Takumi Fujiwara

Correlation between emission property and concentration of Sn^2+ center in the SnO-ZnO-P_2O_5 glass

The authors report on the correlation between the photoluminescence (PL) property and the SnO amount in SnO-ZnO-P2O5 (SZP) glass. In the PL excitation (PLE) spectra of the SZP glass containing Sn2+ emission center, two S1 states, one of which is strongly affected by SnO amount, are assumed to exist. The PLE band closely correlates with the optical band edge originating from Sn2+ species, and they both largely red-shifts with increasing amount of SnO. The emission decay time of the SZP glass decreased with increasing amount of SnO and the internal quantum efficiencies of the SZP glasses containing 1~5 mol% of SnO are comparable to that of MgWO4. It is expected that the composition-dependent S1 state (the lower energy excitation band) governs the quantum efficiency of the SZP glasses.

Microstructure of Transparent Strontium Fresnoite Glass-Ceramics

Glass-ceramics grown from a glass of the composition Sr2TiSi2.45O8.9 (STS 45) are analyzed by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Oriented nucleation with the c-axes preferably perpendicular to the surface is detected. A very strong 001-texture is observed after only 10u2005μm of growth into the bulk, making this the first system in which an orientation preferred during nucleation prevails during growth into the bulk in glass-ceramics. Piezoelectric measurements are performed and d33-values presented and discussed. The obtained results are critically viewed with respect to the two growth models describing Sr2TiSi2O8 growth in glasses.

Ultra-low propagation losses in fresnoite-type precipitated crystallized glasses

The propagation losses for fresnoite-phase crystallized glasses fabricated from 35BaO–15TiO2–50GeO2, 28BaO–18TiO2–54SiO2, and 35SrO–20TiO2–45SiO2 (STS45) glasses using a cut-back technique are reported. The values are comparable with those for LiNbO3 waveguide single crystals and transparent Y3Al5O12 ceramics. In addition, the propagation loss data indicate that the losses depend on the relationship between the polarization direction and crystal growth direction. The lowest propagation loss value (0.6 dB/cm) was measured for the STS45 crystallized glass; this value is the lowest value ever reported for an oriented crystallized glass.

Multiferroic BiFeO3 glass-ceramics: Phase formation and physical property

A production of polycrystalline phase with glassy precursor, i.e., glass-ceramics processing, has a great potential to fabricate the sophisticated materials. In this study, we have prepared the Bi2O3–Fe2O3–BaO–B2O3 system precursor, in which BiFeO3 phase is crystallizable, and examined the phase formation and physical properties in resulting glass-ceramics. We found both ferroelectricity and ferromagnetism in the glass-ceramics consisting of BiFeO3 phase, i.e., multiferroic glass-ceramics. This study has demonstrated an alternative method for synthesis of polycrystalline BiFeO3 material.

Affects of supercooled liquid state on the properties of the crystallized phase: Microscopic and spectroscopic observations in ZnO-crystallized glass-ceramics

We examined the crystallization and crystal growth of ZnO in the viscoelastic supercooled liquid (SCL) phase based on microscopic and spectroscopic observations. The resulting glass–ceramics exhibits complex ZnO dendrites that precede the formation of Zn-rich regions because of phase separation. Compressive stresses are concentrated at the interface of ZnO crystals and SCL phase, suggesting that the domains are subject to a resistance during ZnO crystal growth. Defects were detected in the crystallized ZnO and attributed to the suppression of smooth ordering of the Zn-rich regions in the SCL phase.

Large enhancement of photocatalytic activity by chemical etching of TiO2 crystallized glass

The authors aim to report the largest enhancement of photocatalytic activity by chemical etching in anatase-type TiO2 crystallized glass. Optimization of several conditions for crystallization behavior and chemical etching to realize the nano-structured ceramics (NSC) has been performed in the crystallized glass. NSC-fabrication by chemical etching in the crystallized glass is one of the most effective solutions to provide bulk materials with high specific surface area. We have found that the best condition for the NSC fabrication as a novel bulk photocatalyst in our glass system, and have obtained 16 times higher catalytic activity than that of non-etched one.

Pockels effect of silicate glass-ceramics: Observation of optical modulation in Mach–Zehnder system

Silicate glass has been used for long time because of its advantages from material’s viewpoint. In this paper, we report the observation of Pockels effect by Mach–Zehnder interferometer in polycrystalline ceramics made from a ternary silicate glass via crystallization due to heat-treatment, i.e., glass-ceramics. Since the silicate system is employed as the precursor, merits of glass material are fully utilized to fabricate the optical device component, in addition to that of functional crystalline material, leading us to provide an electro-optic device, which is introducible into glass-fiber network.

High thermal stability of red emission in Mn-doped benitoite-type strontium silicogermanate

We assessed the photoluminescence performance characteristics of Mn4+-doped tetragermanate and silicogermanate phases with a benitoite-type structure. We observed a visible red emission based on the 2E → 4A2 transition in the doped benitoite-type tetragermanate. The partial substitution of Si for Ge, resulting in SrGe3.495Mn0.005Si0.5O9, improved the internal quantum efficiency and thermal stability of the red emission. A possible explanation of the substitution effect was reasonably presented on the basis of the connectivity of luminescent polyhedral units and the decrease in the Franck–Condon off-set value in the benitoite structure.

Crystal domain growth driven by nanometric phase separation in perfect surface crystallization

Phase separation often makes glass structure inhomogeneous. Nevertheless, a uniform texture consisting of single-crystal domains has been found by crystallization in nonstoichiometric glass, i.e., perfect surface-crystallization (PSC). Although the PSC is probably caused by evolution of SiO2-rich amorphous nanoparasites on the domain, its mechanism has not been understood yet. In this study, we examined an early-stage of PSC in a strontium-titanosilicate glass by means of nanoscopic observations. It was demonstrated that the binodal-like nanometric phase-separation and crystal-growth of fresnoite-type phase occur simultaneously at the crystal interface. It was strongly suggested that the PSC process is driven by the phase separation.

Low-temperature excess heat capacity in fresnoite glass and crystal

The effect of thermal annealing on low-temperature excess heat capacity was investigated in fresnoite (Ba2TiSi2O8) glass. The amplitudes of the excess heat capacity decreased, and their positions shifted to a higher temperature by relaxation or crystallization. In particular, we revealed that the change in the excess heat capacity during transition from the glassy state to the crystalline state is relatively small compared with that of other oxides. Therefore, it is suggested that distribution of the excess vibrational density of states of the glass is similar to that of the corresponding crystal.