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Title: Local structure of alkalis in mixed alkali borate glass to elucidate the origin of mixed-alkali effect
Authors: Tokuda, Yomei
Kaneko, Shun-ichi
Takahashi, Yuya
Masai, Hirokazu
Ueda, Yoshikatsu
Hara, Kenji
Fujimura, Shigeto
Ono, Yuji
Yoko, Toshinobu
Author's alias: 徳田, 陽明
正井, 博和
上田, 義勝
横尾, 俊信
Keywords: NMR
Borate glass
Mixed-alkali effect
Issue Date: Dec-2015
Publisher: Elsevier B.V.
Journal title: Journal of Asian Ceramic Societies
Volume: 3
Issue: 4
Start page: 412
End page: 416
Abstract: We report the structural analysis of Na⁺ and Cs⁺ in sodium cesium borate crystals and glasses using ²³Na and ¹³³Cs magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The composition dependence of NMR spectra of the borate was similar to that of the silicate: (1) the peak position of cesium borate crystals shifted to upfield for structures with larger Cs⁺ coordination numbers, (2) the MAS NMR spectra of xNa₂O-yCs₂O-3B₂O₃ (x = 0, 0.25, 0.5, 0.75, 1.0, x + y = 1) glass showed that the average coordination number (CN) of both the alkali cations decreases with increasing Cs⁺/(Na⁺ + Cs⁺) ratio. However, the degree of decrement in borates is much smaller than that in silicates. We have considered that the small difference in CN is due to 4-coordinated B, because it is electrically compensated by the alkali metal ions resulting in the restriction of having various coordinations of O to alkali metal.
Rights: © 2015 The Ceramic Society of Japan and the Korean Ceramic Society. Production and hosting by Elsevier B.V. Under a Creative Commons license.
DOI(Published Version): 10.1016/j.jascer.2015.09.002
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