Ferroelectric properties of pure and doped triglycine sulphate crystal

Permitivity and losses of pure TGS crystal show a peculiar behaviour crossing up and down the Curie point between room temperature and 60 degrees C in two successive runs. The TGS:LD alanine doped crystal show peculiar hysteresis loops, composed of three elementary cycles due to a ''free switching'' component P' and two other non-equivalent components P-A and P-B of opposite directions pinned by dopants. They change their shares in the hysteresis loop versus AC electric field and the pinned components retain up to 20% of the polarisation for pure TGS at saturation. The coercive and the bias fields of the two pinned components show different behaviour both for increasing AC field and temperature, suggesting a nonequivalent alanine substitution in the crystal lattice.