http://www.rasayanjournal.com Vol.4, No.2 (2011), 431-436 ISSN: 0974-1496 CODEN: RJCABP SPECTROSCOPIC, THERMAL, OPTICAL, DIELECTRIC AND MECHANICAL PROPERTIES OF THIOSEMICARBAZIDE CADMIUM BROMIDE (TSCCB): A SEMIORGANIC NLO CRYSTAL J. Chandrasekaran 1, P. Ilayabarathi*,2 and P. Maadeswaran 3 1 Department of Physics, Sri Ramakrishna Mission Vidyalaya College of Arts and Science, Coimbatore- 641 020, Tamil Nadu, India. *,2 Research and Development Center, Bharathiyar University, Coimbatore- 641 046, Tamil Nadu, India. 3 Department of Physics, K S Rangasamy College of Technology, Tiruchengode- 637 215, Tamil Nadu, India. *E-mail: ilaya_pj@yahoo.co.in ABSTRACT A new semiorganic nonlinear optical (NLO) crystal, Thiosemicarbazide Cadmium bromide (TSCCB), has been synthesized and good optical quality needle shaped single crystals were grown by slow evaporation technique. The presence of various functional groups was confirmed by FTIR spectroscopic technique. TSCCB was thermally stable up to 205 ºC as determined by TGA/DSC studies and mechanical stabilities have been confirmed by Vicker s microhardness study respectively. The SHG in the grown crystal was identified by modified Kurtz Perry method using Nd:YAG laser with fundamental wavelength of 1064nm. Keywords: Thiosemicarbazide cadmium bromide, Infrared spectrum, Optical transmission spectrum, Thermal analysis and Second harmonic generation. 2011 RASĀYAN. All rights reserved. INTRODUCTION The drive of generating and processing ever increased flows of information has spurred the development of optical fiber communication and related optical signal processing functions 1. Nonlinear optical (NLO) materials are most importance for optical second harmonic generation (SHG) because of their widespread practical applications in high-speed information processing, optical communications, and optical data storage, optoelectronics and photonics 2. Hence the inorganic NLO materials are having good mechanical strength but less nonlinear optical coefficients. Organic NLO materials are showing better performance in NLO properties but poor mechanical behaviour and thermal stability. Considering these properties, crystal growers have found a new class of materials called semiorganic nonlinear optical crystals formed by organic acids with inorganic materials possess the combined advantages in NLO applications is due to crystallize in noncentrosymmetric space groups and the favorable mechanical and thermal properties of inorganic solids 3. In this respect, thiosemicarbazide and its derivates are interesting materials for NLO application. Thiosemicarbazide cadmium chloride monohydrate (TCCM) are some of the examples which proved their applications in the field of NLO and having second harmonic generation (SHG) efficiency greater than KDP 4,5. In this present work, a systematic investigation has been carried out on the growth of TSCCB subjected to fourier transform infrared spectroscopy, optical transmission, thermal stability, dielectric constant, microhardness and second harmonic generation efficiency studies. Synthesis and growth technique The starting materials were highly pure and the synthesis and growth process were carried out in aqueous solution. Thiosemicarbazide cadmium bromide (TSCCB) has been synthesized by taking
cadmium bromide and thiosemicarbazide in a 1:1 stoichiometric ratio. The crystal was synthesized according to the following Eq. (1). CdBr 2 +NH 2 -NH-CS-NH 2 Cd (NH 2 -NH-CS-NH 2 ) Br 2 (1) The calculated amount of cadmium bromide was first dissolved in deionized water. Then thiosemicarbazide was added to the solution slowly. The solution was agitated with a magnetic stirring device and filtered after complete dissolution of the starting materials. The prepared solution was left standby for several days at room temperature; thereby colorless crystals were obtained in 25 days shown in Fig.1. Characterizations The Fourier transform infrared spectrum was recorded by the KBr pellet technique using Thermo Nicolet V-200 FT IR spectrometer to confirm the vibrational structure of the crystalline compound with scanning range of wave number 4000-400 cm -1. The thermal behavior of grown sample was studied by using Q600 SDT and Q20 DSC model. The dielectric permittivity of TSCCB crystal was studied by using Agilent 4284 A Precision LCR meter at room temperatures to 150 C in the frequency range 20Hz-1MHz. The mechanical property of the grown crystal was studied using HMV 2T microhardness testor. The detailed discussions on the obtained results are presented in the following sections. RESULTS AND DISCUSSIONS FTIR studies The Fourier transform infrared analysis was carried out between 4000-400 cm -1 by recording the spectrum using Thermo Nicolet V-200 FT IR spectrometer by KBr pellet technique shown in Fig.2. The broad envelope positioned between 3289 and 3168 cm -1 corresponds to the asymmetric and symmetric stretching vibrations of NH 2 group 6. The NH 2 bending 1641 cm -1, vibrational mode was almost observed in the same frequencies as in thiourea, suggesting that the nitrogen to metal bond is not present in the coordination complex. The absorption at 1562 cm -1 is due to N-C-N asymmetric stretching. The symmetric and asymmetric stretching of C=S are observed at 1457 and 748 cm -1 respectively. A peak at 683 cm -1 is due to the C-Br stretching. The assignments confirm the presence of various functional groups present in the material, tabulated in Table 1. From the following observations the presence of the specific groups are confirmed with the spectra of thiourea 7. Thermal analysis The thermal stability of TSCCB was identified by the thermogravimetric analysis (TGA) and differential scanning calorimetory (DSC). The thermal analyses were carried out using the model Q600 SDT and Q20 DSC instruments. The TGA and DSC thermogram of TSCCB was investigated and is shown in Fig.3. A crucible was used for heating the sample and analyses were carried out in an atmosphere of nitrogen at a heating rate of 20 K/min in the temperature range 0-800 C. The TSCCB sample weighing 25.9 mg was taken for the analysis. The most important and interesting thing noted was the very good thermal stability up to 205 C. The TG curve shows the corresponding weight loss in various stages 8. In DSC an exothermic peak noticed at 205 C corresponds to the melting point of TSCCB. Furthermore, it indicates that there is no phase transition before melting. A systematic weight loss was observed as the temperature further increases above the melting point. It is also noticed that total decomposition of the compound takes place at a temperature above 800 C. Dielectric Study The dielectric study on TSCCB single crystal was carried out using the instrument, AGILENT 4284 A (20Hz-1MHz) Precision LCR Meter for various frequency with function of temperature. The prepared sample was heated from room temperature to 150 C and capacitance and dielectric loss of the sample was measured by varying the frequency from 100Hz to 1MHz. From the graph (Fig.4) the dielectric constant decreases with increased frequency 9. The very high value of dielectric constant (ε r ) observed at low frequencies, which may be due to the presence of all the four polarizations namely; space 432
charge, orientation, electronic and ionic polarization and its low value at higher frequencies may be due to the loss of significance of these polarizations gradually. The characteristic of low dielectric constant with high frequency for a given sample suggests that the sample possess enhanced optical quality with lesser defects and this parameter is of vital importance for various NLO materials and their applications 10. Microhardness studies The microhardness studies were carried out using HMV 2T, Vicker s microhardness tester to determine the mechanical strength of the grown TSCCB single crystal shown in Fig.5. The static indentations were made at room temperature with a constant indentation time of 15 s for all indentations. The indentation marks were made on the surfaces by varying the load from 5 to 100g. The hardness is generally measured as the ratio of applied load to the surface area of the indentation. The grown crystal with smooth and dominant face was selected for microhardness studies. Indentations were carried out using Vicker s indentor for varying loads (5 100g), for each load, several indentations were made and the average value of diagonal length was used to calculate the microhardness. Vicker s microhardness number was determined using Hv=1.8544 P/d 2 kg/mm 2. The hardness number was found to increase with the load up to 75g and after a load of 75g, Hv suddenly decreases as cracks developed in the material 11. This may be due to the release of internal stresses generated locally by indentation. Nonlinear optical studies Nonlinear optical property of the crystal was determined by the modified version of powder technique developed by Kurtz and Perry 12, 13. The crystal was ground into fine powder and packed in the micro capillary tube. A Q-switched Nd:YAG laser (1064 nm) has been used. The input pulse energy of 3.2 mj/pulse and pulse width 8ns was incident on the crystalline powder. The SHG signal at 532 nm is detected using a photomultiplier tube (PMT). The generation of the second harmonics was confirmed by the emission of green radiation. The present result shows that SHG conversion efficiency of KDP is 105 mv and for TSCCB is 198 mv. CONCLUSION Thiosemicarbazide cadmium bromide, a new semiorganic material has been synthesized by solvent evaporation technique at room temperature. The FT IR analysis verified all the functional groups and molecular strength of the crystal. TGA/DSC analysis indicated that crystals are stable up to 205ºC, suggesting that it has higher thermal stability. From the micro hardness investigations the grown crystal has minimum surface hardness about 75 kg/mm 2. The variation of dielectric constant was studied with ranging frequency at room temperature. The Kurtz powder second harmonic generation test shows that the crystal is a promising candidate for optical second harmonic generation applications. Acknowledgments- The authors thank sophisticated analytical Instrumentation facility (STIC), Cochin and Central Electrochemical Research Institute, Karaikudi for the help. The authors are grateful to Prof.P.K.Das, IISc., Bangalore for extending the facilities to measure SHG efficiency. Fig.-1: As-grown TSCCB crystal. 433
Fig.-2: FT IR Spectrum of TSCCB crystal. Fig.-3: TGA/DSC Curve of TSCCB crystal Table-1: FTIR spectral data of TSCCB crystal 434
Wavenumber (cm-1) Assignments Thiourea TSCCB 3280 3289 Asymmetric NH 2 stretching 3167 3168 Symmetric NH 2 stretching 1627 1641 NH 2 bending 1593 1562 Asymmetric N-C-N stretching 1472 1457 Asymmetric C=S stretching 1089 1079 Asymmetric N-C-N stretching 740 748 Symmetric C=S stretching 648 683 C-Br stretching TSCCB 25 Dielectric Constant(εr) 20 15 10 5 0 40 50 60 70 80 90 100 110 120 130 140 150 Temperature(ºC) 100Hz 1KHz 10KHz 100 KHz 1MHz Fig.-4: Dielectric Constant of TSCCB crystal. TSCCB 75 60 Hv(Kg/mm2) 45 30 15 0 5 25 50 75 100 Load(P) Fig.-5: Microhardness of TSCCB crystals 435
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