Deciphering vanadium redox and structure in aluminosilicate glass: A spectroscopic study

Abstract

Vanadium oxide can be used to color silicate glasses and to influence their crystallization behavior. However, vanadium’s role in glass is strongly dependent on its redox state and local structure, both of which are poorly understood. In this study, XANES, Raman and optical absorption spectroscopy were used to determine vanadium redox state in an aluminosilicate glass. Raman spectroscopy of oxidized and reduced samples allowed for the attribution of the Raman signatures of vanadium ions. The species present in the glass synthetized under air are [V⁵⁺O₅]^5-, [V⁵⁺O₄]^3- and [V⁴⁺O₅]^6-. When the glass is synthetized under reducing conditions, the redox state is a mixture of V³⁺ and [V⁴⁺O₅]^6-. Our results show that optical absorption spectroscopy is well-suited to monitor changes in V⁴⁺ concentration, while Raman spectroscopy allows the monitoring of V⁵⁺. Vanadium reduction mechanism was investigated by performing Raman and optical absorption spectroscopy measurements along a reduction profile. Our results show that V³⁺, V⁴⁺ and V⁵⁺ coexist over a range of oxygen fugacity. This leads to sample color not being linear with oxidation state as the coexistence of V³⁺ and V⁵⁺ might be responsible for the rise of another optical absorption that darkens the glass.