Effect of ZnSO 4 and MnSO 4 on the Growth of Sulphamic Acid Single Crystals

Single crystals of Sulphamic Acid doped with Zinc Sulphate and Manganese Sulphateweregrown at room temperature using slow evaporation technique. Structural analysis of the grown crystals was done using single crystal X Ray Diffraction and powder X Ray Diffraction studies.Various functional groups seen in the grown crystals are determined using FTIR spectroscopic analysis. The cut-off wavelength of ZnSO4 and MnSO4 doped Sulphamic acid were evaluated by UV-Vis-NIR spectral studies. Thermal behaviour of the grown crystals was identified from Thermogravimetric Analysis (TGA) and Differential Thermogravimetric Analysis (DTA). The mechanical strength and Second harmonic generation of the grown crystals was identified by Vicker’s Microhardness Test and Kurtz powder technique respectively. Article History Received: 12 May 2018 Accepted: 19 July 2018


introduction
In the developing field of laser technology and optical communications, the generation of second harmonics is very essential.The search for new Nonlinear Optical materials and enhancing the properties of existing NLO material is a persistent process due of its wide application in the field of science and technology 1 .When optical waves propagate through Nonlinear Optical crystal, there should be good transfer of energy between the waves.A Nonlinear Optical crystal should have non zero NLO coefficient, transparency at required wavelengths, high physical and optical properties to be used in frequency conversion 2 .Inorganic materials have good chemical flexibility, high thermal and mechanical stability and good transmittance 3 .Among the inorganic materials sulphamate derivatives are most suitable for NLO property with its two planar rings configuration and good blue light transmittance 4 .Sulphamic acid is a highly stable inorganic acid with orthorhombic structure.Its molecular weight is 97.09 1 .It is soluble in water and exhibits zwitterionic form.Large single crystals of pure SA can be grown at low temperatures 5 .Due to these characteristics JIS (Japanese Industrial Standard), IUPAC and British analytical methods committee has accepted SA as a standard substance for titrimetric analysis 6 .The growth, structure, UV-Vis-NIR, neutron diffraction and etching, Raman Studies and dielectric analysis of pure SA single crystal is already reported 1,5,[7][8][9][10] .
Here we report the effect of ZnSO 4 and MnSO 4 in the growth of SA single crystal.
Experimental procedure SA: ZnSO 4 (SAZS) and SA: MnSO 4 (SAMnS) were synthesized by slow evaporation method.Analytical grade chemicals were used for the growth of crystals.Zinc Sulphate (4.036 g/20 ml) and Manganese Sulphate (5.033 g/20 ml) along with Sulphamic acid (3.236 g/20 ml) were prepared by mixing them in the ratio 1: 1 using double distilled water and by stirring the saturated solutions for four hours using magnetic stirrer.The final homogeneous solution of 40 ml is filtered twice using micro sized pore whatman No.1 filter paper in to a separate beaker.The beaker was closed tightly with perforated aluminium foil to minimize evaporation and was kept in a dust free, vibration less environment.Good quality single crystals were grown and reystallization process was carried out to improve the purity of the grown crystals.The photographs of the crystals are shown in figure (1) and (2).

results and Discussion
Single Crystal X-ray Diffraction Single Crystal X-Ray Diffraction is done using BRUKeR AXS KAPPA APeX II CCD using MoKa radiation (λ=0.71073Å) with Shelxtl software.Pure SA and ZnSO 4 have orthorhombic structure 11,12 .When ZnSO 4 is added to pure SA, SAZS crystal has tetragonal structure.MnSO 4 has Orthogonal Structure 13 .When MnSO 4 is added to SA, SAMnS has tetragonal structure.The addition of dopants has changed the crystal structure of SAZS and SAMnS crystals.The lattice parameters of the grown crystals are tabulated in table (1)   powder X ray Diffraction Analysis Powder X Ray Diffraction analysis of SAZS and SAMnS crystals are done using BRUKeR AXS D8 ADVANCe Diffractometer with CuKa (λ=1.5406Ao ) radiation.The grown crystals are crushed into fine powder.The powdered crystals are scanned for 2θ, between 3 degree and 80 degree and shown in Figure (3) and (4).All the observed reflections are indexed.The presence of well defined peaks in the spectrum confirms the high crystallinity of SAZS and  SAMnScrystals 14 .Some extra peaks are observed which are due to the striations in the grown crystals by doping.The change in the intensity of peaks compared to pure SA confirms the incorporation of dopants which had brought changes in the bond length of the grown crystals 5 .

Fourier transform infrared Spectroscopy
Fourier Transform Infrared Spectroscopy identifies the functional groups present in SAZS and SAMnScrystals 15 .It is recorded using THeRMO NICOLeT AVATAR 370 from 500 cm -1 to 4000 cm -1 .
The broad envelope in the region 3750 cm -1 -2970 cm -1 in pure SA is not observed in SAZS and SAMnS 9 .At 1455 cm -1 , the frequency of deformation of NH3+ is identified for pure SA, where as it is seen at 1446 cm -1 for SAZS and SAMnS 16 .The SO 3stretching at 1069 cm -1 in pure SA is moved to 1066 cm -1 for SAZS and SAMnS.Change in the absorption pattern of the grown crystals is due to the presence ofdopants 17 .The recorded spectrum is shown in Figure ( 5) and ( 6).The functional groups present in SAZS and SAMnS crystals are compared with pure SA and recorded in the table (2).
uV-Vis-nir Study C r y s t a l s s h o u l d h ave w i d e t ra n s p a r e n c y window to be used for practical applications   where P is the applied load in kg and d is the average diagonal length of the indentation in mm.A graph is plotted between Hardness number (Hv) and applied load (P) and is shown in Figure ( 13) and ( 14).For SAZS and SAMnS crystals, there is an increase in hardness with load which is due to the work hardening of the surface layer 24 .This proves that these crystals exhibit Reverse Indentation Size effect (RISe).Beyond 100 g, cracking occurs due to the release of internal stresses generated locally by indentation 25 .The increasing value of hardness makes the crystal harder.
According to Meyer's law, the relation between the load and size of indentation is given by p=kd n SAZS, the work hardening coefficient is found to be 13.514 and for SAMnS it is 7.290.According to Onitsch and Hannemann work hardening coefficient 'n' should bemore than 1 and less than 1.6 for hard materials and more than 1.6 for soft materials 28,29 .So the grown crystals are soft materials.

8: uV-Vis-nir Absorption spectrum of SAMnS crystal
Microhardness StudyThe microhardness of SAZS and SAMnS crystals are measured using SHIMADZU MICROHARDNeSS TeSTeR with diamond intender.Loads of magnitude varying from 25 gm to 100 gm is applied for a fixed interval of time over a well-polished grown crystal.The Vicker's Microhardness number Hv is calculated using the relation Hv= 1.8544P/d 2 kgmm-2 SAZS and SAMnS single crystals are grown by slow evaporation solution growth technique at room temperature with aqueous solution.XRD analysis determined tetragonal structure of SAZS and SAMnS crystals.FT-IR analysis confirms the XRD analysis in the form of functional groups present in the grown crystals.Absorption spectrum determines the lower cut off wavelength of 244 nm for SAZS and 213 nm for SAMnS.The presence of dopants has improved the optical property of the grown crystals.Optical studies also confirm the high transparency of SAZS and SAMnS crystals in the visible region.TGA/DTA curves showthat all the grown crystals are thermally stable up to 226 0 C, which is higher thanthe limit for pure SA.Vicker'sMicrohardness test confirms that the grown crystals are soft materials.Hence special care has to be taken during device fabrication using the grown crystals.