Pure and doped triglycine sulfate crystals: growth and characterization

Triglycine sulfate (TGS) crystal is an important ferroelectric crystal used on a large spectrum of radiation detection. Crystals from this family are used as targeted vidicon materials. Pure, (L + D) and L- or D-alanine doped TGS crystals in the ferro- and paraelectric phase, 3-4 cm long, were grown by slow solvent evaporation or temperature reduction. The alanine segregation coefficient, being K approximately 0.01 dopant concentrations in the crystals, was less than 1%. The L- or D-alanine doped crystals presented mirror symmetry and unipolarity. Permittivity and losses were registered online as a function of temperature or at constant temperature versus time (1 kHz, HIOKI, RLC automatic bridge). Essential parameters permittivity, losses, positive and negative polarization components, coercive field components, and the bias field of the doped samples were measured versus temperature. Hysteresis loops and their derivatives were measured with a specially designed Sawyer-Tower device. Generally, doped crystals presented much smaller permittivity and losses and a higher pyroelectric coefficient. Pure TGS samples show nonreproducible permittivity values and its relaxation was studied at constant temperature in the ferroelectric phase. Dielectric parameters have been automatically recorded online every 10 s, during approximately 7 days. It was found that the relaxation time is not a real constant on such large time intervals. In a semi-log scale, permittivity shows three stages, probably related to several mechanisms of relaxation.