ESR Studies of Radiation-Induced Niobium Centers in Nb2O5–Na2O–SiO2 Glasses

Abstract

Electron spin resonance (ESR) studies have been made of gamma‐irradiated Nb₂O₅–Na₂O–SiO₂ glasses. The samples received a gamma‐irradiation dose of 2 × 10⁷ R at liquid‐nitrogen temperature, and were investigated at that temperature. A broad spectrum which is characterized by an axially symmetric g tensor and hyperfine interaction with the ${}^{93}\mathrm{Nb}\mathrm{(I\hspace{0.17em}=\hspace{0.17em}}\frac{9}{2})$ nucleus, is identified as due to an Nb^4 + center formed in a niobium–oxygen unit. A separate, narrow spectrum located in approximately the center of the broad spectrum can be separated into three distinct spectra: a sharp central spectrum, an asymmetric spectrum on the high‐field side, a 10‐line spectrum. The sharp central and asymmetric spectra are identified as due to two different centers formed in silicon–oxygen units. A hole in an NbO₆ unit is proposed as a model for the 10‐line spectrum.