Investigation on Zn (II) Doped Lithium Sulphate Monohydrate Single Crystals 45

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1 Investigation on Zn (II) Doped Lithium Sulphate Monohydrate Single Crystals 45 E. Glitta Sumangali 1, Girish M. Joshi 2 1 Department of Physics, VIT University, Vellore , Tamilnadu, India 2 Material Physics Division, VIT University, Vellore , Tamilnadu, India DOI /mmse provided by Seo4U.link Keywords: crystal growth, XRD technique, FTIR, optical studies, EDAX. ABSTRACT. Zn-doped Lithium Sulphate monohydrate single crystals with good quality were grown by slow evaporation technique. The grown crystals were subjected to powder X-ray diffraction study that confirms the change in the lattice parameters and quality of the crystal, Fourier Transform Infrared Spectroscopy ensures the functional groups, UV-Visible analysis which reveals the optical transmittance, lower cut-off wavelength and band gap, and Energy dispersive X-ray analysis gives chemical composition and confirms the inclusion of the dopant into the grown pure LSMH single crystal. Introduction. The investigation of NLO materials have gained predominant attention in current research owing to their applications in the technology of information transmission and processing. It is evident that the NLO crystals have exceptional technological requirements such as wide transparency range, fast response and high damage threshold. Due to such distinct optical properties, synthesis and growth of unique materials are in progress. The most widely used materials in photonic technologies are mainly inorganic crystals based on Borates and Phosphates. Lithium Sulphate Monohydrate Li2So4H2o (LSMH) is also one such inorganic highly NLO active materials [1-4]. The crystal structure and space group of Lithium Sulphate Monohydrate were originally determined as monoclinic point group P21 by G.E.Ziegler (1934) [5]. A detailed study on the redetermination, further refinement and inclusion of hydrogen s position of Li2So4H2o structure were reported [6-8]. It is explored from the literature that the Lithium Sulphate Monohydrate has remarkable piezoelectric and electro-optic properties. Lithium Sulphate Monohydrate has highest pyroelectric effects among the non-ferroelectric polar crystals [9]. Earlier researches show that Lithium found to be effective NLO material on its combination with Selenate, Glycine and Bromide [10-12]. Since there is large demand for crystal in electronic industries, it is required to synthesize NLO material and to improve the properties of existing materials. Considering the facts, ethylene diamine tetra acetate and Cu II doped Lithium Sulphate Monohydrate single crystals have been synthesized and shown as promising candidate for optical second harmonic generation [13-14]. In the present work attempts have been made to enhance the physical properties of single crystals by incorporating bivalent metal dopant. The presence of very low concentration of suitable additives enhances crystalline perfection [14]. Therefore, we present the Synthesis of grown Lithium Sulphate monohydrate single crystals containing 0.1 mole percentage of Zinc Sulphate by slow evaporation method. The lattice parameters of doped crystals are evaluated by powder X-Ray diffraction study, Optical analysis and the presence of Zn has been determined by Energy dispersive X-ray analysis. Experimental. Single crystals of pure and Zinc doped Lithium Sulphate Monohydrate (LSMH) were grown at room temperature by the reaction between Lithium Sulphate Monohydrate and Zinc Sulphate and dissolving 0.9 mol % of Li2So4H2o (LSMH ) with 0.1 mol % of ZnSo4.7H2O in double 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license

2 distilled water. The solution was continuously stirred well for long time using a magnetic stirrer to ensure homogenous solution. The completely dissolved solution was filtered using Wattman filter paper to remove the suspended impurities and allowed to yield crystalline by slow evaporation of solvent. The solution was allowed to evaporate at room temperature, tiny seeds were observed within 15 days and good quality pure and doped crystals were collected after 30 days. The grown pure and doped crystals are shown in fig.1 that posses already reported crystallography-dependent shape confirmed by chemical bonding theory of crystal growth [15]. Fig. 1. Photograph of pure LSMH crystal. Fig. 2. Photograph of Zn doped LSMH crystal. Characterization Techniques Powder X-Ray Diffraction. Powder X-ray diffraction study on doped LSMH crystal grown by slow evaporation technique was carried out. The crystalline nature and the lattice parameters were confirmed by powder XRD. Powder XRD pattern was recorded for the grown crystals using BRUKER and shown in fig.3. The results were compared with the JCPDS database [16] where the prominent peaks of the reported values coincided with the investigated patterns. The sharp and intense peak on the pattern indicates that the crystallities are pure and dislocations free [17].By using the observed 2θ and d values from the powder XRD pattern, the hkl indices and lattice parameters were calculated. The values are a= å, b= Å, c= Å. It is apparent that the grown Zn doped crystal also has the monoclinic system, however, the incorporation of the metal ion in LSMH pronounced slight changes in the lattice parameters. Fig. 3. XRD pattern of Zn-LSMH crystal

3 FTIR Spectrum Analysis. The FTIR analysis of LSMH and ZnSo4 doped LSMH were carried out between 400 cm cm -1 usinjg Perkin Elmer Spectrum II. The FTIR spectrum of LSMH and Zn doped LSMH was shown in fig.3. From the spectrum it is evident that peak values clearly shows that the presence of LSMH in grown crystals. From the spectrum the So4 - stretching bands are generally superimposed near 1114 cm -1. An intense sharp peak at 1613 cm -1 is due to the bending vibration mode of H2O. The sharp peak at 654 cm -1 indicates the presence of sulfate ion. The spectra show the presence of H2O molecule and O-H symmetric stretching at 3490 cm -1. FTIR assignments on the grown crystals were given in below table. Table 1. Wavelength and Assignments of LSMH and Zn-LSMH. Pure LSMH (cm -1 ) Zn doped LSMH (cm -1 ) Assignments Presence of water molecule (O-H Symmetric Stretching) Bending Vibration mode of H2O Presence of Sulphate 654 Presence of Sulphate ion Fig. 4. FTIR spectrum of LSMH and Zn-LSMH crystals. UV-Visible Spectrum Analysis. UV-visible- NIR spectroscopic analysis is very important for any optical material because an optical material can be of practical use only if it has a wide transparency window. To record the transmission data Varian Cary 50 bio UV- visible- NIR spectrophotometer in the wavelength region nm at ambient temperature with high accuracy was used. The recorded data was used to calculate the optical transparency, band gap of the grown crystals. The Transmission spectrum of LSMH and Zn doped LSMH as shown in fig.4. The cut off wavelength of pure LSMH was found to be 213 nm and Zn doped LSMH was found to be 249 nm. The bandgap of pure LSMH and Zn doped LSMH were found to be 5.8 ev and 4.9eV respectively

4 EDAX Analysis. Quantitative EDAX analysis is the most commonly used method for chemical analysis of materials. The elemental analysis was carried out using GENESIS The EDAX spectrum of Zn doped LSMH is displayed in Fig.5.which illustrates the characteristic peaks corresponding to the binding energy state of S, O and Zn. The incorporation of Zn in lithium sulphate monohydrate was confirmed in this analysis. It is to be mentioned here that lithium cannot be identified from the sample by EDAX method for the obvious reason that the X-ray fluorescence yield is extremely low for Li [18-19]. Fig. 5. UV Transmittance spectrum and of LSMH and Zn-LSMH crystals. Fig. 6. EDAX spectrum of Zn doped LSMH single crystal. Summary. Single crystals of Zn doped lithium sulphate monohydrate has been grown by slow evaporation technique. Powder XRD study substantiate the crystal perfection with monoclinic crystal structure point group P21.FTIR spectrum confirms the functional groups of the grown crystals. The less optical absorption in the visible region and decreased band gap were studied. Using EDAX analysis presence of dopant was ensured. All these studies reveal that the presence of bivalent dopant enhances the crystal quality. References [1] Fang Kong, Shu-Ping, Zhong-Ming,Jiang-Gao Mao and Wen-Dan Cheng, A new type of secondorder NLO material, J.AM.CHEM.SOC, China, 2006, 128,

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