An investigation into the relaxation exhibited by glass. Part I. Theory and methods of measurement
JSGT 1957 V41 T350-T382
Theory indicates that glass should exhibit dielectric relaxation phenomena when subjected to low frequency a.c. fields, due to the mechanism responsible for the d.c. anomalous currents. Previous work which has a bearing on this has been briefly reviewed, and it was concluded that further measurements over a wide range of frequencies and temperatures were required. The theory involved and the expected form of the a.c. phenomena are briefly described. Measurements have been made on three simple soda–lime–silica glasses, and on specimens of commercial sheet glass and Pyrex heat-resisting borosilicate glass, in order to determine whether or not glass shows dispersion of its dielectric constant and a peak of dielectric loss of the predicted form. The methods used to determine the dielectric constant and the dielectric loss at frequencies from 100 c/s to 20 kc/s throughout the range from room temperature up to about 400°C are described, a commercial model Schering Bridge and a bridge constructed for the purpose of making measurements at high power factor values being used. The dielectric properties were also measured at room temperature over a range of frequencies from 10 kc/s to 100 Mc/son a commercial dielectric test set. Finally, determinations of d.c. conductivity were made on the same specimens, over the same temperature range as covered by the low frequency measurements. The glasses were shown to exhibit dielectric relaxation phenomena of the expected form. The magnitude of the dispersion of dielectric constant and a value for the energy of activation involved in the process were assessed. The latter was closely similar to the activation energy of the d.c. conduction, suggesting that the movement of the alkali ions was responsible for both phenomena. The form of the dielectric constant and the dielectric loss curves indicated that a wide distribution of relaxation times was involved.
H. E. Taylor
