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Modification of Ferroelectric Properties of TGS Crystals Grown under a dc Electric field G. Arunmozhi1, E. Nogueira1, E.de Matos Gomes1, S. Lanceros-Mendez1, M. Margarida R. Costa2, A. Criado3 and J. F. Mano4 1 Departamento de Física, Universidade do Minho, Campus de Gualtar 4710-057 Braga, Portugal. 2 Departamento de Física, faculdade de Ciências e Tecnologia, Universidade de Coimbra, 3000 Coimbra, Portugal. 3 Departamento de Física de la Materia Condensada, Universidad de Sevilla, Apartado 1065, 41080 Sevilla, Spain. 4 Departamento de Engenharia de Polímeros, Universidade do Minho, Campus de Azurém 4800-058 Guimarães, Portugal.

ABSTRACT Ferroelectric triglycine sulphate crystals have been grown under the influence of an intense electric field of 6x104 V/m. Relative to crystals grown under ambient conditions (TGS) the crystals grown under the electric field (TGS-E) display a dielectric permittivity a factor of two lower. Significant differences are observed in the Curie-Weiss behavior of the ferroelectric phase, in the x-ray diffraction patterns and in the differential calorimetry measurements. INTRODUCTION Ferroelectric triglycine sulphate (NH2CH2COOH)3.H2SO4), (abbreviated TGS) was discovered by Mattias et al. [1] in 1956. It exhibits a second order phase transition with the Curie temperature at 49°C. Below and above the Curie point, the crystal has monoclinic symmetry. In the paraelectric phase (T > 49ºC), it belongs to the centrosymmetrical crystal class 2/m and in the ferroelectric phase (T < 49ºC) the mirror plane disappears and the crystals belongs to the polar point group 2 [2]. TGS can be grown in large sizes from aqueous solutions. The growth can be achieved by slow evaporation of the solvent at constant temperature or by slowly lowering the temperature at constant supersaturation. Single crystals of triglycine sulphate (TGS) find wide application in pyroelectric detection. Depolarization of the glycine molecule with time in TGS seriously affects the device performance. Several dopants have been reported to stabilize the glycine molecule. Depolarization fields can be overcome if an internal bias field is created in the TGS lattice [3, 4]. In this paper we report preliminary results on the dielectric, structural ,SEM and thermal behaviour of TGS grown under a high dc electric field of 6.0x104 V/m. To the best knowledge of the authors, no work has been reported in the literature on the effect of high dc fields applied during crystal growth. EXPERIMENTAL DETAILS Crystals of TGS were obtained by re-crystallizing a water solution under a dc electric field of roughly 6.0x104 V/m. The electric field was generated by using a transformer to create a galvanic isolation as well as to provide an initial increase of the voltage. Subsequently a chain of voltage multipliers were used to both amplify and rectify the ac voltage source into a high dc voltage allowing GG3.5.1

us to eventually reach a differential of up to 40 kV. Rectangular glass cells containing the solution were then placed between condenser plates, th