Vibrational spectroscopy study of niobium germanosilicate glasses

A series of glasses in the (Ge,Si)O2–Nb2O5–(Na,K)2O system were prepared by melting and casting. Their density and characteristic temperatures were determined by Differential Thermal Analysis (DTA) and their structure was analyzed by infrared and polarized Raman spectroscopies. DTA data have indicated an increased glass thermal stability with the replacement of GeO2 by SiO2. Kramers–Kronig analysis of the infrared specular reflectance data indicated a strong ionic character for the germanosilicate glasses. The Raman spectra of germanosilicate compositions were generally dominated by an intense Boson peak at ∼72 cm−1 and a high frequency, polarised peak at ∼880 cm−1, related to NbO6 octahedra with at least one non-bridging oxygen. The germanosilicate structure appears to be formed by alternating GeO4 tetrahedra and NbO6 octahedra, in addition to SiO4 tetrahedra.