Magnetic resonance studies on radiation-induced point defects in mixed oxide glasses. II. Spin centers in alkali silicate glasses.

Journal Article · Tue Feb 01 04:00:00 EST 2000 · J. Non-Cryst. Solids

DOI:https://doi.org/10.1016/S0022-3093(99)00669-9· OSTI ID:942561

Shkrob, I A; Tadjikov, B M; Trifunac, A D

Irradiation of alkali silicate glasses results in the formation of metastable spin centers, such as oxygen hole centers (OHC{sub 1} and OHC{sub 2}), silicon peroxy radicals and a silicon dangling bond (E' center). In this work, electron paramagnetic resonance (EPR) and electron nuclear double magnetic resonance (ENDOR) are used to study these spin-1/2 defects. It is shown that in a subset of the OHC{sub 1} centers the {triple_bond}SiO radical is strongly coupled to a single alkali cation. Thermally activated swinging motion of this cation causes asymmetric T{sub 2} relaxation and changes electron spin echo envelop modulation (ESEEM) spectra. It is argued that trapping of the hole by non bridging oxygen atoms does not result in the release of a compensating alkali cation. Rather, the O-Alk bond elongates and the whole structure relaxes. This view is supported by semi-empirical and ab initio calculations. The observed axial symmetry of the g-tensor for OHC{sub 2} is the result of rapid tunneling of the electron between two degenerate sites with rate (0.2-50)x10{sup 11} s{sup -1} and activation energy {approx}10 meV. This center is a hole trapped on a tetrahedral >SiO{sub 2}{sup 2-} unit or a planar -SiO{sub 2}{sup -} unit. It is demonstrated that silicon peroxy radicals are not formed by charge trapping. Their generation is temperature-independent and occurs via the decay of self-trapped excitons. It seems likely that the same process yields silicon dangling bond centers.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: SC; EM
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 942561
• Report Number(s): ANL/CHM/JA-32587
• Journal Information: J. Non-Cryst. Solids, Journal Name: J. Non-Cryst. Solids Journal Issue: 1-3 ; Feb. 2000 Vol. 262; ISSN JNCSBJ; ISSN 0022-3093
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

36 MATERIALS SCIENCE
AXIAL SYMMETRY
ELECTRON SPIN RESONANCE
ENDOR
GLASS
IRRADIATION
POINT DEFECTS
RADIATION EFFECTS
RADICALS
RELAXATION
SILICATES