Vibrational spectroscopic and bond valence study of structure and bonding in Al sub(2)O sub(3)-containing AgI-AgPO sub(3) glasses

We present a detailed investigation of the effects of synthesis conditions on glasses xAgI-(1 - x)AgPO sub(3) with 0 less than or equal to x less than or equal to 0.4. Raman and infrared spectroscopy of glasses synthesized in platinum crucibles showed that their metaphosphate structure remains largely unaffected by increasing the amount of AgI. This result contradicts recent findings on similar glasses synthesized by melting in alumina crucibles, which were found to exhibit a strongly changing phosphate structure with addition of AgI. The glass transition temperature and ionic conduction properties of the latter glasses also show strong deviation from the analogous properties of glasses melted in platinum crucibles, as in this work. To reveal the origin of such effects, glasses with the nominal composition 0.4AgI-0.6AgPO sub(3) were synthesized in alumina crucibles and their structures were compared with glasses prepared in platinum crucibles with composition yAl sub(2)O sub(3)-(1 - y)[0.4AgI-0.6AgPO sub(3)] and y= 0.0, 0.04 and 0.07. Vibrational spectroscopy showed that melting in alumina crucibles, especially in the presence of P sub(2)O sub(5), leads to doping the AgI-AgPO sub(3) glass with Al sub(2)O sub(3) leached from the crucible. The bond valence approach was employed to assist assigning the new Raman bands that develop when Al sub(2)O sub(3) modifies the metaphosphate structure, with an exponential relationship describing the dependence of the P-O stretching frequency on bond strength. Combination of this relationship with bond valence principles allowed us to associate the formation of aluminum-triphosphate species Al sub(2/3)Ag sub(3)P sub(3 )O sub(10) with the Raman trends observed for AgI-AgPO sub(3) glasses doped with Al sub(2)O sub(3) either intentionally or unintentionally, i.e. when melted in alumina crucibles for long times.