Unidirectional growth of α‐NiSO4·6H2O crystal by Sankaranarayanan–Ramasamy (SR) method

Large cylindrical [001] direction α‐nickel sulphate hexahydrate crystal with 20 mm diameter and 140 mm length was grown from an aqueous solution by uniaxially solution‐crystallization method of Sankaranarayanan–Ramasamy (SR). The grown crystal was examined by X‐ray diffraction, UV‐Vis‐NIR spectroscopy and TGA/DTA analysis methods.     

Growth of α-NiSO<Subscript>4</Subscript> · 6H<Subscript>2</Subscript>O crystals at high rates

The high-rate growth of nickel sulfate hexahydrate NiSO₄ · 6H₂O (α-NSH) crystals up to 120 × 120 × 65 mm³ in size is described for the first time. The data on the distribution of related impurities in the {011} and {001} growth sectors of α-NSH crystals grown at different rates are reported. The transmission spectra of both growth sectors of these crystals are obtained. The structural quality and the optical properties of rapidly and slowly grown α-NSH crystals are compared. It is established that the {011} growth sector of crystals grown at rates exceeding 5 mm/day shows the best characteristics for application in UV filters.     

Gel growth of α and γ glycine and their characterization

The microbial free single crystals of α and γ glycine were grown from gel at room temperature in a new chemical route. These crystals showed a superior quality than the solution grown crystals. The metastable α-form and the stable γ-form of glycine were crystallized in silica gel by solubility reduction method. The form of crystallization is confirmed by single crystal and powder X-ray diffraction analyses. The crystals of α and γ glycine were found to crystallize in monoclinic and hexagonal crystal systems, respectively. For analyzing the functional group and thermal stability of α and γ glycine crystals, spectroscopic and thermal analyses have been carried out. The dielectric studies were performed to find the dielectric constant of the grown crystals and the results are discussed. Second harmonic generation efficiency of the crystal was measured by Kurtz’s powder method using Nd:YAG laser and it was found to be 2.68 times that of potassium dihydrogen phosphate crystals.     

Studies on conventional and Sankaranarayanan–Ramasamy (SR) method grown ferroelectric glycine phosphite (GPI) single crystals

Transparent single crystals of glycine phosphite were grown by Sankaranarayanan–Ramasamy (SR) method and conventional slow evaporation solution technique (SEST) which had the sizes of 100 mm in length, 30 mm diameter and 10×11×8 mm³. The conventional slow evaporation and Sankaranarayanan–Ramasamy method grown glycine phosphite single crystals were characterized using laser damage threshold, chemical etching, Vickers microhardness, UV–vis–NIR and dielectric analysis. The laser damage threshold value was higher in SR method grown GPI crystal as against conventional method grown crystal. The SR method grown GPI has higher hardness and also higher transmittance compared to conventional method grown crystal. The chemical etching and dielectric loss measurements indicate that the crystal grown by SR method has low density of defects and low value of dielectric loss compared to conventional method grown GPI crystal.     

Crystal growth,optical, mechanical and electrical properties of organic NLO material γ‐glycine

Single crystals of organic non‐linear optical material, γ‐glycine have been grown by gel method for the first time. The γ‐phase is confirmed by single crystal XRD. The presence of various functional groups of γ‐glycine are confirmed by FTIR. The UV‐Vis‐NIR spectrum reveals the high percentage of transmission of the sample in the entire visible region. The SHG of γ‐glycine is confirmed by Kurtz powder technique. TGA‐DTA studies indicate that the crystal is structurally stable upto 170 °C. Microhardness investigations are conducted on the grown crystals. The dielectric constant measurements are carried out and the nature of variation of dielectric constant ε′ and dielectric loss D in the frequency range of 50 Hz to 5 MHz is studied and reported. Photoconductivity studies of γ‐glycine crystals revealed the negative photoconducting nature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of TGS crystals using uniaxially solution‐crystallization method of Sankaranarayanan‐Ramasamy

The recently discovered crystal growth method called uniaxially solution‐crystallization method of Sankaranarayanan–Ramasamy (SR) is modified in some aspects and used for growth of triglycine sulphate (TGS) crystals. The modification leads to the simplicity, reduction of cost and avoided the temperature fluctuations. The 〈010〉 direction of TGS is very important and used for fabrication of infrared detectors. Using this method, the 〈001〉, 〈010〉 directional crystals of TGS were successfully grown in a glass crystallizer. The grown crystal was characterized by HRXRD, UV‐Visible and dielectric studies. The results prove the suitability of the modified SR method for oriented TGS crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of strontium chloride on the optical and mechanical properties of γ–glycine crystals

Single crystals of γ‐glycine have been grown from aqueous solution in the presence of small amount of strontium chloride. Single crystal X‐Ray diffraction analysis was used to measure the unit cell parameters and to confirm the crystal structure. The grown crystals have also been subjected to powder X‐Ray diffraction study to identify the crystalline nature. The presence of all the functional groups of the γ‐glycine has been confirmed by Fourier Transform Infrared (FTIR) spectral analysis. The presence of hydrogen and carbon in the glycine molecules was confirmed by using proton and carbon nuclear magnetic resonance (NMR) spectral analyses. Optical behavior of the crystal was studied using UV – Visible absorbance spectroscopy and second harmonic generation (SHG) studies. The SHG efficiency of γ‐glycine is greater than that of standard potassium dihydrogen phosphate (KDP). Mechanical strength of the γ‐glycine crystal has been determined by microhardness studies. Thermal stability of the grown crystal is probed using thermo gravimetric analysis and differential thermal analysis. Laser damage threshold value has been determined using Q‐switched Nd:YAG laser operating at 1064 nm and with 13 ns pulse width in single shot mode. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mixed magnesium and nickel nitrate hexahydrates: an unexpected restructuring

Single crystals of the congruently melting equimolar mixture of magnesium nitrate hexahydrate and nickel nitrate hexahydrate have been grown. The compound crystallizes in a structure foreign to both components, namely in the monoclinic cobalt nitrate hexahydrate structure. The cations are located at random on the cation sub-lattice of the latter crystalline structure.     

Growth,dielectric and photoconducting studies of tetrathiourea mercury(II) tetrathiocyanato zinc(II) NLO single crystals

A highly efficient nonlinear optical single crystals of tetrathiourea mercury (II) tetrathiocyanato zinc(II), Hg(N₂H₄CS )₄Zn(SCN)₄, (TMTZ) were conveniently grown from mixture solvent of ethanol–water by slow evaporation technique. The grown crystals exhibited needle-shaped morphology. The cell parameters of TMTZ single crystals were determined by single-crystal X-ray diffraction. The grown crystals were subjected to optical characterization by FT-IR, FT-Raman and UV–Vis–NIR techniques. The dielectric study of TMTZ showed low dielectric loss in the high-frequency region. The photoconductivity studies confirm that the TMTZ crystal has negative photoconducting nature.     

Characteristics of nickel ammonium sulphate crystals precipitated from aqueous solution

The main factors affecting the characteristics of precipitated nickel ammonium sulphate hexahydrate crystals from aqueous solution have been investigated. Over the range 20–35 °C, the crystal median size increases with temperature, but decreases with supersaturation. The size distribution is relatively unaffected by temperature, but becomes narrower at high supersaturations. The yield of crystalline precipitate is greatly increased when non-stoichiometric ratios of reactants are employed due to the sharp decrease in the equilibrium solubility.     

Characterization of pure and urea-doped γ-glycine single crystals grown by solution method

Pure and urea-doped gamma-glycine (γ-glycine) single crystals were grown by solution method with slow evaporation technique. When urea was added as dopant, morphological alterations were noticed in γ-glycine crystals. Structural characterization of the grown crystals was carried out by single and powder X-ray diffraction (XRD) methods and it is observed that the samples crystallize in non-centrosymmetric space groups. UV-visible transmittance studies were performed to analyse optical transparency of pure and urea-doped γ-glycine crystals and found that the crystals were transparent in the entire visible-NIR region. Density and melting point of the grown crystals were measured. Second harmonic generation (SHG) for the grown crystals of this work was confirmed using Nd:YAG laser. Thermogravimetric and differential thermal analyses (TG/DTA) thermograms reveal that the materials have good thermal stability. From Microhardness studies, it is observed that urea-doped γ-glycine crystal is harder than pure (undoped) sample.     

A comparative study on pure,l-arginine and glycine doped ammonium dihydrogen orthophosphate single crystals grown by slow solvent evaporation and temperature-gradient method

Single crystals of pure, l-arginine and glycine doped ammonium dihydrogen orthophosphate (ADP) were grown by both the slow solvent evaporation method and the temperature-gradient method of Sankaranarayanan–Ramasamy (SR). The metastable zone width for different saturation temperatures of pure glycine and l-arginine added solutions were carried out. The grown crystals were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), optical transmission, dielectric constant, dielectric loss, and Vickers microhardness. The DSC and TG curves of the grown crystals indicated that they were stable up to 200 °C. The XRD study confirmed the structure of the grown crystal. The optical transmission analysis revealed that the pure and doped ADP crystals had very high percentage of transmission in the entire visible region. The important optical parameters such as reflectance and extinction coefficients of the grown crystals were calculated. l-arginine and glycine were used as dopants to reduce dielectric constant of ADP. The a.c. resistivity and a.c. conductivity were calculated. Dielectric loss of the doped ADP crystals grown by the SR method is lower than the doped ADP crystals grown by the conventional method. Larger hardness value for the SR method grown crystals confirmed greater crystalline perfection.     

Growth investigations of single crystal sulphates containing molecular glycine groups

Investigations on the optimalisation of the growth conditions of single crystals containing molecular glycine groups were performed and depending on the pH-value of the solution, crystals of triglycine sulphate, diglycine sulphate or diglycine sulphate monohydrate can be grown. The optimal pH-value for triglycine sulphate growing was found to be 1.5.     

Influence of doping on OH absorption in LiNbO3 crystals

Undoped, Cr doped and Mg, Cr codoped LiNbO₃ crystals were grown by conventional Czochralski technique. Comparative study was carried out using Fourier transform infrared (FTIR) and UV‐Visible spectroscopy. Infrared optical absorption for OH^– ion has been used to study the effect of dopants on the crystals. The peak position of OH^– shift to 3535 cm^‐1 for Mg, Cr codoped crystals compared to 3484 cm^‐1 for undoped and Cr doped crystals. Prominent absorption bands are found in the visible region centered at 480 nm (20833 cm^‐1) and 653 nm (15313 cm^‐1) in Cr doped crystals. Whereas in Mg, Cr codoped crystals these broad absorption bands are red shifted to 517 nm (19342 cm^‐1) and 678 nm (14749 cm^‐1). UV cutoff in Cr doped crystals shift towards higher wavelength compared to undoped LiNbO₃ crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural,thermal and optical characterizations of a NLO material: L‐alaninium oxalate

An organic electro‐optic and nonlinear optical (NLO) material, L‐alaninium oxalate, was synthesized by the standard method. The synthesized material was purified by repeated recrystallization. Single crystals were grown by the slow evaporation technique. The grown crystals were transparent and had optimum dimensions (20 × 3 × 2 mm³) and were characterized by single crystal XRD, FT‐NMR, FT‐IR, TGA‐DTA and UV‐Vis‐NIR techniques. The second harmonic generation (SHG) from the material was confirmed using Nd:YAG laser. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,growth and characterization of single crystals of pure and thiourea doped L‐glutamic acid hydrochloride

L(+)Glutamic acid hydrochloride [HOOC (CH₂)₂CH(NH₂) COOH·HCl], a monoamino dicarboxylic acid salt of L‐Glutamic acid was synthesized and the synthesis was confirmed by FTIR analysis. Solubility of the material in water was determined. Pure and Thiourea doped L‐Glutamic acid hydrochloride crystals were grown by low temperature solution growth using solvent evaporation technique. XRD, UV‐Vis‐NIR analyses were carried out for both pure and thiourea doped crystals. The crystals were qualitatively analyzed by EDAX analysis and the presence of thiourea was confirmed. The cell parameters of L‐Glutamic acid hydrochloride have been determined as a = 5.151 Å, b = 11.79 Å, c = 13.35 Å by X‐ray diffraction analysis and it crystallizes in orthorhombic space group P2₁2₁2₁. UV‐Vis‐NIR spectra analysis showed good optical transmission in the entire visible region for both pure and doped crystals. Micro hardness of both pure and doped crystals has been determined using Vickers micro hardness tester. The SHG efficiencies of both pure and doped crystals were determined using Kurtz powder test and pure L‐Glutamic acid hydrochloride crystal was found to possess better efficiency than thiourea doped L‐Glutamic acid hydrochloride crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of diaquatetrakis (thiocyanato) cobalt (II) mercury (II) N-methyl-2-pyrolidone (CMTWMP) single crystals

Single crystals of diaquatetrakis (thiocyanato) cobalt (II) mercury (II) N-methyl-2-pyrolidone, (CoHg(SCN)₄·(H₂O)₂·2(C₃H₆CONCH₃) (abbreviated as CMTWMP) were grown using slow solvent evaporation technique. The structure of the grown crystals was confirmed by single-crystal X-ray diffraction (XRD) technique. The optical properties of the crystals were investigated by Fourier transform infrared (FTIR) and UV–Vis–NIR transmission spectra. The grown crystals of CMTWMP were also subjected to dielectric, photoconductivity, thermal and microhardness studies. The photoconductivity study of CMTWMP confirms the electrochromism behaviour in the sample. The SHG efficiency of the sample was measured by Kurtz and Perry powder technique and its value is almost comparable with KDP.     

Growth and characterization of dichloro tetrakis thiourea nickel single crystals

Thiourea has a large dipole moment and has an ability to form extensive network of hydrogen bonds. In the course of our studies on new semiorganic NLO materials, thiourea is selected to combine with nickel chloride. Single crystals of tetrakis thiourea nickel chloride are grown using silica gel. Green transparent crystals of NTC (nickel thiourea chloride) of dimension 8x4x3 mm³ are grown in a period of 45 days. Single crystal XRD shows that the crystal belongs to body centered tetragonal symmetry class I4. The UV‐Vis‐NIR spectrum establishes the transmission range to be 300 nm to 2500 nm, with a sharp absorption peak at the red end of the visible region, which is due to the colour of the crystal. Photoconductivity and dielectric studies are also carried out. The mechanical strength of the crystal is estimated by Vickers hardness test. The crystal starts decomposing after about 200°C. Thus, we confirm from our present investigation that NTC is a suitable candidate for NLO applications. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth,optical and thermal studies of nonlinear optical L‐arginine perchlorate single crystals

A potentially useful semiorganic nonlinear optical (NLO) material, L‐arginine perchlorate, has been synthesized and bulk crystals have been grown by slow cooling technique. The grown crystals were characterized by single crystal X‐ray diffraction, UV‐Vis‐NIR spectroscopy, FT‐IR, thermal analysis and SHG measurements. The grown crystals were thermally stable upto 153°C and exhibit SHG efficiency of about 0.17 with respect of Urea. The etching studies have been carried out on the grown crystal. LAPC has good optical transmission not only in the visible range, however, also in the near UV part of the spectra and hence it is a potential material for nonlinear frequency conversion. The refractive index was measured by the Brewster's angle method. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,growth and characterization of l‐alaninium oxalate ‐ a novel organic NLO crystal

Nonlinear optical material of L‐alaninium oxalate (LAO) has been synthesized and single crystals are grown by slow evaporation technique. The solubility data of LAO is determined in water. Single crystal X‐ray diffraction study showed that LAO belongs to orthorhombic system with a non‐centrosymmetric space‐group P2₁2₁2₁. The functional groups have been identified from FT‐IR spectrum. The UV‐Vis‐NIR spectrum of LAO shows less optical absorption in the entire visible region. The second harmonic generation (SHG) in the material was estimated using Nd:YAG laser. The mechanical properties of the grown crystals are studied using Vickers microhardness tester. The AC and DC conductivity, and dielectric studies are also carried out and reported for the first time. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)