Digest Journal of Nanomaterials and Biostructures Vol. 7, No. 3, July - September 2012, p. 1353 - 1364 DIELECTRIC RELAXATION OF TGS CRYSTAL IN THE SECOND ORDER PHASE TRANSITION HORIA V. ALEXANDRU * , CARMEN MINDRU, C. BERBECARU Faculty of Physics, University of Bucharest, Romania Pure triglycine sulphate crystals (TGS for short) undergo a second order phase transition around 49 o C. Peculiar dielectric dispersion of TGS has been noticed walking up and down the temperature through the Curie Point. The dielectric measurements were made on the frequency range 45 Hz  5 MHz, between 65 o C and -150 o C. The Cole-Cole representation of the two- component of permittivity shows two types of relaxation in the ferroelectric phase, crossing down the Curie Point. The temperature and frequency dependence of both components of permittivity was investigated. The slope ratio of the reverse of permittivity in ferro and in paraelectric phase shows a ‘strange’ frequency dependence. An unusual slope change of this ratio was found in the frequency range (1-5)10 5 Hz. This peculiar dependence does not have a straightforward explanation and seems to be for the first time related in the literature. (Received August 14, 2012; Accepted September 6, 2012) Keywords: Triglycine sulphate, permittivity relaxation, dielectric spectroscopy 1. Introduction Ferroelectric TGS crystal has been extensively studied both in pure state and doped. Fundamental ferroelectric properties were earlier studied [1]. Several applications of this crystal have been found as pyroelectric detector in electronics [2], candidate ferroelectric data storage devices (nonvolatile memories) and nanofabrication. These applications require fundamental studies of dynamic and structure domain as well as special studies of polarization switching phenomena, even at the nanoscale Relevant studies have been performed in the field of ferroelectric crystals [3, 4], lattice dynamics [5, 6] and dielectric relaxation [7-9]. Hoshino et al [10] first studied the structure of triglycine sulphate crystals and essential ferroelectric parameters were revealed [11]. We have previously published the growth conditions and properties of pure and doped TGS crystals [12-15]. Zhang had performed Cole-Cole [16] analysis at lower temperatures and carefully around the Curie Point [3, 17]. 2. Experimental Triglycine sulphate crystals were grown from solution, by slow solvent evaporation in a thermostated oven at 52 o C, i.e. in the paraelectric phase. Plates of ~ 1 mm thick were cleaved perpendicular to the b-ferroelectric axis, were grounded, polished and silver electrodes were painted. The TGS sample of about 0.8 cm 2 surface was fitted in a special holder for measurements, placed in a special oven. Heating/cooling of this oven, between RT and 65 o C, was monitored with a constant temperature variation. Cooling down to -150 o C of the sample holder was performed in a special chamber with vapors of liquid nitrogen. In order to avoid water condensation on the * Corresponding author: horia@infim.ro