Vibrational spectroscopic and bond valence study of structure and bonding in Al2O3-containing AgI–AgPO3 glasses

Abstract

We present a detailed investigation of the effects of synthesis conditions on glasses xAgI–(1 − x)AgPO₃ with 0 ≤ x ≤ 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–0.6AgPO₃ were synthesized in alumina crucibles and their structures were compared with glasses prepared in platinum crucibles with composition yAl₂O₃–(1 − y)[0.4AgI–0.6AgPO₃] and y = 0.0, 0.04 and 0.07. Vibrational spectroscopy showed that melting in alumina crucibles, especially in the presence of P₂O₅, leads to doping the AgI–AgPO₃ glass with Al₂O₃ leached from the crucible. The bond valence approach was employed to assist assigning the new Raman bands that develop when Al₂O₃ 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_2/3Ag₃P₃O₁₀ with the Raman trends observed for AgI–AgPO₃ glasses doped with Al₂O₃ either intentionally or unintentionally, i.e. when melted in alumina crucibles for long times.