P-31 MAS NMR AND FT IR ANALYSIS OF (50-X 2)NA2O.XBI(2)O(3).(50-X/2)P2O5 GLASSES/

Conventional quenching methods were used to prepare (50-x/2)Na2O.xBi(2 )O(3). (50-x/2)P2O5 system phosphate glasses for x less than or equal to 16.0. The glass structure was then analysed with infrared and P-31 MAS NMR spectroscopy. The main phosphate species formed by the depolym erisation of the sodium metaphosphate chains by Bi2O3 are firstly chai n end groups and then mixed sodium bismuth pyrophosphates. Analysis of the phosphate species shows that some meta and orthophosphates are fo rmed by the equilibrium 2Q(1)=Q(2)+Q(0). Infrared and NMR data are in accordance with the covalent character of Bi-O-P bonds. The stereochem ically active 6s(2) lone electron pair and the high polarisability of Bi3+ lead to a highly distorded coordination sphere, with one sided sh orter covalent Bi-O bonds and longer ionic Bi-O bonds. The former bond s are the origin of the partial glass forming ability of Bi3+.