies of phosphate based P2O5-Na2O-CaO-TiO2 glasses for biomedical applications

Glasses P₂O₅-Na₂O-CaO-TiO₂ with different TiO₂ contents and fixed P₂O₅ (45 wt%) and CaO (24 wt%) have been prepared employing the normal melting and annealing technique. Measurements such as ultrasonic velocity, attenuation, solubility and pH have been carried out in all the compositions of the glasses. It is interesting to note that the above measured ultrasonic parameters exhibit an abnormal behavior (minimum) at 0.5 wt% of TiO₂ content, beyond which an increase in these parameters with increasing TiO₂ content is observed. The maximum pH values and Ca²⁺ ion release have been observed for the TiO₂ free glass those compositions with and the low TiO₂(?1.0 wt%) content. As the content of the TiO₂ increases, the solubility of the glasses decreases. The observed weight loss reveals two stages of phosphate dissolution kinetics i.e. the first stage, in which the weight loss is proportional to t^1/2, and a second stage in which a linear behavior is observed.     

A study of nonlinear optical properties in Bi2O3-WO3-TeO2 glasses

A series of bismuth tungsten tellurite glasses were prepared and their densities, linear refractive indices and transmission spectra were measured. The optical bandgaps E_opt and Urbach energies E_e of glasses were obtained from ultraviolet absorption edges. Both the optical gap (E_opt) and the band tail (E_e) are behaving oppositely. As the value of E_opt decreases with increasing WO₃ content, the degree of disorder increases which causes more defects or localized states resulting in deep localized in the bandgap with the tailing increased. Z-scan technique was carried out to investigate the third-order nonlinear optical properties of Bi₂O₃-WO₃-TeO₂ glasses. The third-order optical nonlinearity increases with decreasing the optical bandgap E_opt, since a increase of WO₃ content can provide the non-bridging oxygen ion content.     

Effect of BaO content on the sintering and physical properties of BaO-B2O3-SiO2 glasses

A BaO-B₂O₃-SiO₂ glass system was chosen as a candidate composition for the application to Pb-free low temperature sinterable glass. The effect of BaO content on the crystallization, sintering behavior, and properties of the glasses was examined. Both the glass transition temperature and crystallization temperature decreased as the BaO content increased. Crystallization easily occurred during sintering with a BaO content of more than 50 mol%, which effectively inhibited the over-firing phenomenon. The dielectric characteristics and thermal expansion coefficient of the glasses were examined and the results were explained on the basis of the crystallization and densification of the specimens.     

Thermo-optic properties of B2O3 doped Li2O-Al2O3-SiO2 glass-ceramics

Reduction in the temperature coefficient of the optical path length, dS/dT of Li₂O-Al₂O₃-SiO₂ glass-ceramics with near-zero thermal expansion coefficient was attempted using control of the temperature coefficient of electronic polarizability, ?, and the thermal expansion coefficient, α. The dS/dT value of 2.6 mol% B₂O₃-doped glass-ceramic was 12.5  × 10⁻⁶/°C, which was 0.9 ×  10⁻⁶/°C smaller than that of B₂O₃-free glass-ceramic. On the other hand, reduction in dS/dT through B₂O₃ doping was not confirmed in precursor glasses. Results showed that reduction in dS/dT of the glass-ceramic through B₂O₃ doping is caused by the reduction in ?. The reduction in ? from B₂O₃ doping was probably attributable to numerical reduction in non-bridging oxide ions with larger ? value by the concentration of boron ions in the residual glass phase. In addition, application of hydrostatic pressure during crystallization was effective to inhibit precipitation of β-spodumene solid solution, which thereby decreases dS/dT. The dS/dT value of B₂O₃-doped glass-ceramic crystallized under 196 MPa was 11.7 ×  10⁻⁶/°C. That value was slightly larger than that of silica glass. The α value of this glass-ceramic was smaller than that of silica glass.     

Crystallization kinetics of Fe73.5−xMnxCu1Nb3Si13.5B9 (x = 0, 1, 3, 5, 7) amorphous alloys

In this study, we have investigated the effect of substituting Mn for Fe on the crystallization kinetics of amorphous Fe_73.5−xMn_xCu₁Nb₃Si_13.5B₉ (x = 1, 3, 5, 7) alloys. The samples were annealed at 550 °C and 600 °C for 1 h under an argon atmosphere. The X-ray diffraction analyses showed only a crystalline peak belonging to the α-Fe(Si) phase, with the grain size ranging from 12.2 nm for x = 0 to 16.7 nm for x = 7. The activation energies of the alloys were calculated using Kissinger, Ozawa and Augis-Bennett models based on differential thermal analysis data. The Avrami exponent n was calculated from the Johnson-Mehl-Avrami equation. The activation energy increased up to x = 3, then decreased with increasing Mn content. The values of the Avrami exponent showed that the crystallization is typical diffusion-controlled three-dimensional growth at a constant nucleation rate.     

Crystal growth and characterization of two-leg spin ladder compounds: Sr14Cu24O41 and Sr2Ca12Cu24O41

Single crystals of Sr_14−xCa_xCu₂₄O₄₁ (x=0 and 12) are grown by the travelling solvent floating zone technique using an image furnace. The grown crystals are characterized for their single crystallinity by the X-ray and Neutron Laue method. The magnetic susceptibility measurements in Sr₁₄Cu₂₄O₄₁ show considerable anisotropy along the main crystallographic axes. Low-temperature specific heat measurement and DC susceptibility measurement in Ca-doped crystal showed antiferromagnetic ordering at 2.8 K at ambient pressure. High-pressure AC susceptibility measurement on Ca-doped crystal showed a sharp superconducting transition at 2 K under 40 kbars. T_c onset reached a maximum value of 9.9 K at 54 kbars. The bulk superconductivity of the sample is confirmed by the high-pressure AC calorimetry with T_c max=9.4 K and T_N=5 K at 56 kbars.     

Solubility of glasses in the system P2O5-CaO-MgO-Na2O-TiO2: Experimental and modeling using artificial neural networks

Phosphate glasses in the system P₂O₅-CaO-MgO-Na₂O-TiO₂ for use as degradable implant materials were produced. In order to classify their solubility behavior, dissolution experiments were performed in deionized water for 60 min at 98 °C. Resulting solutions were analyzed using ICP-OES. In addition, pH measurements were carried out in physiological NaCl solution. With increasing phosphorus oxide content, the glasses showed a higher solubility and gave lower pH values in aqueous solution. This was caused by changes in the glass structure, as long phosphate chains are more susceptible to hydration than smaller phosphate groups. These changes in glass structure were followed by ³¹P MAS-NMR experiments. Increasing sodium oxide concentrations in exchange for calcium or magnesium oxide also increased the glass solubility by disrupting ionic cross links between chains. By contrast, addition of titania made the glasses more stable towards dissolution by cross linking smaller phosphate groups. The aim of this study was to find a relationship between glass composition and solubility behavior. As classical linear methods of data analysis were unsuitable due to the complexity of the relationship, preliminary artificial neural networks analyses were performed and were found to be an interesting tool for modeling the solubility behavior of phosphate glasses.     

Structural study of PbO-MoO3-P2O5 glasses by Raman and NMR spectroscopy

Glasses in the ternary system PbO-MoO₃-P₂O₅ were prepared in three compositional series (100 − x)[0.5PbO-0.5P₂O₅]-xMoO₃ (A), 50PbO-yMoO₃-(50 − y)P₂O₅ (B) and (50 − z)PbO-xMoO₃-50P₂O₅ (C) and their structure was studied by Raman and ³¹P NMR spectroscopies. In the compositional series (100 − x)[0.5PbO-0.5P₂O₅]-xMoO₃ homogeneous glasses were prepared in the concentration region of 0-70 mol% MoO₃. Their glass transition temperature increases with increasing MoO₃ content having a maximum at x = 50 mol% MoO₃. ³¹P MAS NMR spectra reveal that in the glass series (A) the incorporation of MoO₃ results in the shortening of phosphate chains and gradual transformation Q² units into Q² and Q⁰ units, prevailing in glasses with a high MoO₃ content. Octahedral structural units MoO₆ dominate in most glass compositions and they are present also in the structure of Pb(MoO₂)₂(PO₄)₂ compound corresponding to the glass composition 50Pb(PO₃)₂-50MoO₃. The analysis of Raman spectra of glasses of the (B) series with a high MoO₃ content showed the transformation of octahedral MoO₆ units into tetrahedral MoO₄ units.     

Sodium tracer diffusion in glasses of the type (CaO·Al2O3)x(2 SiO2)1−x

Tracer diffusion coefficients of the radioactive isotope Na-22 were measured in glasses of the type (CaO·Al₂O₃)_x(2 SiO₂)_1−x to study the diffusion of sodium as a function of glass composition, x, temperature and initial water content. The diffusion of Na-22 in glasses diffusion-annealed in dry air can always be well described by a single tracer diffusion coefficient, but sometimes not in samples annealed in common air. It was found that the sodium tracer diffusion coefficient decreases by about six orders of magnitude when the glass composition x changes from 0 to 0.75 at 800 °C. The temperature dependence of the diffusion of sodium seems to decrease as the silica content increases. Variations of the initial water content in some of the glasses investigated did not very significantly influence the rate of the tracer diffusion of sodium.     

O nuclear magnetic resonance study of Na2O-P2O5 glasses

The preparation and structural investigation of ¹⁷O-enriched xNa₂O-(100−x)P₂O₅ glasses (46.5?x?62.8) by nuclear magnetic resonance (NMR) is described. Enriched phosphoric acid was prepared by hydrolysis of PCl₅ with ¹⁷O-enriched water and neutralized with sodium carbonate. The sodium metaphosphate was then melted at 800 °C for 15 h and quenched. Polyphosphate and ultraphosphate glass compositions were prepared by remelting the metaphosphate with sodium carbonate and phosphorus pentoxide, respectively. ³¹P magic angle sample spinning (MAS) NMR was used to determine the Na₂O/P₂O₅ content in the glasses. ¹⁷O NMR spectra (quadrupole echo for non-rotating samples and multiple-quantum excitation for rotating samples (MQMAS)) show two oxygen sites in the samples with large quadrupolar coupling constants (4.7 and 7.7 MHz), in accordance with the high phosphorus electronegativity. According to the correlation of ¹⁷O quadrupolar constants with bond ionicity, these two components are attributed to bridging P-O-P and non-bridging P-O?Na oxygens. The average P-O-P bond angle is estimated with the quadrupolar asymmetry derived from the fit of the static echo spectra. The MQMAS spectrum shows a distribution of non-bridging oxygen chemical shifts, attributed to a variation of bond length and angle.     

Sulfur behavior in silicate glasses and melts: Implications for sulfate incorporation in nuclear waste glasses as a function of alkali cation and V2O5 content

The presence of sulfur in radioactive waste to be incorporated in borosilicate glasses entails difficulties mainly due to the relatively low solubility of sulfates in the vitreous phase. In this work a study is presented on the effects of the ratio R = [Na₂O]/[B₂O₃], the type of sulfate added and the addition of V₂O₅ on the incorporation of sulfates in borosilicate glasses. Glass samples were prepared at the laboratory scale (up to 50-100 g) by melting oxide and sulfate powders under air in Pt/Au crucibles. XRF and ICP/AES chemical analysis, SEM/EDS, microprobe WDS and Raman spectroscopy were employed to characterize the fabricated samples. The main experimental results confirm that the incorporation of sulfates in borosilicate glasses is favored by the network depolymerization, which evolves with the ratio R. The addition of V₂O₅ seems to accelerate the kinetics of sulfur incorporation in the glass and, probably, increase the sulfate solubility by modifying the borate network and fostering the formation of voids of shape and size compatible with the sulfur coordination polyhedron in the glassy network. The kinetics of X₂SO₄ incorporation in the glass seems to be slower when X = Cs.     

Effect of P2O5 on the early stage crystallization of K-fluorrichterite glass-ceramics

The addition of 2 mol% P₂O₅ to stoichiometric K-fluorrichterite (KNaCaMg₅Si₈O₂₂F₂, KFR) has been reported to enhance the mechanical properties and improve the in vitro biocompatibility of this glass-ceramic by promoting the formation of enstatite and fluorapatite (FA). Here, the effect of further increasing the P₂O₅ concentration on phase evolution of KFR has been investigated. XRD data showed that mica crystallized in samples with 4 and 5 mol% P₂O₅ (GP4 and GP5, respectively) at 650 °C, but no diopside was detected at higher temperatures, in contrast with the general phase evolution in KFR based glass-ceramics. More importantly, however, the addition of ?4 mol% P₂O₅ induced phase separation of the glass into a silica glass matrix and phosphate rich droplets prior to crystallization. EDS traces taken from samples heat-treated at 600 °C, revealed that the silica glass matrix was deficient in Mg and unlikely to be the host for crystallization of mica. Conversely, the P₂O₅ rich regions contained excess Mg and were considered to be the host for the formation of mica and FA.     

Effect of the annealing process on the microstructure of La2Zr2O7 thin layers epitaxially grown on LaAlO3 by metalorganic decomposition

La₂Zr₂O₇ (LZO) films have been grown by metalorganic decomposition (MOD) to be used as buffer layers for coated conductors. A characteristic feature of LZO thin films deposited by MOD is the formation of nanovoids in an almost single crystal structure of LZO pyrochlore phase. Annealing parameters (heating ramp, temperature, pressure, etc.) were varied to establish their influence on the microstructure of the LZO layers. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for sample characterization. The epitaxial pyrochlore phase was obtained for annealing temperatures higher than 850 °C whatever the other annealing conditions. However, the film microstructure, in particular, nanovoids shape and size, is strongly dependent on heating ramp and pressure during annealing. When using low heating ramp, percolation of voids creates diffusion channels for oxygen which are detrimental for the substrate protection during coated conductor fabrication. From this point of view high heating rates are more adapted to the growth of LZO layers.     

Study on the growth and interfacial strain of CoFe2O4/BaTiO3 bilayer films

CoFe₂O₄/BaTiO₃ bilayer films were epitaxially deposited on SrTiO₃ substrates by laser molecular beam epitaxy (LMBE). The growth process of the bilayer films was in-situ monitored by reflection high-energy electron diffraction (RHEED). Sixty nanometer thick-BTO layer was firstly fabricated in a layer-by-layer growth mode with an atomic smooth surface. CFO films with a varying thickness ranging from 5 to 60 nm were subsequently deposited on BTO-coated STO substrates. The different growth behaviors of CFO films were observed due to the lattice mismatch strain. Between two short stages of the growth mode transforming, a long duration with Stransky and Krastonov growth mode was maintained. Strainfully relaxed CFO film in the island growth mode was finally formed. High-resolution X-ray diffraction (HRXRD) was used to further analyze the strain effect. It was found that the tensile stress imposed on BTO by CFO was strengthened with increasing the thickness of CFO films, which could lessen the distortion of BTO by counteracting the compressive stress caused by STO substrates. The strengthened tensile stress weakened the ferroelectric property of BTO films by reducing structural tetragonality, which was demonstrated by polarization-electric (P-E) measurement.