Available online at www.sciencedirect.com Materials Chemistry and Physics 108 (2008) 170–175 Short communication Growth and characterization studies of ferroelectric diglycine nitrate (DGN) single crystals R. Kanagadurai a,∗ , R. Sankar b , G. Sivanesan a , S. Srinivasan c , R. Rajasekaran d , R. Jayavel b a Faraday Crystal Growth Centre, Department of Physics, R. S. Government College, Thanjavur 613005, India b Crystal Growth Centre, Anna University, Chennai 600025, India c Department of Physics, IIT-Madras, Chennai 600036, India d Department of Physics, Government Arts College, Tiruvannamalai 606603, India Received 1 July 2007; accepted 30 September 2007 Abstract Single crystals of diglycine nitrate [(NH 2 CH 2 COOH) 2 HNO 3 ] (DGN), a ferroelectric material with Curie temperature 206 K, were grown in silica gel at room temperature by the solubility reduction method at room temperature (39 ◦ C). Bulk crystals of dimension 21 mm × 18 mm × 11 mm have been grown by optimizing the growth conditions. The grown crystals have been characterized by structural, optical and mechanical characterization studies. Fourier transform infrared (FTIR) spectral analysis reveals that the crystal consists of all functional vibrational groups. FT-Raman spectrum, which is complement to FTIR studies, has also been recorded. Surface analysis by SEM reveals that the crystal absorbs water from the moisture. The optical transparency range and the lower cut-off of UV transmission were identified from the recorded UV–vis spectrum of DGN. The UV cut-off wavelength of DGN is 286nm. Thermal analysis of the crystalline sample was performed by TGA and DTA methods. The crystal is thermally stable up to 217 ◦ C. The Vicker’s microhardness value of DGN crystal is decreases with increase of load. The work hardening coefficient (n) of diglycine nitrate was determined using the least squares fit method and found to be 1.5. © 2007 Elsevier B.V. All rights reserved. Keywords: Diglycine nitrate; Ferroelectrics; Gel growth 1. Introduction Diglycine nitrate (DGN), bearing the chemical formula (NH 2 CH 2 COOH) 2 HNO 3 , is a significant ferroelectric mate- rial, which belongs to the family of triglycine sulphate (TGS) crystals [1]. DGN crystallizes in monoclinic structure with the order–disorder type ferroelectric transition at Curie tempera- ture, T c , of 206 K [2]. Though the Curie temperature is very low compared to TGS crystal, DGN has been widely stud- ied in order to elucidate the mechanism of phase transition, the configuration of glycine molecules and the nature bonding [2,3]. Studies on spontaneous polarization, dielectric permit- tivity, elastic and electromechanical properties have already been reported on DGN crystals [4]. The anisotropy in opti- cal properties and dielectric properties has also been studied ∗ Corresponding author. Tel.: +91 4362 274984. E-mail address: srkanagadurai@yahoo.co.in (R. Kanagadurai). [5,6]. However, the detailed growth aspects and morphology of the DGN crystals have not been studied. Early attempt was made to grow small crystals by slow evaporation method from aqueous solution useful for property studies [7]. Later, DGN crystals of reasonable size were grown by silica gel method [8]. In the present investigation attempts were made to grow bulk crystals of DGN by optimizing the growth parameters by gel growth method using sodium meta-silicate gel. With the opti- mized pH values, bulk crystals of size 21 mm × 18 mm × 11 mm were grown. Morphology and surface features of the grown crys- tal have been studied. The grown crystals were characterized by powder XRD, FTIR, FT-Raman, UV–vis, thermal analysis and Vickers microhardness studies. 2. Crystal growth The growth of a variety of crystals having immense impor- tance for their practical considerations and theoretical interest has been achieved by gel method [9]. The growth of crystals by 0254-0584/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2007.09.041