TRIGLYCINE SULPHATE DYNAMICS OF DOMAINS IN RELATION WITH TEMPERATURE AND BIAS FIELD

Triglycine sulphate crystal (TGS) is a hybrid organic-inorganic ferroelectric crystal with a large electronic band-gap, transparent in visible spectra. It has large applications in electronics, as thermal IR detector. Pure and doped TGS crystals of 3-5 cm linear dimensions were grown at constant temperature in the paraelectric phase (52 oC), by slow solvent evaporation. Pure TGS samples show non-reproducible values of permittivity and losses in the ferroelectric phase after the “excursion” in the paraelectric phase. Walking up and down the crystal temperature, using a special program, the permitivity and losses were automatically recorded and analyzed. There is a continuous decrease of permittivity towards an equilibrium value during a long period of time. Previous AFM measurements from the literature have revealed peculiar aspects of domain dynamics. The relaxation process of permittivity was considered according to the equation er = A - B exp(-t/t). However, surprisingly, there is not a unique relaxation time t. For the first 500 sec (or so), the relaxation time is t » 7 minutes, while between the next time decades 1.000 - 10.000 - 100.000 sec, it is approximately 1 hour and 8 h respectively. The process is related with the ferroelectric domain’s dynamics, which are more or less strongly pined by dislocations or some other lattice defects.