Ryuji Sato

Optical properties of transparent glass-ceramics in K2ONb2O5TeO2 glasses

Abstract Transparent glass-ceramics consisting of a cubic crystalline phase with crystallites having diameters between 20 and 40 nm in the composition of 15K 2 O15Nb 2 O 5 70TeO 2 (mol%) have been fabricated. A phase with cubic structure is formed by post-heat-treatment at around 390°C for 1 h and transforms into a stable phase at temperatures above 450°C. The glass-ceramics consisting of a stable crystalline phase are opaque. The transparency of glass-ceramics is attributed to a small particle size (average radius: 10–20 nm) of the cubic crystalline phase. The optical and dielectric properties for the transparent glass-ceramics obtained by heat-treatment at 425°C for 1 h are: refractive index, n = 2.11 ± 0.02; relative permittivity (1 kHz, 300 K), ϵ r = 44 ± 1 and third-order non-linear optical susceptibility, χ (3) = 3.3 × 10 −13 esu. These values are larger than those for the original base glass, i.e. n = 2.02 ± 0.02, ϵ r = 28 ± 1 and χ (3) = 0.9 × 10 −13 esu. Second-harmonic generation is clearly observed in transparent glass-ceramics. These transparent glass-ceramics have a potential as a new type of non-linear optical material.

Crystallization of LiNbO3 in tellurite glasses

Abstract TeO 2 Li 2 ONb 2 O 5 glasses were prepared using conventional melt quenching and the precipitation behavior of LiNbO 3 crystals was examined. LiNbO 3 crystals precipitated directly from 50TeO 2 −(50− x )Li 2 O− x Nb 2 O 5 glasses with high Li + contents without passing through the metastable pyrochlore-type compound. Transparent oxide glasses containing 10 μm diameter LiNbO 3 crystals were prepared using a two-step heat-treatment process.

Superconducting glass ceramics with Tc=100 K based on the Bi‐Pb‐Sr‐Ca‐Cu‐O system

Superconducting glass ceramics of Bi0.8Pb0.2SrCaCu1.5Oy (sample A) and BiPb0.2SrCaCu1.5Oy (sample B) have been prepared by using the melt quenching method. It was found that the volume fraction of the high Tc phases in sample A annealed at 830 or 840 °C for 250 h was much higher than that in sample B. The annealed (840 °C, 250 h) sample A exhibited superconductivity with a Tc (zero) of 100 K and a critical current density (77 K, zero magnetic field) of 120 A/cm2.

Effect of Cu+/Cu2+ ratio on the thermal stability and crystallization in Bi2Sr2CaCu2Ox glass

Abstract The Cu+/Cu2+ ratio in B2Sr2CaCu2Oχ glass was controlled by adding glucose (0−2.5 wt%) during glass melting, and the thermal stability and crystallization behavior of glasses with different Cu+/Cu2+ ratios was examined. In a glass melted with 2.0 wt% glucose, more than 90% of Cu ions were present as Cu+ ions. It was found that thermal stability increased with increasing Cu+. At ∼ 780°C, a liquid phase was created in the presence of Cu+ ions in the interior of samples. After oxidation of Cu+ ions to Cu2+ ions due to the oxygen diffusion through a liquid phase, the superconducting B2Sr2CaCu2Oχ phase was formed.

Incorporation of LiNbO3 crystals into tellurite glasses

Transparent tellurite glasses containing 5–10 μm diameter LiNbO3 crystals (3–7 wt%) have been successfully prepared using an incorporation method in which LiNbO3 crystals are directly dispersed into the 80TeO2-15Li2O-5Nb2O5 glass. The dissolution behaviour of the LiNbO3 crystals greatly depends on the Li2O: Nb2O5 ratio in the matrix glasses. In the 80TeO2-10Li2O-10Nb2O5 matrix glass, the crystals remaining after incorporation have the composition LiNb3O8. A small difference in the refractive indices, n, between the TeO2-based glasses (n=2.07) and the incorporated LiNbO3 crystals (n=2.296) is a significant reason for the transparency. It is feasible to prepare the highly transparent TeO2-based glasses containing a large amount of LiNbO3 crystals by controlling the incorporation process.

Preparation of Ag‐coated superconducting Bi2Sr2CaCu2Ox glass‐ceramic fibers

The Ag‐coated superconducting Bi2 Sr2 CaCu2 Ox glass‐ceramic fibers were successfully prepared. The glass fibers with a length of 50 cm, a width of 100–200 μm, and a thickness of about 20 μm were first drawn from glass plates with a thickness of 1 mm and then silver pastes were coated on the smooth surface of glass fibers. The Ag‐coated glass fibers were converted into superconductors after annealing at temperatures of 820–860 °C. The main crystalline phase in the glass‐ceramic fibers was the superconducting low Tc phase. The Ag‐coated glass‐ceramic fibers obtained by annealing at 840 °C for 5 h in air exhibited superconductivity with a Tc (zero)=70 K and a critical current density (60 K, zero magnetic field) of more than 40 A/cm2 .

Effect of copper content on glass formation and superconductivity in the Bi-Pb-Sr-Ca-Cu-O system

High-Tc superconducting ceramics of formula Bi0.8Pb0.2SrCaCuxOy (x=1.5, 1.8 and 2.0) were prepared by using the melt-quenching method, and the effect of copper content on glass formation and superconductivity was examined. It was found that the composition withx=1.5 had a tendency to form a glass and Bi2(Sr, Ca)2CuOy crystals tended to precipitate easily during the rapid quenching of melts in the compositions withx=1.8 and 2.0. It was found from the temperature dependence of a.c. complex susceptibility that the intergrain coupling of superconducting crystals in the samples obtained was weak, but the weak coupling was improved by increasing the annealing time. The superconducting glass-ceramics Bi0.8Pb0.2SrCaCu1.5Oy exhibited superconductivity with aTc (zero) of 106 K and aJc of 250 Acm−2.

Thermal stability and hopping conduction in Bi4Sr3Ca3CuxOy glasses (x = 4–9)

Abstract The thermal stability and transport properties of Bi 4 Sr 3 Ca 3 Cu x O y glasses with different Cu contents, 4 ≤ x ≤ 9, and Cu valence states, R(Cu + ) = Cu + /(Cu + + Cu 2+ ) with 0.7 ≤ R ≤ 1, have been examined. The Cu content dependence of thermal stability, electrical conductivity and activation energy for conduction is not monotonic, but the magnitudes of these properties change at the composition x ≅ 6.5. The effect of R (Cu + ) on the conduction of BiSrCaCuO glasses has been measured and the conductivity is analyzed using the Mott equation for electron conduction of glasses containing transition metal ions; the results suggest that the polaron hopping mechanism between Cu + and Cu 2+ is appropriate for the conduction of all Bi 4 Sr 3 Ca 3 Cu x O y glasses irrespective of Cu content. A new structure model, particularly on the role of Cu + , has been proposed for the present glasses, in which Cu + ions act as both network formers and modifiers depending on the ratio of Cu + Bi 3+ .

119Sn-mössbauer, IR, and DSC study of tin oxyfluoride glasses

The119Sn-Mössbauer spectra ofxSnO·(70−x)SnF2·30P2O5 glasses (0 ≤x≤70) measured at 78 K comprised a doublet due to Sn2+ (δ=3.30–3.36 mm s−1, Δ = 1.70–1.72 mm s−1) and a weak singlet due to Sn4+ located at −0.23 mm s−1 with respect to BaSnO3. The δ and Δ of Sn2+ were comparable to those of Sn2P2O7. Small Debye temperatures (146 and 155 K) were obtained from the low-temperature measurements. These results indicate that Sn2+ and Sn4+ occupied interstitial sites, being loosely and ionically bonded to distorted PO4−xFx tetrahedra.

Low-temperature deformation of fluoride and oxide glass fibers below their glass transition temperatures

Abstract Deformation of some fluoride and oxide glass fibers were measured at temperatures below their glass transition temperatures. Glass fibers were wound on a cylinder, kept at low temperatures for various times and the remaining strains of fibers after the heat treatment were measured. It was found that the temperature region in which fluoride glass fibers are deformed is much lower than that for oxide glass fibers. The deformation mechanisms of each of the glass fibers were analyzed based on a log-normal distribution model of relaxation times. It was found that the activation energy for low-temperature deformation is much lower than that for viscous flow near the glass transition temperature. It was concluded that the deformations of each of the glass fibers are caused by different relaxation mechanisms.