Effect Of Magnesium Chloride On The Habit Modification Of .

IJSRD - International Journal for Scientific Research & Development Vol. 3, Issue 02, 2015 ISSN (online): 2321-0613Effect of Magnesium Chloride on the Habit Modification of Spectral,Thermal and Nonlinear Optical Properties in KDP CrystalsS. Kumararaman1 T. Thaila2 I. Cicili Ignatius3 T. Raja41P.G Student1,2,3Department of Physics 4Department of Chemistry1Nehru Memorial College, Trichy– 621 007, India 2,3Srinivasan Engineering College, Perambalur – 621212, India 4Trichy Engineering College, Trichy– 621 132, IndiaAbstract— The additive of magnesium chloride withpotassium dihydrogen ortho phosphate (KDP) modifiessome of its spectral, thermal, hardness, linear and nonlinearproperties. The nonlinear optical single crystal of pure andmagnesium chloride added KDP was grown by slowevaporation method. Single crystal X-ray diffraction studyshows that it belongs to tetragonal system. FTIR spectralanalysis was carried out on the material to validate thepresence of functional groups. UV visible spectra wasrecorded for the samples to analyze the transparency invisible and near Infrared (NIR) region. Atomic absorptionstudy reveals the presence of additives in the crystal. Thethermal stability has been analyzed by using TG/DTAstudies. The Microhardness analysis of the grown crystalswas studied. Its nonlinear optical property was tested byusing Kurtz powder method and found to have better SHGefficiency than that of potassium dihydrogen orthophosphate (KDP).Key words: Slow Evaporation Method; Single Crystal XRay Diffraction; Nonlinear Optical Materials, InorganicCompoundsI. INTRODUCTIONThe non-linear optical materials play an important role insecond harmonic generation, optical communications andopto electronics. The search for new frequency conversionmaterials over the past decade has concentrated primarily onorganic compounds [1 & 2] and many organic NLOmaterials with high non-linear susceptibilities have beendiscovered. However the implementation of single crystal,organic materials in practical device applications has beenimpeded by their often inadequate transparency, poor opticalquality and low laser damage threshold. Hence, intenseattention has been paid to inorganic materials showing thesecond order non-linear optical effects because of theirhigher non linearity [3 & 4]. Inorganic materials possessexcellent mechanical, chemical and thermal properties whencompared to organic crystals [5]. In the recent past, therehave been extensive efforts to develop new inorganic,organic and semi-organic materials that possess severalattractive properties such as high damage threshold, widetransparency range and high non-linear coefficient whichmake them suitable for frequency doubling [6 & 7]. KDP isthe most widely used NLO material. It is characterized bygood UV transmission, high damage threshold but still theirNLO coefficients are relatively low. In addition they arealso excellent electro – optic crystals as pocket cells, Qswitches etc. [8 – 13]. Many methods have been tried toincrease the growth rate and improve the NLO properties ofthe KDP crystal [14 & 15]. The addition and their influenceon the growth process and properties of crystals have beentried in recent years [16 & 17]. KDP and ADP are continuedto be interesting materials as they exhibit excellent electrooptic and NLO properties in addition to interesting electricalproperties. The demand for high quality large ADP andKDP single crystals increases due to their application asfrequency conversion crystal in inertial confinement fusion[18].In the present investigation, to enhance the qualityof KDP crystals with better nonlinear optical properties anattempt has been made to grow KDP crystals from theaqueous solution added with magnesium chloride by slowevaporation method at room temperature. The growncrystals have been subjected to single crystal x-raydiffraction, FTIR, optical transmission, thermal, mechanicaland NLO studies.II. EXPERIMENTAL PROCEDUREA. Synthesis:Single crystals of pure KDP and magnesium chloride addedKDP were grown by slow evaporation of the saturatedaqueous solution at room temperature. Analytical reagentgrade (AR) samples of potassium dihydrogen orthophosphate and magnesium chloride were used for thegrowth of single crystals. A solution of potassiumdihydrogen ortho phosphate and magnesium chloride wasprepared in the ratio of 3:1. This solution was heated andleft for evaporation to dryness at room temperature. Thepurity of synthesized salt was increased by successiverecrystallization.B. Growth Procedure:The saturated solution of synthesized salt was taken in abeaker and the solution was filtered twice using borosil filterpaper to remove the suspended impurities. The filteredsolution was taken in a beaker which was tightly closed withthick filter paper so that the rate of evaporation could beminimized. After 30 days the good quality crystals wereharvested(Fig.1 & 2).Fig. 1: Pure KDP CrystalAll rights reserved by www.ijsrd.com1137

Effect of Magnesium Chloride on the Habit Modification of Spectral, Thermal and Nonlinear Optical Properties in KDP Crystals(IJSRD/Vol. 3/Issue 02/2015/287)Fig. 2: Magnesium Chloride added KDP CrystalC. Characterization:The grown crystals of pure KDP and magnesium chlorideadded KDP were confirmed by Enraf Nonis CAD4diffractometer. The functional groups were identified usingPerkin Elmer RXI FTIR spectrometer by KBr pellettechnique in the range of 400 – 4000 cm-1. The opticalproperties of the crystals were examined between 190 and1100 nm using Lambda 35 UV-Vis-NIR spectrometer. Thethermal behaviour of the grown crystals was tested by SDTQ600 V8.3 thermal analyzer. The Microhardnessmeasurements of grown crystals were carried out using aLeitz Weitzler Vicker’s Micro hardness tester with adiamond pyramidal indenter. The NLO property of thecrystal was confirmed by Nd: YAG laser.Fig. 3: FTIR Spectrum of Pure KDP CrystalIII. RESULTS AND DISCUSSIONA. Single Crystal X-Ray Diffraction Analysis:The grown crystals were subjected to single crystal X-raydiffraction analysis to confirm the crystallinity and also toestimate the lattice parameters by employing Enraf NonisCAD4 diffractometer. From the single crystal X-raydiffraction data, it is observed that the grown crystals aretetragonal in structure. The lattice parameters were observedfor the grown crystals and tabulated in Table. 1.MagnesiumParametersPure KDPChloride addedKDPa (Å)7.457.41b (Å)7.457.41c (Å)6.976.94Cell Volume (Å3)387383α (o)9090β (o)9090γ ( o)9090SystemTetragonalTetragonalTable 1: Crystallographic Parameters of Pure andMagnesium Chloride Added KDPB. FTIR Spectral Analysis:The FTIR spectrum of the grown crystals revealed at roomtemperature in the range of400 – 4000 cm-1 is shownin Fig.3 & 4. The O-H stretching band due to water ofcrystallization of KDP is observed at 3941 cm-1.Fig. 4: FTIR Spectrum of Magnesium Chloride Added KDPCrystalIn magnesium chloride added KDP, this peak is shifted to3952.07 cm-1. Similarly, the O-H vibrations of water due toP-OH group pf KDP are observed at 3896 and 3782 cm-1.In In magnesium chloride added KDP, these peaks areshifted are shifted 3838.43 and 3723.98 cm-1. The peakobserved at 3499.78 is attributed to NH2 asymmetricstretching. The O-H stretching hydrogen bonded peakobserved at 3428 cm-1 of KDP is shifted to 3414.02cm-1 inIn magnesium chloride added KDP. The C-H aliphaticstretching band super imposed with NH stretching band ofKDP is observed at 2924 cm-1. This is shifted to 2982 cm-1.The P-O-H symmetric and asymmetric stretching bands ofKDP are attributed to 2844 and 2782 cm-1 respectively. Inmagnesium chloride added KDP, these peaks are shifted to2880.70 and 2780.59 cm-1. The peaks observed at 2462.67and 1641.27 cm-1 are attributed to O P-OH asymmetric andsymmetric bands. The peaks observed at 1301.35, 1104.09and 902.25 cm-1 are attributed to C-N-H, P O and P-O-Hstretching bands. The peaks observed at 542.87 and 454.70cm-1 are attributed to HO-P-OH bending and N-H torsionaloscillation respectively from a comparison of the spectrawith that of KDP [19]. The FTIR spectral band assignmentsare tabulated in Table. 2.Wave number (cm-1)PureMagnesiumAssignmentsKDPChloride added[19]KDP39413952.07O-H stretching due towater of crystallization38963838.43O-H vibrations of water P37823723.98OH groupAll rights reserved by www.ijsrd.com1138

Effect of Magnesium Chloride on the Habit Modification of Spectral, Thermal and Nonlinear Optical Properties in KDP Crystals(IJSRD/Vol. 3/Issue 02/2015/287)--342829243499.783414.022982.82NH2 asymmetric stretchingO-H stretching hydrogenbondedC-H aliphatic stretching28442880.70super imposed27822780.59with NH stretching24642462.67P-O-H symmetric16421641.21stretching13001301.35P-O-H asymmetric10951104.09stretching904902.25O P-OH asymmetric542542.87stretching458454.70O P-OH symmetricstretchingC-N-H StretchingP O StretchingP-O-H stretchingHO-P-OH bendingN-H torsional oscillationTable 2: FTIR Spectral Band Assignments of Pure andMagnesium Chloride Added KDPC. Optical Studies:The optical properties of a material are important, as theyprovide information on the electronic band structure,localized state and types of optical transitions. Fig.5 & 6.show the UV visible spectrum of pure KDP and magnesiumchloride added KDP crystals. From the spectrum, it isobserved that both the pure and magnesium chloride addedKDP crystals show little absorbance in the entire visibleregion. The addition of magnesium chloride seems to haveincreased the crystalline perfection in KDP thereby resultingin lesser absorbance when compared to pure KDP. The cutoff wavelength is around 210 nm for pure and added KDPcrystals. The UV-Vis data reveals that magnesium chlorideadditive improves the optical transparency of the crystal andconfirms the betterment of optical quality.Fig. 5: UV-Vis-NIR Spectrum of Pure KDP CrystalFig. 6: UV-Vis-NIR Spectrum of Magnesium Chlorideadded KDP CrystalD. Atomic Absorption Studies:Atomic absorption spectroscopic (AAS) study formagnesium chloride added KDP crystal was carried toconfirm the presence of magnesium chloride in the lattice ofthe crystal. From this study, it was observed that theconcentration of magnesium chloride is 35.4 ppm. Duringthe growth of magnesium chloride added KDP crystal, itwas observed from AAS study that only low concentrationof magnesium chloride has incorporated into the lattice ofthe magnesium chloride added KDP crystal.E. Thermal Studies:The TG/DTA analysis of the crystal was carried out in airatmosphere at heating rate of 200 C/min. The thermalanalyses give information on the thermal stability, thermaldecomposition and products formed on decomposition. TheTG/DTA curves of pure and magnesium chloride addedKDP crystals recorded in temperature range 25-700o C areshown in Fig. 7 & 8.Fig. 7: TG/DTA Curve of Pure KDP CrystalThe recorded TGA curve of pure KDP exhibitsnegligible weight loss in the region 50 and 200o C. Thedecomposition of pure KDP crystal begins at 230o C andterminates at 350o C. The weight loss starts due to theliberation of volatile substances, probably water molecule ofdecomposed KDP. From the TGA curve of magnesiumchloride added KDP, it is observed that the decompositionstarts at about 230o C and terminates at 370o C which ispossibly due to the decomposition of KDP and remainingmagnesium chloride. It is observed that the crystal of pureKDP is 350o C whereas in magnesium chloride added KDPcrystal the thermal stability increased 370o C. This studyAll rights reserved by www.ijsrd.com1139