Paramagnetic centers in lithium thioborate glasses

Abstract

Electron paramagnetic resonance spectra have been recorded in the X band 9.5 GHz for B2S3, binary B2S3-nLi2S, and ternary B2S3-nLi2S-pLiI 1 less-than-or-equal-to n less-than-or-equal- to 3, p less-than-or-equal-to 3 glasses. An intrinsic signal without hyper-fine interactions corresponding to about 10 15 spins cm-3 has been detected for 1 less-than-or-equal-to n < 3. Its characteristics lineshape and width, g value of 2.004 are similar whatever the composition. The signal intensity follows a Curie-Weiss law and tends to increase upon thermal treatment of the samples. The electron paramagnetic resonance line vanishes after adding 1 mol% nickel. These arguments, and others, suggest the existence of an intrinsic centre similar to those detected in other sulphur compounds. A tentative description of the defect centre as weakly interacting unpaired spins at end sulphur atoms is formulated. Such a defect is assumed to be due to a very slight excess of sulphur in the glasses and is correlated with the presence of various structural entities believed to exist in the different glass compositions.