Abstract
We conducted structural analysis of xNa2O-yY2O3-5B2O3-3Al2O3 and xNa2O-yLa2O3-5B2O3-3Al2O3 glasses to elucidate the additive effects of rare-earth ions in these sodium aluminoborate glasses, and investigated the local environment surrounding Na+ in them by using 23Na and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The amount of higher-coordinated Al species ([5]Al and [6]Al) gradually increased in response to an increase in the ratios of Y2O3 to Al2O3 and La2O3 to Al2O3 in each type of glass, respectively. Moreover, the difference in the cation field strength (CFS) between Y3+ and La3+ was observed to affect the generation of [5]Al and [6]Al, especially when the amount of these ions in the glasses increased. In addition to the above, the coordination number of Na+ ions increased with an increase in the number of rare earth ions, confirmed by comparing results with NMR spectra of crystalline Na2Al2B2O7. The latter possibly occurred due to the oxygen concentration on Al[5] and Al[6]. Finally, it was confirmed that the formation of [5]Al and [6]Al decreases molar volume in oxide glasses, which might be partially due to better atomic packing of [5]Al and [6]Al.
Highlights
We conducted structural analysis of xNa2O-yY2O3-5B2O3-3Al2O3 and xNa2OyLa2O3-5B2O3-3Al2O3 glasses to elucidate the additive effects of rare-earth ions in these sodium aluminoborate glasses, and investigated the local environment surrounding Na+ in them by using 23Na and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy
Three kinds of Al coordination exist: 4-coordinated [4]Al, 5-coordinated [5]Al, and 6-coordinated [6]Al, which can all be quantitatively measured by magic angle spinning nuclear magnetic resonance (MAS NMR) [3] [4]
The 27Al MAS NMR spectra of yttrium sodium aluminoborate glasses and lanthanum sodium aluminoborate glasses are shown in Figure 1 and Figure 2, respectively
Summary
Considering the development of functional glasses, it is important to investigate the relation between more complex compositions, Al coordination, and physical properties, because commercially used glass for optical or building applications contains several elements. It would be interesting if, even in glasses that contain four or five elements, rare-earth ions can produce higher coordinated Al species that affect the physical properties of the glass
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