Dielectric properties of quenched and x-ray irradiated triglycine sulphate single crystals later excited with laser light

It was reported earlier from this laboratory that, if X-ray or δ-ray irradiated alkali halide crystals were subsequently excited with laser light, interesting changes were observed in their colour centre phenomena and dielectric properties. The results suggested that laser excitation also produces defects in these solids. The work was extended later to other materials. X-ray or γ-ray irradiation of ferroelectrics such as BaTiO3 and KNbO3 showed that the dielectric constant (K) and loss (tan δ) are reduced only at low frequencies. In this letter we present the results of detailed investigations on the effect of X-ray irradiation (and subsequent laser excitation) on the dielectric constant (K) and loss (tan δ) of quenched triglycine sulphate (TGS) single crystals. The frequency range studied was 102-106 Hz and the temperature range 30-80oC. At constant temperature, K decreased with increasing frequency, reaching a constant value at 105 Hz; tan δ also decreased with increasing frequency. The results obtained at different temperatures for a given frequency showed a peak in the value of both K and tan δ at 49oC, the Curie temperature for TGS. An explanation of these observations is offered in terms of the possible lattice defects produced by the laser excitation. (author)