Estimated immiscibility isotherms of the Li2O-Al2O3-SiO2 system

Using the immiscibility temperature estimation method, recently developed by the present author and Tomozawa, immiscibility isotherms of the Li₂O-Al₂O₃-SiO₂ system were estimated. High reliability of the estimated immiscibility isotherms was confirmed by observing the morphologies of phase-separated glasses, and also by comparing the estimated and observed immiscibility temperatures at several compositions. The determined immiscibility isotherms revealed that, in the Li₂O-Al₂O₃-SiO₂ system, only composition regions near the Li₂O-SiO₂ and Al₂O₃-SiO₂ binary edges are phase-separable. In composition regions where base glasses for commercial glass-ceramics are located, the immiscibility temperatures were much lower than the glass transition temperatures, implying that no phase separation actually occurs. Accordingly the phase separation in practical glasses for producing glass-ceramics may be attributed to increased immiscibility resulting from various additives.     

Glass formation in the system CaO-Al2O3-CaF2

The formation of glass in the system CaO-Al₂O₃-CaF₂ has been investigated in sealed platinum capsules having about one atmosphere pressure of AlF₃ vapour. Transparent colourless glass could be obtained in the low-fluoride moderate-alumina region of the system (Al₂O₃ 35 to 60%, CaF₂ 0 to 20%). With the concentration of CaF₂ exceeding 20% considerable amount of quench crystals of CaF₂ appeared in the glass. Moderate-alumina low-lime melts containing more than 35% CaF₂ occur in an immiscibility zone. At the low-fluoride periphery of the liquid immiscibility zone a small zone of metastable liquid immiscibility has been found. The results of electron microscopic and infra-red spectroscopic studies of a few selected glasses have been analysed in combination with the molar refractivity data to reflect upon the co-ordination characteristics of aluminium in these glasses.     

Metastable liquid immiscibility and Vycor-type glass in phosphate-silicate systems

Glass formation and metastable liquid immiscibility in Na₂O-P₂O₅-SiO₂ glasses were studied. Phase separation in some of these glasses resulted in formation of an interconnected two-phase amorphous structure, similar to that in glasses of the Na₂O-B₂O₃-SiO₂ system used for production of Vycor glass. Leaching of the high-phosphate phase yielded a high-silica (over 90% SiO₂) skeleton, which could be sintered to a bulk glass.     

Crystallization kinetics and thermal properties of 20Li2O-80TeO2 glass

In this work, X-ray diffraction, Raman spectroscopy and differential scanning calorimetry techniques were used to understand the crystallization process on 20Li₂O-80TeO₂ glass. X-ray diffraction results reveal the presence of three distinct alpha γ-TeO₂, α-TeO₂ and α-Li₂Te₂O₅ crystalline phases in the glass matrix. The Raman spectroscopy band structure of this glass is similar to the one observed in glassy TeO₂. Raman results clearly reveal the metastable character of the γ-TeO₂ phase in the 20Li₂O-80TeO₂ glass, whose associated vibration modes disappear completely at temperatures higher than 315 °C. On the other hand, the Raman modes associated to α-TeO₂ and α-Li₂Te₂O₅ phases persists up to temperatures close to the final stages of the crystallization in the studied glass (around 420 °C). From DSC measurements, the activation energies 296 ± 3 and 298 ± 1 kJ mol⁻¹ were associated to γ-TeO₂ and α-TeO₂ phases crystallization, indicating that these phases crystallizes at temperatures very close in the studied glass.     

Preparation of B2O3-P2O5-SiO2 coating films by the sol-gel method

ThexB₂O₃ · (20-x) P₂O₅ · 80SiO₂ (in mol%) glass films withx=0, 10 and 20 have been prepared from metal alkoxides by carrying out the coating in a dry atmosphere. These coating films have shown a larger value of load at scratch and a smaller shrinkage during heat-treatment by replacing P₂O₅ in the films with B₂O₃. It has been found that B₂O₃ more effectively reduces the glass transition temperature of SiO₂ glass than P₂O₅. The concentrations of sodium ions, which migrated from soda-lime-silica glass substrates during the film formation, were higher in phosphosilicate and borophosphosilicate films than in borosilicate and pure silica films. This finding should be ascribed to the gettering effects of phosphorus for sodium ions.     

The effect of additives on the crystallization and sintering of 2MgO-2Al2O3-5SiO2 glass-ceramics

Crystallization and sintering behaviour of three cordierite (2MgO-2Al₂O₃-5SiO₂) glasses containing different amount of additives were investigated and compared by using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and the Archimedes method. The stoichiometric 2MgO-2Al₂O₃-5SiO₂ (MAS) glass and the 2MgO-2Al₂O₃-5SiO₂ glass containing 3 wt% of B₂O₃ and 3 wt% of P₂O₅ (MASBP) showed two exotherms (one for -cordierite formation from a glass and the other for -cordierite formation from the -cordierite phase), whereas the 2MgO-2Al₂O₃-5SiO₂ glass containing 2 wt % of B₂O₃, 2 wt% of P₂O₅, and 2 wt % of TiO₂ (MASBPT) showed only a single exotherm representing -cordierite formation. By using Kissinger, Augis-Bennett, Ozawa, and modified Kissinger methods, the activation energy values for -cordierite formation in the MASBP and MASBPT glasses were determined as 310±6 and 326±13 kJ mol^–1, respectively, whereas that in the MAS glass was determined as 868±5 kJ mol^–1. The MASBPT glass showed the lowest peak temperature value for -cordierite formation (980 °C) amongst the three glasses. Both the MASBP and MASBPT glasses showed excellent sintering behaviour (> 99.7% of theoretical density).     

Microstructural and dielectric behaviour of glass ceramics in the system PbO-BaO-TiO2-B2O3-SiO2

Glasses in the system PbO-BaO-TiO₂-B₂O₃-SiO₂ with and without P₂O₅ as nucleant have been prepared. The glass samples were ceramized based ondta studies. The ferroelectric phase crystallizing out has been found to be BaTiO₃ fromxrd. The optical and scanning electron micrographs show the presence of BaTiO₃ as major phase. In these glass ceramic samples, dielectric constant and dissipation factor are approximately constant with temperature and frequency upto the glass transition temperatureT _g and thereafter increase sharply with temperature and finally level off. The addition of P₂O₅ as nucleant and molar ratio of (PbO + BaO) to TiO₂ has marked influence on the dielectric behaviour and composition of ferroelectric phase crystallizing out.     

Mössbauer studies of the effect of nucleating agents on the crystallization of YIG in the Na2O-SiO2-Y2O3-Fe3O3 glass system

The effect of 2 mol % of P₂O₅ or TiO₂ on the crystallization of yttrium-iron-garnet (YIG) in Na₂O-SiO₂-Y₂O₃-Fe₂O₃ glass ceramics has been investigated by X-ray and Mössbauer spectroscopic studies. These studies indicate that the glass ceramics containing P₂O₅ are more favourable for the crystallization of YIG. Analysis of the results suggest that an optimum growth temperature for crystallization of the YIG phase is 800° C in the sample with P₂O₅ as the nucleating agent. The sample heat-treated at the growth temperature for 40 h is not as favourable for crystallization of the YIG phase as the sample which is given a two-stage heat-treatment.     

Mössbauer study of crystallization of glasses in the system K2O-Na2O-CaO-MgO-Al2O3-SiO2

Mössbauer spectroscopy has been used to study several glasses and glass ceramics based on the system K₂O-Na₂O-CaO-MgO-Al₂O₃-SiO₂ with additions of Fe₂O₃, Fe₃O₄ and P₂O₅. The change of co-ordination and proportion of Fe²⁺ and Fe³⁺ occurring during the transformation from glass to glass ceramic was studied. By means of the nuclear magnetic hyperfine splitting effect Fe₃O₄ was found in glass ceramics with more than 2% of P₂O₅. The amount of Fe₃O₄ formed was found to increase with P₂O₅ addition, but Fe₃O₄ was not identified in the glass with no P₂O₅ addition.     

New transparent Er-doped oxyfluoride tellurite glass ceramic with improved near infrared and up-conversion fluorescence properties

Transparent glass ceramics have been obtained by nucleation and growth of Y₂Te₆O₁₅ or Er₂Te₅O₁₃ cubic phase in a new Er³⁺-doped oxyfluoride tellurite glass. Effect of heat treatment on absorption spectra, luminescence and up-conversion properties in the oxyfluoride tellurite glass has been investigated. With heat treatment the ultraviolet absorption edge red shifted evidently for the oxyfluoride telluride glass. The near infrared emission that corresponds to Er³⁺:⁴I_13/2 → ⁴I_15/2 can be significantly enhanced after heat treatment. Under 980 nm LD pumping, red and green up-conversion intensity of Er³⁺ in the glass ceramic can be observed much stronger than that in the base glass.     

Studies on synthesis of calcium ferrite-based bio glass ceramics

The possibility of synthesizing a Ca-ferrite based biocompatible glass ceramic has been explored in the following two glass compositions: (i) 28Na₂O-8CaO-3P₂O₅-llFe₂O₃-50SiO₂, and (ii) 25Na₂O-8CaO-3P₂O₅-20Fe₂O₃-41SiO₂-3B₂O₃ (in weight ratio). The effect of simulated body fluid on the different glasses and glass ceramics was also investigated. While there is no direct evidence for apatite formation, the weight losses recorded and formation of a Si-rich layer at the surface appears to be an indication of onset of apatite formation. The rate of apatite formation is presumably retarded due to the presence of Al³⁺ (picked up from AL₂O₃ crucible). Ferromagnetic resonance experiments at 9.03 GHz demonstrate that these glass ceramics can possibly be used for microwave hyperthermia.     

Electrical, optical, and thermal properties of Sn-doped phase change material Ge2Sb2Te5

In this article, effect of Sn on the electrical, optical, and thermal properties of Ge₂Sb₂Te₅ is studied. Ge₂Sb₂Te₅, Ge_1.55Sb₂Te₅Sn_0.45, and Ge_1.1Sb₂Te₅Sn_0.9 alloys are prepared by melt quenching technique and their thin films are prepared by thermal evaporation on glass substrates. These materials are then characterized by differential scanning calorimetry, X-ray diffraction, optical method, and impedance measurements. Doping with Sn maintains the NaCl-type crystalline structure of Ge₂Sb₂Te₅. Activation energy (E _a) for crystallization is calculated by Kissinger’s method. E _a decreases slightly from 2.56 eV for Ge₂Sb₂Te₅ to 2.24 eV for Ge_1.1Sb₂Te₅Sn_0.9. The distinct change in extinction coefficient (k) of Ge₂Sb₂Te₅ and Sn-doped amorphous films is found in the visible region. A large increase in optical contrast (C) is observed in the Sn-doped phase change materials. The phase change transition is studied using impedance measurements as a function of temperature. Impedance measurements show the appearance of nucleation centers in samples heated at temperatures below crystallization temperature (T _c) and above glass transition temperature (T _g).     

Sb2Te3-Ta2O5 nano-composite films for low-power phase-change memory application

Sb₂Te₃-Ta₂O₅ nano-composite films were deposited by the cosputtering of Sb₂Te₃ and Ta₂O₅ targets using radio frequency magnetron sputtering system at room temperature. A phase-change random access memory (PCRAM) device based on the Sb₂Te₃-Ta₂O₅ films was successfully fabricated. Compared to a pure Ge₂Sb₂Te₅ based PCRAM cell, the reset voltage of the Sb₂Te₃-Ta₂O₅ based cell was obviously reduced, which was attributed to the reduced thermal conductivity and lower melting point of the Sb₂Te₃-Ta₂O₅ films. In addition, the device with the Sb₂Te₃-Ta₂O₅ layer could work with much shorter pulse widths for both SET and RESET, suggesting that the Sb₂Te₃-Ta₂O₅ based compounds are promising candidates for low-power and fast-speed PCRAM application.     

Effects of glass-forming histories on the crystallization kinetic of the 20Li2O–80TeO2 glass

In the present work, tellurite 20Li₂O–80TeO₂ glasses were prepared with identical nominal composition under different glass-forming histories to produce a stressed and stress-free samples. X-ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC) techniques were used to study the effects of the glass-forming histories on the thermal and structural properties of these glasses. The γ-TeO₂ (metastable), α-TeO₂ and α-Li₂Te₂O₅ phases were identified during the controlled devitrification in these glasses. The mestastable character of the γ-TeO₂ phase was clearly observed in the glass under stress but this effect is not so clear in the stress-free glass. The γ-TeO₂ and α-TeO₂ phases crystallizes during the initial stages of crystallization in both studied glasses while the α-Li₂Te₂O₅ phase crystallize in the final stages of the crystallization. The activation energies and Avrami exponent were calculated for both studied glasses with different particle size leading to E₃ > E₂ > E₁ for stressed glass and E₃ > E₂ ≈ E₁ for stress-free glass, where E₁, E₂ and E₃ were associated to the γ-TeO₂, α-TeO₂ and α-Li₂Te₂O₅ phases, respectively. The observed distinct in both glasses is an indicative that nucleation and growth takes place by more than one mechanism in the early stages of the crystallization.     

Dissolution behavior and bioactivity study of glass ceramic scaffolds in the system of CaO–P2O5–Na2O–ZnO prepared by sol–gel technique

Three-dimensional glass ceramic scaffolds from the system CaO–P₂O₅–Na₂O–ZnO have been prepared by coating polyurethane foams with sol–gel derived glass slurry. Main phase catena hexaphosphate (Ca₄P₆O₁₉), minor phases calcium pyrophosphate (β-Ca₂P₂O₇) and calcium metaphosphate (β-Ca(PO₃)₂) were detected in the prepared glass ceramics. In order to assess the potential use in hard tissue engineering, the dissolution and precipitation behavior of the glass ceramics was investigated in vitro after soaking in simulated body fluid (SBF) for different periods of time, and the bioactivity and biocompatibility studies were conducted using mouse MC3T3-E1. Ca₄P₆O₁₉ phase showed a good chemical durability in SBF solution over the period time of soaking. However, there were small quantities of apatite-like deposits formed on the surfaces after soaking 28 days, exhibiting a poor ability of inducing calcification in SBF. In vitro cell culture, a high degree of cell adhesion and spreading was achieved and large number of mineralized deposits composed of Ca, P and Zn were detected in these porous scaffolds. These results confirmed the biocompatibility and bioactivity of the glass ceramics and the positive effects on mouse MC3T3-E1 cell behavior although no continuous apatite layer was formed on scaffold surfaces after soaking in SBF, and also demonstrated that Zn doped this glass ceramics could strongly stimulate the formation of mineralized deposits in vitro culture of MC3T3-E1 cells.     

Comparison between crystal field effects on the fluorescence spectra of crystalline SmP5O14 and vitreous (Sm2O3)0.248(P2 O5)0.752

To investigate how the local symmetry of the Sm³⁺ ion affects the fluorescence of a samarium metaphosphate glass of composition (Sm₂O₃)_0.248(P₂O₅)_0.752, the temperature and pressure dependences of its laser induced fluorescence spectrum are compared with those of a samarium pentaphosphate crystal (SmP₅O₁₄). Findings include: (i) The crystal field splitting of the energy levels responsible for fluorescence in SmP₅O₁₄ at room temperature is consistent with the local symmetry of oxygen atoms of the phosphate cage around the Sm³⁺ ions being quite close to cubic – in accord with crystal structure. At 12 K there is a systematic disappearance of the shortest wavelength lines of each fluorescence band attributable to a decreasing population of higher crystal field levels, which are occupied at ambient temperature. (ii) The (Sm₂O₃)_0.248(P₂O₅)0.752_0.248 glass fluorescence spectrum forms five bands, which can be related to that of the crystal but with inhomogeneous line broadening; the short wavelength edges sharpen at low temperatures, also attributable to a decreasing population of higher crystal field levels at lower temperatures. (iii) The shifts (d/dp) in the wavelengths of the fluorescence peaks of the SmP₅O₁₄ crystal induced by pressure up to 50 kbar in a diamond anvil cell are small but measurable at room temperature, being about +0.03 nm kbar^–1 (+0.3 Å kbar^–1). Application of pressures up to 50 kbar to the (Sm₂O₃)_0.248(P₂O₅)_0.752 glass did not alter the positions of the bands within the error in the fluorescence wavelength measurements. Neither the SmP₅O₁₄ crystal nor the metaphosphate glass showed any indication of undergoing a phase transition up to the highest pressure reached. A low frequency Raman mode has been observed, which softens with reducing temperature, indicating softening of the associated optical mode and suggesting that, like other RP₅O₁₄ crystals, SmP₅O₁₄ undergoes a ferroelastic phase transition.     

Glass formation and immiscibility in the TeO2-B2O3-Fe2O3-MnO system

The glass formation in the quaternary TeO₂-B₂O₃-MnO-Fe₂O₃ system and in its ternary systems was investigated. A range of liquid immiscible phases, located near to the binary TeO₂-B₂O₃ and B₂O₃-MnO systems was established. Using transmission electron microscopy, a trend to metastable liquid-phase separation in the single-phase glasses, located near to the boundary of immiscibility was observed. With an increase in the Fe₂O₃ and MnO content still in the process of cooling of the melts, it was possible for a fine glassy crystalline structure to be formed in them. It was shown that by changing the upper limit of the melting temperature and the cooling rate, the glassy crystalline structure and the Fe₃O₄ content could be modified.     

Microstructure and dielectric properties of CBS glass-doped Sr0.5Ba0.5Nb2O6 ceramic system

40CaO–20B₂O₃–40SiO₂ (abbreviate as CBS) glass-doped Sr_0.5Ba_0.5Nb₂O₆ (SBN50) ceramics were fabricated by solid-state ceramic route. The effects of CBS glass addition on the firing, the phase formation, the microstructure and dielectric characterization of SBN50 ceramics were investigated. Results show that the density of the samples firstly increase and then slightly decrease with increasing CBS glass content and the highest density achieved has been 97% of the theoretical density for the sample with 2% (mass fraction) CBS glass. The sintering temperature was significantly reduced from 1,350 to 1,100 °C. X-ray diffraction analysis shows the single phase tungsten bronze type structure is preserved up to 2% CBS glass. However, the samples with more than 5% CBS glass are found to have a secondary phase CaNbO₃. The diffuse character and the dielectric constant at room temperature increase as CBS glass content increases. The dielectric constant of the samples at the Curie temperature (T _c) firstly increases and then decreases with increasing the content of CSB glass. Interestingly, the grain sizes of SBN phase are found to obviously increase with increase in CBS glass doping level.     

Ga as an additive in the As2Te3 glass

Results of measurements of the mean atomic volume (V), the glass transition temperature (T _g), the activation energy for glass transition (E _t) and the d. c. electrical conductivity () are reported and discussed for ten glass compositions of the Ga–As–Te system. The glasses studied can be represented as Ga _x (As_0.4Te_0.6)_100–x glasses, with the additive Ga ranging from 0 to 12 atomic percent (at.%) in the parent As₂Te₃glass. In the Ga _x (As_0.4Te_0.6)_100–x glasses, changes in slope are observed in the V, T _g, E _t, and other electronic properties, at the composition with a Ga content of 2 at.%. The results are compared with those obtained on introduction of Ag and Cu to the As₂Te₃and the [0.5As₂Te₃–0.5As₂Se₃] glasses. Analysis of the data suggest formation of GaAs, Ga₂Te₃and excess Te structural units (s.u.) in lieu of some of the original As₂Te₃s.u., for addition of Ga up to 2 at.% to the parent As₂Te₃glass; for higher Ga contents, formation of GaAs, GaTe and excess Te s.u. are indicated.     

Polycrystalline materials in MoO<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript>–V<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Melt quenching technique was applied to study tendency for phase formation and amorphization in the MoO₃–ZrO₂–V₂O₅ system. By X-ray diffraction were detected the main crystalline phases separated during the quenching: Zr(MoO₄)₂, V₂MoO₈, (Mo_0.3V_0.7)₂O₅, V_0.95Mo_0.97O₅ but in a wide concentration range the dominant crystalline phase was monoclinic ZrO₂. The average particle sizes of the obtained crystal phases were in the range 30–50 nm. A narrow glass formation area was situated, near MoO₃–V₂O₅ side. The glass-crystalline samples were obtained in the MoO₃- and V₂O₅-rich compositions. The phase formation was proven by IR analysis also. IR data showed that the main structural units built up the glass network are corner shared VO₅ and MoO₆ groups while in the corresponding crystal V₂MoO₈ phase MeO₆ (Me = V, Mo) octahedra are corner and edge shared (band at 580 cm⁻¹).