Papers by Author: Takumi Fujiwara

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: In-situ observation of inelastic light scattering of boson region in glassy Ba2TiGe2O8 (BTG) was performed during heating process. The in-situ boson observation revealed structural relaxation below glass-transition temperature in the as-quenched sample, suggesting the nanometric structural heterogeneity. Relation of the boson behavior to crystallization tendency is also discussed.

Abstract: We examined photoluminescent (PL) and afterglow properties in bazirite (BaZrSi3O9) phases with Sr2+-, Sn4+-, Ge4+-, and Ti4+-impurities, in order to elucidate effect of the impurity-addition on these properties. The bazirite phases studied showed blue PL and afterglow regardless of sort of the impurities. Origin of PL and afterglow emission in the bazirite phase is also discussed.

Abstract: Correlation between surface crystallization behavior of BaO-TiO2-GeO2 (BTG) glass and the thermal stability parameter measured by Differential Thermal Analysis (DTA) was examined. We have proposed normalized thermal stability ΔTnorm of the BTG glass using crystallization temperature (Tx), glass transition temperature (Tg), and melting temperature (Tm). It was found that surface crystallization occurred in the BTG glass possessing ΔTnorm (= (Tx-Tg)/Tm) value larger than 0.08. Compared ΔTnorm value of bulk state with that of powdered state, it has been revealed that Ba2TiGe2O8 was precipitated independently of thermal stabilities whereas BaTiGe3O9 or BaGe4O9 was precipitated in precursor glasses possessing high surface stability.

Abstract: We investigated the crystallization behavior of langasite-type phases in the stoichiometric corresponding glasses, i.e., Na2CaGe6O14, Na2SrGe6O14 and Pb3Ga2Ge4O14. The langasite-type phases singly were formed by heat-treatment in the glasses. Raman spectroscopy revealed the structural similarity on the scale of short-/medium-range order between the langasite-type phases and the corresponding glasses. Furthermore, we also examined the temperature dependence of second-harmonic (SH) intensity of the langasite-type phases. The SH-temperature curves exhibited an anomalous behavior, implying a structural change, e.g., isomorphous phase transition.

Abstract: Crystallization behavior of the fresnoite-type Ba2TiGe2O8 (BTG) with a large optical nonlinearity has been examined in the BaO-TiO2-GeO2 glass thin film fabricated by a RF sputtering technique and the corresponding glass (same composition of thin film, i.e., 28BaO-22TiO2-50GeO2). Both the glass thin film and the corresponding glass were crystallized by the heat-treatment, keeping a good transparency. Initial formation of BTG phase followed by the BaGe4O9 phase was confirmed in the both glass samples. In addition, the BTG crystallites in the both glass samples indicated the preferential (211) orientation. Crystallization behavior confirmed in this study was quite different from the previous study about the 30BaO-15TiO2-55GeO2 glass.