Prominent Nanocrystallization of 25K2O·25Nb2O5·50GeO2 Glass |
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Authors: | Kazuhiro Narita Yoshihiro Takahashi Yasuhiko Benino Takumi Fujiwara Takayuki Komatsu Takeshi Hanada Yoshihiko Hirotsu |
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Affiliation: | Department of Chemistry, Nagaoka University of Technology, 1603–1 Kamitomioka-cho, Nagaoka 940–2188, Japan;Institute of Scientific and Industrial Research, Osaka University, 8–1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan |
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Abstract: | Some K2O-Nb2O5-GeO2 glasses are prepared, and their crystallization behaviors are examined. 25K2O·25Nb2O5·50GeO2 glass with the glass transition temperature T g= 622°3C and crystallization onset temperature T x= 668°3C shows a prominent nanocrystallization. The crystalline phase is K3,8Nb5Ge3O20,4 with an orthorhombic structure. The sizes of crystals in the crystallized glasses heat-treated at 630° and 720°3C for 1 h are °10 and 20–30 nm, respectively, and the crystallized glasses obtained by heat treatments at 620°-850°3C for 1 h maintain good transparency. The density of crystallized glasses increases gradually with increasing heat-treatment temperature, and the volume fraction of crystals in the sample heat-treated at 630°3C for 1 h is estimated to be ~35%. The usual Vickers hardness and Martens hardness (estimated by nanoindentation) of 25K2O·25Nb2O5·50GeO2 glass change steeply by heat treatment at T g, i.e., at around 35% volume fraction of nanocrystals. The present study demonstrates that the composite of nanocrystals and the glassy phase has a strong resistance against deformation during Vickers indenter loading in crystallized glasses. |
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