Rie Ihara

Green-emissive Mn-activated nanocrystallized glass with willemite-type Zn 2 GeO 4

We fabricated Mn2+-activated nanocrystallized glasses (NCG) with willemite-type Zn2GeO4 from a zincogermanate system glass added by various MnO-concentrations, and examined their photoluminescence (PL) properties. The Mn2+-activated NCGs indicated bright green-emission based on the 4T1→6A1 transition of the Mn2+, indicating exclusive Mn2+-occupation of Zn site in the Zn2GeO4 nanocrystals. In addition, green long-lasting photoluminescence (LLP) was also observed in the NCGs with low MnO-concentration. Relation between the MnO-concentration and the LLP property was also considered.

Formation of Zn defects in willemite-type Zn2GeO4 during supercooled liquid-crystal phase transition

This letter elucidates the formation mechanism of interstitial Zn defects in wide band-gap semiconductive willemite-type Zn2GeO4 via nanocrystallization in a zincogermanate glass. The results of time-development structural observations suggest that Zn2GeO4 nanocrystals precipitate in the nanometric Zn-condensed region, which occurs prior to nanocrystallization. The Zn-condensed environment probably promotes the capture of Zn ions in the interstitial sites of the Zn2GeO4 structure during the structural ordering of the supercooled liquid phase. The Zn-condensation mechanism is also discussed.

Crystallization of tungstenbronze-type Ba2NaNb5O15 in high-Nb2O5-content glass: An inelastic light scattering study

In situ observations of phonon Raman and Boson scattering were performed in high-Nb2O5-content barium–sodium aluminophosphate glass, which crystallizes tungstenbronze-type Ba2NaNb5O15 (BNN), during heating and subsequent cooling processes in order to examine the BNN crystallization dynamics and phase transitions. It is suggested that NbO6 clusters/cohesive regions are present and are subjected to stress by the surrounding aluminophosphate network prior to crystallization of the BNN phase. Furthermore, in the cooling period, a successive phase transition (4/mmm→4mm→mm2) of the BNN phase was observed in the glass-ceramics, implying the possibility of producing functional glass-ceramics with ferroelastic properties.

Crystallization and Morphology of Glassy Sanbornite

We investigated the crystallization and resulting morphology of a stoichiometric barium-silicate glass 1BaO-2SiO2 (glassy sanbornite) by using transmission electron microscope and Raman spectroscopy. A crystalline aggregate structure consisting of a Ba5Si8O21 phase (trunk) and a β-BaSi2O5 phase (branch) was observed in the heat-treated glassy sanbornite. The Ba-richer phase of Ba5Si8O21 precipitated prior to the formation of the stoichiometric β-BaSi2O5 phase, suggesting the presence of the region in which the Ba ions are enriched or cohesively distributed. A considerable structural similarity between the glassy sanbornite and the Ba5Si8O21 phase was also suggested in this study.

Low-frequency inelastic light scattering of zincogermanate glass in supercooledliquid regime

We performed in situ observation of low-frequency inelastic light scattering in a zincogermanate glass showing nanocrystallization of semiconductive Zn2GeO4 to elucidate the crystallization and phase transformation dynamics. In supercooledliquid state, an anomalous damping behavior of Boson peak was observed as the elastic softening happened. Combination of Boson and TEM studies revealed that the Boson damping is due to the liquid-liquid phase separation, which occurs prior to nanocrystallization, suggesting possibility of in situ spectroscopic observation of phase separation.

NANOCRYSTALLIZATION AND OPTICAL PROPERTY OF WILLEMITE-TYPE SEMICONDUCTIVE Zn2GeO4 IN GLASS

A wide band-gap semiconductive oxide Zn2GeO4 has recently attracted considerable interest because it is a multifunctional material; excellent photoluminescent (PL) and photocatalytic property, high-capacity anode for lithium batteries, and so on. Recently, present authors group have fabricated transparent Zn2GeO4-nanocrystallized glass from a lithium zincogermanate glass. This article briefly describes a series of our studies on the nanocrystallized glass. Particularly, the phase-formation dynamics in supercooled-liquid phase and PL property of nanocrystallized glasses are presented.

Chemical Compositions and Crystallization Behavior of BaO-TiO2-GeO2 Glass

We prepared glasses in 30BaO-(15+x)TiO2-(55–x)GeO2 composition (x=0, 10, 20, 35) and examined their crystallization behavior. Relation of crystallizing-phase to optical transparency in the resulting crystallized sample was also considered. Although the glass samples with x=0-20, which precipitate fresnoite-type Ba2TiGe2O8 as main phase, lost transparency after crystallization, the glass with x=30, which precipitates BaTi4O9 phase, kept good transparency. Dependence of transparency on the x is also discussed.

In situ Observation of Supercooled Liquid--Crystal Phase Transition in Glassy Ferroelectric LaBGeO5

Inelastic light scattering was observed in situ from glassy ferroelectric LaBGeO5, which crystallizes the stillwellite-type stoichiometric phase, in the glass–supercooled liquid (SCL) and subsequent SCL–crystal phase transition regimes. The dynamics of the planar BO3 unit in the crystal growth period of the crystallization process was clarified through in situ observation.

Fabrication and Photoluminescent Property of Transparent Nanocrystallized-Glass in Li2O-ZnO-GeO2 System

We investigated crystallization behaviour of several glasses in ternary Li2O-ZnO-GeO2 system in order to fabricate the glass-ceramics consisting of Zn-related compound showing photoluminescent property. Nanocrystallized glass with willemite-type Zn2GeO4 could be prepared from the 15Li2O-15ZnO-70GeO2 glass, and revealed a long-lasting photoluminescence (LLP). Origin of the LLP in the nanocrystallized glass is also discussed.

Crystallization of Tungstenbronze Phase and its Inelastic Light Scattering in Niobiophosphate-System Glass

We prepared a niobiophosphate-glass-crystallizing tungstenbronze-type Ba2NaNb5O15 and measured elastic light scattering spectra in situ in the glass-ceramics fabrication regime. We found that the studied glass possesses a strong tendency for phase separation into Al2O3P2O5 and Nb-rich regions prior to crystallization. It is suggested that the tungstenbronze phase crystallizes in the Nb-rich region separated from the supercooled liquid phase. This study demonstrated that in situ Raman spectroscopy is also useful for observing the phase separation dynamics in glass.