Synthesis, growth and characterization of non linear optical Bisthiourea ammonium chloride single crystals by slow evaporation technique E. Ilango a , R. Rajasekaran b , K. Shankar a , S. Krishnan c , V. Chithambaram d,⇑ a Research and Development Centre, Bharathiyar University, Coimbatore 641 046, India b Department of Physics, Government Arts College, Tiruvanamalai 606 601, India c Department of Physics, B.S Abdur Rahman University, Vandalur, Chennai, India d Research Centre Physics, Dhanalakshmi College of Engineering, Chennai 601 301, India article info Article history: Received 21 May 2014 Received in revised form 18 August 2014 Accepted 19 August 2014 Available online 7 October 2014 Keywords: A. Crystal growth B. Nonlinear optics C. X-ray diffraction abstract A new semi-organic nonlinear optical crystal of Bisthiourea Ammonium Chloride (BTAC) has been grown by slow evaporation technique. The crystal system and lattice parameters were determined from X-ray diffraction. Fourier Transform Infrared (FTIR) studies confirm the various functional groups present in the grown crystal. The transmittance and absorbance of electromagnetic radiation is studied through UV–Visible spectrum. The thermal behavior of the grown crystals has been investigated by TG/DTA anal- ysis. The dielectric constant and dielectric loss has been studied as a function of frequency for various temperatures and the result were discussed in detail. The SEM analysis was also done and it revealed the surface morphology of BTAC crystal. The second harmonic generation has been confirmed by the Kurtz powder test and it is found to be 1.4 times more than that of KDP crystal. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction In recent years, second order nonlinear optical materials have attracted many researchers because of their potential applications in various emerging technological fields [1–7]. Today, crystal growth technology has advanced rapidly for the development of novel non- linear optical materials (NLO) for various applications such as optical switching, frequency conversion and electro-optical modulation [8– 13]. The organic NLO materials have large nonlinear optical coeffi- cients compared to inorganic material, but their use is impeded by their poor mechanical and thermal properties and low laser damage threshold [14]. The inorganic NLO materials have excellent mechan- ical and thermal properties but possess relatively modest optical nonlinearities due to lack of extended p-electron delocalization [15]. In view of these problems, a new class of materials has been developed from organic and inorganic complexes called semi organic [14,16]. In these materials, high optical nonlinearity of pure organic compound is combined with the favorable mechanical and thermal properties of inorganic materials [14–18]. Semi organic crystals have large damage threshold, wide transparency range, less deliquescence, excellent nonlinear optical coefficient, low angular sensitivity and exceptional mechanical properties [19,20]. In the present work, semi organic nonlinear optical crystal Bis- thiourea Ammonium Chloride (BTAC) is the first time grown from aqueous solution using slow evaporation technique. The grown crystals were subjected to various characterizations such as single crystal X-ray diffraction analysis, Fourier Transform Infrared (FTIR) analysis, optical absorption studies, dielectric studies, Scanning Electron Microscope and nonlinear optical studies and were dis- cussed in detail. All the studies shows, this crystal is high efficient NLO crystal. 2. Experiment 2.1. Crystal growth Single crystals of BTAC were grown by dissolving (AR Grade) Thiourea and (AR Grade) ammonium chloride in the ratio 2:1 using double distilled water. The synthesized salt was again dissolved in Millipore water and then recrystallized by slow evaporation process at constant room temperature. Extreme care was taken to minimize the thermal and mechanical disturbances to the supersaturated solution. After recrystallisation and filtration, optically good quality crystals were obtained within a period of 4 weeks. The grown crystal BTAC is shown in Fig. 1. 2.2. Solubility The solubility of BTAC was determined for five different tem- peratures namely 32, 35, 40, 45 and 50 °C. The solubility was deter- http://dx.doi.org/10.1016/j.optmat.2014.08.011 0925-3467/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +91 44 27178366; fax: +91 44 27178365. E-mail address: chithambaramv@gmail.com (V. Chithambaram). Optical Materials 37 (2014) 666–670 Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat