Influence of high-pressure on the short-range structure of Ca or Na aluminoborosilicate glasses from 11B and 27Al solid-state NMR
Sami Soudani, Michaël Paris, Yann Morizet
Abstract
The present study investigates the boron and aluminium speciation of aluminoborosilicate glasses synthesised under ambient to high-pressure conditions (up to 2.0 GPa) using 11 B and 27 Al Nuclear Magnetic Resonance. Four glass series were prepared in the SiO 2 -Al 2 O 3 -B 2 O 3 -Na 2 O/CaO system, with either high or low R' values (R'=([Na 2 O]+[CaO])/([B 2 O 3 ]+[Al 2 O 3 ])). 11 B NMR reveals a linear increase in four-coordinated boron (BO 4 ) with pressure for Ca glasses and non-linear with a plateau between 0.5 and 1.5 GPa for Na glasses. 27 Al NMR reveals minimal pressure impact on aluminium coordination in sodium glasses. Conversely, calcium glasses form higher-coordinated AlO 5 and AlO 6 units under pressure. The determination of non-bridging oxygen (NBO) variation witnesses the change in compensation mechanism for boron species. In low R' glasses, limited NBOs suggest Na + /Ca 2+ release from AlO 4 as the primary compensation source. This work sheds light on pressure's influence on network connectivity in simple glasses, aiding the understanding of complex glass behaviour.