ESR STUDIES OF RADIATION-INDUCED NIOBIUM CENTEERS IN NB2O5-NA2O-SIO2 GLASSES

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 93Nb(I = 9/2) nucleus, is identified as due to an Nb4+ 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.