Effect of alkali and alkaline-earth cations on the neodymium environment in a rare-earth rich aluminoborosilicate glass

Abstract

The local structure around neodymium in an aluminoborosilicate glass bearing 3.6 mol% Nd 2 O 3 is studied by optical absorption spectroscopy and EXAFS at the Nd L III -and K-edges. The influence of the nature of alkalis (M + = Li + , Na + , K + , Rb + , Cs + ) and alkalineearths (M 2+ = Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ ) on the coordination sphere of Nd 3+ ions in the glass is particularly investigated. The Nd 3+ sites are well-defined with NdAO mean distances of 2.46 ± 0.03 Å , whatever the alkali and alkaline-earth ion type except Li + and Mg 2+ , for which glasses exhibit slightly more disordered Nd sites and longer NdAO distances (2.49 ± 0.03 Å ). Using bond valence considerations, a model is proposed for the Nd site, and consists in 7-8 non-bridging oxygens (NBO), every NBO being charge compensated by 2-3 alkalis and alkaline-earths. The NdAO mean distance is adjusted according to the mean field strength of these cations, to avoid overbonding of the NBO's. A glass series with varying Ca 2+ /Na + concentration ratio shows that Nd 3+ cations are able to maintain this average coordination site even at high alkaline-earth content.

Spectroscopic and structural properties of Cr3+ in silicate glasses: Cr3+ does not probe the average glass structure

“…It is noticeable that a similar preference of cations for Na versus Ca next-nearest neighbors has been shown for Nd 3+ in aluminoborosilicate glasses [59] and for Mo VI in borosilicate glasses [60].…”

“…Charge compensation considerations bring some light on this location preference, as was shown by the bond valence model for Nd 3+ [59]. According to this model, the sum of the bond valences The low value of the bond valence brought by large alkalis with large polarisability (K, Na) allows to adjust accurately the charge of the O ligands of Cr 3+ , as depicted in Fig.…”

Effect of neodymium oxide on the solubility of MoO3 in an aluminoborosilicate glass

“…Nd 3+ ions remain located in the depolymerized silicate regions of the glassy network and thanks to their high field strength [51], they impose their local environment composed of 6 to 8 NBOs [56,57]. Nevertheless, in order to insure locally the configuration electroneutrality, a fraction of the lower field strength modifier cations present in the glass composition such as alkali and alkaline-earth cations are located in the second coordination sphere of the Nd 3+ cations [51,56,57].…”

Effect of boron oxide addition on the Nd3+ environment in a Nd-rich soda-lime aluminoborosilicate glass

“…This suggests an effect of La 2 O 3 on the Si/B mixing of the network and a competition between La and alkali cations for the bonding to the borate component, that may be consistent with the RE-metaborate model although the authors did not explicitly refer to it. In our own work on Nd 2 O 3 -bearing sodium and calcium aluminorobosilicate glasses, we noticed that the Nd local environment, as examined using optical absorption and EXAFS spectroscopy at the Nd L 3 and K-edges, more closely resembles that of an alkali silicate matrix rather than that of a Nd-metaborate or alkali borate matrix [16,17]. In the framework of research for containment glasses with increased nuclear waste load, we performed a systematic study of the effect of boron oxide on the structure and crystallization tendency of these glasses.…”

“…On the other hand, B 2 O 3 may partly react with RE oxide to form BO 4 units, directly inducing either dispersion or concentration of RE cations within the glass, according to the B 2 O 3 content. Incorporation of large amounts of RE in aluminoborosilicate glasses has been studied in the framework of nuclear waste containment research [7][8][9][10][11][12][13][14][15][16]. The Gd 2 O 3 solubility limit has been systematically determined in numerous peralkaline [7] and peraluminous [8] sodium aluminoborosilicate glass compositions.…”