Transparent glass-ceramics consisting of a cubic crystalline phase with crystallites having diameters between 20 and 40 nm in the composition of 15K2O15Nb2O570TeO2 (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), ϵr = 44 ± 1 and third-order non-linear optical susceptibility, χ(3) = 3.3 × 10−13esu. These values are larger than those for the original base glass, i.e. n = 2.02 ± 0.02, ϵr = 28 ± 1 and χ(3) = 0.9 × 10−13esu. 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.

Optical properties of transparent glass-ceramics in K2ONb2O5TeO2 glasses

Classification of oxide glasses: A polarizability approach

Bismuth modified physical, structural and optical properties of mid-IR transparent zinc boro-tellurite glasses

The thermal stability and heat capacity changes in the glass transition region of K 2 O–WO 3 –TeO 2 glasses (glass formation range 20–90 mol% TeO 2 ) have been studied to examine the structural relaxation behavior. The glasses with 60–70 mol% TeO 2 and with both K 2 O and WO 3 are thermally stable against crystallization. It is proposed from Raman spectral analyses that TeO 4 trigonal bipyramids change to TeO 3 trigonal pyramids with the addition of K 2 O and that Te–O–W bonds are formed in the substitution of WO 3 for TeO 2 . Heat capacity changes of ΔC p =48–58 J mol −1 K −1 ( ΔC p = C p l − C p g , C p g and C p l are the heat capacities of the glasses and supercooled liquids, respectively), and ratios C p l / C p g = 1.6–1.8 are obtained for x K 2 O · x WO 3 · (100 − 2 x )TeO 2 glasses. The ΔC p and C p l / C p g increase with decreasing TeO 2 content, indicating an increase in thermodynamic fragility with decreasing TeO 2 content. But, the kinetic fragility estimated from the activation energy for viscous flow is almost constant irrespective of TeO 2 content. These behaviors have been analyzed using the configurational entropy model proposed by Adam and Gibbs. The results indicate that in K 2 O–WO 3 –TeO 2 glasses, Te–O–Te bonds are weak and bond breakings occur easily in the glass transition region, leading to large configurational entropy changes and thus large ΔC p .

Thermal stability and heat capacity changes at the glass transition in K2O–WO3–TeO2 glasses

Tellurite glasses. Part 1. Elastic properties

(100−x)TeO2−xLiNbO3 (x = 10−60) glasses were prepared by using a conventional melt-quenching method, and some properties such as thermal stability, density and refractive index and crystallization behaviors of glasses were measured. The thermal stability of the glasses with x = 20 and 30 was high. The density of glasses decreased monotonically with increasing LiNbO3 content from 5.50 g/cm3 to 4.58 g/cm3. The values of the refractive index of glasses were 2.04-2.11 and showed an anomalous compositional dependence. It was found from Raman scattering spectra that the structure of glasses was composed of the structural units of TeO4 trigonal bipyramid, TeO3 trigonal pyramid and NbO6 octahedra. In the glasses with x = 10 and 20, α-TeO2 (paratellurite) crystals were precipitated by heat treatment above 450°C. In the glasses with x ≧ 40, LiNbO3 crystals were formed through the transformation of a metastable pyrochlore-type compound at temperatures above 500°C. From the present study, it is proposed that the fabrication of transparent TeO2-based glasses containing ferroelectric LiNbO3 microcrystallites may be possible.

Properties and crystallization behaviors of TeO2LiNbO3 glasses

Raman scattering study on local structures of Te4+ and Nb5+ in LiNbO3-TeO2 glasses

Raman scattering spectra of CdS microcrystallites in silicate glasses

The non-linear optical properties of microcrystalline semiconductor-doped glasses have received much attention in recent years [1]. In semiconductordoped glasses, the requirement for detailed information on particle size, size distributions and chemical compositions of microcrystalline semiconductors such as CdS or CdSl_xSex is inevitable to clarify the quantum confinement effect in semiconductors. Borrelli et al. [2] proposed from X-ray diffraction analyses that in some Corning sharp cut filter borositicate glasses containing ZnO, a solid solution Cd0.65Zn0.35S was formed during annealing. Very recently, Komatsu et al. [3] examined the Raman scattering spectra of CdS microcrystallites in Zn-free and Zn-added sodium silicate glasses and found that Cdl_,ZnxS solid solutions such as Cd08Zn0.2S were formed in the Zn-added glasses. Since the amount of soluble CdS in silicate glasses depends strongly on the amount of ZnO present in glasses [3], the role of zinc in silicate glasses is of much interest and it is important to clarify the effect of zinc on the state of sulphur in glasses and also in heat-treated samples. In this study we prepared sodium silicate glasses containing sulphur or ZnS and measured the optical absorption and Raman scattering spectra of the glasses and heat-treated samples in order to clarify the state of zinc and sulphur. In particular, we focus our attention on Zn-S bonds in glasses. The state of sulphur in the so-called sulphur-amber glasses has been studied extensively, and it is well known that a rich amber colour is produced by the combination of sulphur and iron oxide in sodium silicate glasses melted under strongly reducing conditions [4-6]. However, the study of Zn-S bonds in silicate glasses has not been reported and the presence of Zn-S bonds has not been confirmed experimentally. Silicate glasses with nominal compositions 55SiO2-30Na20-15CaO (reel%) containing various amounts of sulphur (0 .5 -3wt%) or ZnS (3-6 wt %) were prepared by using a conventional melt-quenching method. A platinum crucible was used, and the melting temperature and time were 1350 °C and 90 min, respectively. In order to release the internal stress in glasses the melts were poured onto an iron plate heated at around 300 °C. The glass transition, Tg, and crystallization, Tx, temperatures of a base glass 55SiO2-30Na20-15CaO were 488 °C and 607 °C, respectively. Optical absorption spectra were measured with a Hitachi U-3210 spectrometer. Raman scattering spectra at room temperature were measured by using an Ar ÷ laser (wavelength 514.5nm and laser power

Hiroharu Mohri

Papers

Properties and crystallization behaviors of TeO2LiNbO3 glasses

Raman scattering study on local structures of Te4+ and Nb5+ in LiNbO3-TeO2 glasses

Raman scattering spectra of CdS microcrystallites in silicate glasses

Optical absorption and Raman scattering spectra of Zn-S bonds in silicate glasses