31P MAS NMR and FT IR analysis of (50−x/2)Na2O.xBi2O3.(50−x/2)P2O5 glasses

Abstract

Conventional quenching methods were used to prepare (50-x/2)Na 2 O.xBi 2 O 3 . (50-x/2) P 2 O 5 system phosphate glasses for x≤16.0. The glass structure was then analysed with infrared and 31 P MAS NMR spectroscopy. The main phosphate species formed by the depolymerisation of the sodium metaphosphate chains by Bi 2 O 3 are firstly chain end groups and then mixed sodium bismuth pyrophosphates. Analysis of the phosphate species shows that some meta and orthophosphates are formed by the equilibrium 2 Q 1 = Q 2 + Q 0 . Infrared and NMR data are in accordance with the covalent character of Bi-O-P bonds. The stereochemically active 6s 2 lone electron pair and the high polarisability of Bi 3+ lead to a highly distorded coordination sphere, with one sided shorter covalent Bi-O bonds and longer ionic Bi-O bonds. The former bonds are the origin of the partial glass forming ability of Bi 3+ .