Growth And Characterization Of Thio Urea Biology Essay

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Single crystal of Thio Urea added L-Histidine have been grown by slow evaporation solution growth technique. Good optical quality single crystal of dimension up to 34x5x8mm3 have been obtained. Single crystal and powder x-ray diffraction analysis, vibrational spectra, thermal measurements and Micro hardness tests have been used to characterize as grown crystals. The optical transmission spectrum and Second Harmonic Generation (SHG) have been studied to find its linear and Non-linear properties. Photoconductive measurement reveals positive photo conducting nature.

Keywords: Crystal Growth, Characterization, Organic compounds, Non Linear Optical materials

1. Introduction

Non Linear Optical(NLO) materials play a vital role in the fields of optical data storage, image processing, electro-optical switching devices, optical information processing and telecommunication. Organic NLO materials have high non linearity and rapid response as compared to organic compounds but they have poor physiochemical stability and thermal stability.

L-Histidine is one of the optically active amino acid having an imiadazole side chain with pKa near neutrality [1]. It acts both as a proton donor and proton acceptor . It also acts as a nucleophilic agent [2].In the present investigation, the growth aspects of TULH have been studied and the bulk crystals were grown by slow evaporation technique. The grown crystals were characterized by single crystal, powder XRD, FTIR, UV-Vis-NIR, TG-DTA analysis, Micro hardness and Photoconductivity measurements. The NLO property of the crystal has also been studied and reported. However, to the authors best knowledge, there is no report about structural parameters of TULH crystals. Therefore, for the first time in this paper, particle size (D), Dislocation density (δ) and Strain values (ε) for corresponding Full width half maximum values (FWHM) are fully reported.

2. Experimental

2.1. Material synthesis

Equimolar ratio of L-Histidine and Thio urea were dissolved in double distilled water and stirred well using a temperature controlled magnetic stirrer at 40 ͦ C to get a homogeneous mixture of solution. Saturated TULH solution was prepared finally and this fully reacted solution was allowed for slow evaporation to get crystalline salt. Highly purified crystalline salt was obtained by doing recrystallization process again and again. Good quality seed crystals were prepared from the crystalline salt. The growth was carried out by slow evaporation method at room temperature with good quality seed crystals. Transparent crystals of size 34x5x8mm3 were obtained in a period of about a week.

3. Results and discussions

3.1. Single Crystal X-ray diffraction studies

Single crystal X-ray diffraction analysis were carried out using ENRAF NONIUS CAD4-F single crystal X-ray diffractometer with MoKα(λ=0.71073Aͦ) radiation. The single crystal analysis data indicates that the TULH crystal belongs to orthorhombic crystal system with space group P21 21 21. Lattice parameters were found to be a=5.14 Aͦ, b=7.33 Aͦ, c=18.61 AÌŠ, α= β= ν =90ÌŠ , Z=4 with cell volume as 701 Aͦ.

TULH values were compared with the crystallographic data of pure L-Histidine crystals [2]. It was found that there was a slight change in the lattice parameters and the cell volume of the crystals. This change may be due to the presence of thiourea in the L-Histidine crystal.

3.2.Powder X-ray diffraction analysis

The grown TULH crystals were crushed into uniform fine powder and subjected to X-ray powder diffraction analysis using monochromated CuKα radiation source (λ=1.540598AÌŠ). The sample was then scanned for a 2θ range 10-70 ͦ at a scan rate of 1 ͦ /min. Miller indices of the planes have been calculated and Bragg's peaks have been indexed and shown in Fig.2. The sharp and well defined peaks confirm the good crystallinity of the grown crystals. Particle size (D), Dislocation density (δ) and Strain values (ε) for corresponding full width half maximum (FWHM) were calculated and listed in the Table 1.

Fig.1 TULH Crystal

Fig.2 Powder XRD of TULH

Fig.1 Powder XRD of TULH

Table 1

Structural Parameters



Particle size(D)


Dislocation density(δ)




















3.3. FT-IR spectral analysis

The Fourier Transform Infrared [3] was carried out between 450 Cm-1 and 4000 Cm-1 using the instrument Perkin Elmer System One FTIR/ATR. Fig.3 shows FTIR spectrum of TULH. In the spectrum, the sharp peak at 3451Cm-1 [4] is the clinching evidence for the protonated form of the Histidine ring nitrogen and NH2 group. C-H asymmetric stretching occurs at 2933 Cm-1. Symmetric bending vibrations of NH3+ are seen at 1490 Cm-1 [5]. It also identifies the symmetric stretching of nitro group[21]. The band at 1064 Cm-1 is due to the presence of antisymmetric stretching vibration in five membered imiadazole ring (C3H4N2)+. The C-C-O stretching and in plane bend gives a peak at 860 Cm-1[6]. The stretching mode of C=S gives a peak at 706 Cm-1 corresponds to the absorption of thio urea[7-9,21]. The peak at 598 Cm-1 is due to the ring in-plane deformation.

Fig.3 FTIR Spectrum of TULH

3.4 UV-Vis-NIR

The UV-Vis-NIR spectrum of TULH is shown in Fig.4 . The spectrum was recorded in the wavelength range 200 to 1000nm using Cary 5E UV-VIS-NIR Spectrophotometer.It is observed that for an entire visible region absorbance is less than 1.5 units and the as grown crystal is transparent in the UV and visible spectral regions of the spectrum. This is a constructive nature of a NLO material[10]. The lower cutoff wavelength was around 310nm and there was no absorption from 350nm to 1000nm which clearly shows that the crystal posses good optical transparency for the second harmonic generation of Nd:YAG laser radiation at 1064nm[11].

The optical band gap of the crystal is determined from Tauc relation[12]. According to this relation a direct band gap material obeys the following relation for high photon energies (hυ)

α= {A(hυ-Eg)n }/hυ …..(i)

where A is a constant. Eg is the band gap of the material and n is an index which can have values ½, 3/2, 2 (or) 3 depending on the nature of the electron transition.

Fig.4. Uv-Vis-Absorption spectrum of TULH

Fig.5 Tauc's plot of TULH

A plot of variation of (αhυ )2 versus hυ is shown in Fig.5 . Eg can be calculated by extrapolating the linear part[13]. The energy gap is of direct type and band gap energy is found to be 3.9eV. The grown crystal is very useful for analyzing the induced polarization due to a wide band gap.

3.5. NLO property

Kurtz SHG test[14] was performed to find the Nonlinear Optical Property(NLO) of TULH crystal. The experiment was performed with Quanta ray series Nd: YAG laser using first harmonics output of 1064nm with a pulse width of 8ns. As grown TULH crystals were grounded into microcrystalline size and the powder was tightly packed between two glass slides . It was then introduced to the light path. The conversion efficiency of TULH crystal was compared with Microcrystalline KDP. The second harmonic signal generated by the crystal was confirmed from the emission of green radiation.

3.6. Thermal analysis

Thermal analysis provide information about the thermal stability of the as grown crystals. This is very important in the point of view of fabrication techniques. The thermo gravimetric analysis of TULH crystals has been carried out between 35̊C to 808.0̊C at a heating rate of 10ͦC/min. The experiment has been performed in nitrogen atmosphere and the TG, DTA plots are as shown in Fig.6. TG curve shows a weight loss starting at about 80̊C.The weight loss in this state is 17.6%. It is followed by two more stages of weight loss between 100ͦC and 280̊C. A major weight loss is present in the range 280 to 380̊C. The weight loss in this stage corresponds to 34%. There is a gradual increase in weight loss if the temperature is increased beyond 380̊C. The total weight loss is about 59% and shows that the stability of the crystal is about 80̊C.

DTA curve shows sharp peak around 84.67ÌŠCwhich is due to water of crystallization. It is followed by two more peaks at 119.94ÌŠC and 204.93ÌŠC which are due to volatization of the compound. The title compound loses its texture at around 80ÌŠC due to the presence of water molecules. It is closely matching with TGA trace.

Fig.6. TG-DTA traces of TULH

3.7. Micro hardness Test

It is used to find the resistance of the material against plastic deformation. Vicker's micro hardness study for TULH crystal is performed on one side of its smooth surface of the crystal with different loads like 25g, 50g, 100g, and 200g. The maximum load is restricted to 200g as micro cracks were developed at higher loads. Fig.7 shows the variation of Vicker's hardness number against applied load. The plot indicates that the hardness of the crystal increases with increase in load and it is in agreement with Reverse Indentation Size Effect(RISE)[15-18].

The relation between load(P) and diagonal length of indentation(d) is given by Mayer's law [19] which is

P = a dn …(ii)

Where a and n are constant for a particular material. Fig.8 shows the variation of log P with log d which is known as Mayer's index number (or) work hardening coefficient(n). The value of n for a TULH crystal is calculated from the graph and it is 3.12684. According to Onitsch, if n > 1.6 that materials are soft materials [20]. Hence, it is concluded that TULH crystal is a soft material.

Fig.7 Variation of Vickers hardness number with load of TULH

Fig.8 Plot of logP versus Log d of TULH

3.8. Photoconductivity studies

Photoconductivity study of TULH crystal was carried out using a KEITHLEY Picoammeter at room temperature. Initially the sample is covered with black cloth to avoid external light radiation and the dark current (Id) was measured for different applied field. The sample is then exposed to 100W halogen lamp containing Iodine vapour and Tungston filament. The corresponding photocurrent (Ip) is measured for same values of applied field. The field dependent photo conductivity of TULH crystal is shown in Fig.9. Dark current of TULH crystal is found to be less than that of Photo current and shows positive photo conductivity.

Fig.9 Variation of Dark and Photo current with applied field of TULH

4. Conclusion

A Non Linear Optical crystal, TULH was successfully grown by slow evaporation method. TG/DTA indicates its thermal stability and suitability in the field of laser application. Optical transparency of the crystal is analyzed from Uv-Vis-NIR spectrum. XRD methods reveals the crystalline nature of the as grown crystal. FTIR analysis confirms the presence of various functional groups in the crystal. SHG efficiency is confirmed by Kurtz powder SHG test. Micro hardness test shows the soft nature of the crystal. Positive photo conducting nature of the crystal is found using Photoconductivity studies.