Structural investigation of superionic AgI-containing orthoborate glasses

The structure of superionic glasses of the orthoborate composition xAgI-(1 − x)[0.75Ag2O–0.25B2O3], 0.6 ⩽ x ⩽ 0.9, was investigated by infrared spectroscopy. Transmittance measurements were performed in the range of 30–5000 cm−1 on freestanding flakes prepared by the twin-roller rapid quenching technique. Spectral analysis in the mid infrared revealed a network structure involving trigonal borate units (pyroborate, B 2 O 5 4 - , and orthoborate, BO 3 3 - ) and various tetrahedral borate units, resulting from isomerization and disproportionation chemical equilibria. Addition of AgI to the borate matrix was found to affect the relative abundance of the borate units in favor of BO 3 3 - species. The analysis of the far infrared profiles showed that silver ions occupy oxide and iodide sites, without excluding the presence of mixed oxyiodide sites. The band associated with iodide sites, at ca. 100 cm−1, was found to increase in relative intensity with AgI content and to acquire progressively characteristics resembling those of crystalline AgI for compositions x > 0.78.