Pure and d:alanina doped triglycin sulphate (TGS) crystals were grown from aqueous solutions in paraelectric phase, by slow solvent evaporation [1]. Fresh cleaved, polished and silver paste painted samples of ~1cm² surfaces and ~1.2 mm thickness were investigated in the -20 ÷ +70 ^oC and 90 Hz ÷ 5 MHz, temperature and frequency ranges. Permittivity e_r and losses, serial and parallel capacity C_s, C_p, serial and parallel resistance R_s, R_p were temperature and frequency investigated using a Hioki 3532-50 type automatic RLC bridge in line with a computer for automatic registering and subsequent processing of the experimental data. Pure crystals show nonreproducible values of the permittivity and dielectric losses crossing up and down the Curie point. More stable and much lower values of the permittivity and dielectric losses could be noticed for the dielectric permittivity of alanina doped crystals as previously shown [2]. The temperature and time evolutions of ferroelectric domains are responsible for this behavior. Both R_s and R_p in the electric equivalent circuit of the crystals shows minima around 49 ^oC, the Curie temperature. Much higher values of R_s, R_p were found for doped crystals due to pined polarization of the crystal induced by the dopant. For pure TGS crystals, losses in the ferroelectric phase show a complicated pattern of time evolution versus temperature. Much smaller and stable values of permittivity and losses, versus temperature and frequency, were found for doped TGS crystals. All investigated parameters show decreasing values with the frequency increase. The experimental results point out for a more stabilized structure with decreased mobility of the dipoles in the structure of the doped versus pure TGS crystals. Thus, higher figure of merit of doped TGS crystals point to a major advantage for technical applications, as IR detectors, gas sensors, thermal imaging devices, etc.

[1] H.V.Alexandru, C.Berbecaru, Cryst.Res. and Technol., 30 (1995) 307

[2] C.Berbecaru, H.V.Alexandru, Mater.Sci.Eng. B 118 (2005) 141

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