Structural study of a rare earth-rich aluminoborosilicate glass containing various alkali and alkaline-earth modifier cations
A rare-earth rich aluminoborosilicate glass of composition (given in wt.%): 50.68 SiO2 - 4.25 Al2O3 - 8.50 B2O3 - 12.19 M2O - 4.84 M'O - 3.19 ZrO2 - 16.35 Nd2O3 (where M and M' are respectively an alkali and alkaline earth cation) is currently under study as potential nuclear waste form. In this work, we were interested in the structure of this glass in relation with the modifier cation type. Two different glass series were elaborated by changing separately the nature of the alkaline (M=Li, Na, K, Rb, Cs) and the alkaline-earth (M'=Mg, Ca, Sr, Ba) ions and different structural studies were intended to elucidate the local environment of the rare-earth and the network arrangement. Only slight effect was put in evidence on the covalency degree and the length of Nd-O linkage with a change of M or M', by optical spectroscopy and EXAFS measurements. Raman and MAS NMR (29Si, 27Al, 11B) spectroscopies showed a variation of the polymerization degree of the network with the size of the modifier cation. Finally, the most important feature of this glass composition is related to the AlO4- charge compensation which was proved to be uniquely assured by alkali cations.