Growth of triglycine sulfate crystals doped with alkali and transition metal ions and study of their different physical and optical properties

Abstract

Growth of single crystals is an area of technological advancement and scientific research which has blossomed into a full-fledged area in the field of science, engineering and technology. Modern technology is based on the single crystals of nonlinear optical, semiconductor, dielectric, ferroelectric, piezoelectric, infrared sensitive materials, acoustio-optic and optoelectronic materials. Large size single crystals are essential for device fabrication and efforts are always taken to grow large crystals. Triglycine sulphate (TGS) crystal has given much interest among scientists and researchers for many years. With an aim of discovering new useful materials for both academic and industrial uses, we have attempted to grow pure TGS and also to modify TGS by means of doping it separately with transition metal like Nickel Sulfate (NiSO4) and alkali metal, Lithium Sulfate (LiSO4) and Potassium Bromide (KBr) with five different concentrations (0.1, 0.3, 0.5, 0.7 and 1 mole %) in each case. Pure TGS and doped TGS single crystals with considerable dimensions were successfully grown by the natural evaporation method from aqueous solutions. The mass growth rate of all the grown crystals was investigated. In the case of LiSO4 and KBr doped TGS crystals, growth rate increases with dopant concentrations (0.1 mole % to 1 mole %) but the growth rate of NiSO4 Energy Dispersive X-ray (EDX) analysis confirms the presence of elements (C, N, O and S) into the pure TGS and the presence of Ni doped TGS crystals decreases with dopant concentration (0.1 mole % to 1 mole %). All the grown crystals are well faced, optically transparent, defect free, colourless and good quality single crystals. Solubility increases with temperature (30º-50 ºC) and also increases with dopant concentrations (0.1 to 1 mole %) and thereby possess positive solubility coefficient. +2 and K+2 in the NiSO4 doped and KBr doped TGS crystals. The Fourier Transform Infrared (FTIR) spectra of all grown crystals have been recorded in the wavenumber range of 400-4000 cm-1 by KBr pellet technique and the associated functional groups of the grown crystals. The structural studies on the grown crystals were carried out by X-ray diffraction analysis and has found that all the grown crystals crystallize in monoclinic structure. The lattice cell parameters of pure TGS are a = 9.6010 Å, b = 12.5600 Å and c = 5.4500 Å. There are slight variations in the lattice parameters and cellvolume of the doped crystals. These variations are due to the incorporation of dopants (Ni+2, Li+2 and K+1 The optical transmission spectral analysis of the grown crystals was carried out between 190 to 1100 nm. Pure TGS crystal has a transmission of more than 84.26% in the visible region. NiSO ion) into the crystal lattice. 4 and KBr doped TGS crystals have lower percentage transmission in compared to that of undoped TGS crystal and the transmission is decreased with the increase in molar concentration (0.3, 0.5 and 1 mole %) of NiSO4 and KBr. But LiSO4 doped TGS crystals have higher percentage of transmission compared to that of undoped TGS crystals and the transmission increased with the increase in molar concentration (0.1 to 1 mole %) of LiSO4 The grown crystals were thermally characterized by Thermo Gravimetric and Differential Thermal Analysis (TG/DTA). The grown crystals are thermally stable up to about 230 ºC. They are mechanically characterized by making the microhardness measurements. The microhardness numbers of doped (LiSO. 4, NiSO4 and KBr) TGS crystals are found more than pure TGS crystal. The microhardness number increases (70-113 kg/mm2 DC electrical conductivities were measured by using the two probe method along the b-direction at various temperatures. The DC conductivity increases (0.2 x 10) with dopant concentrations (0.1 to 1 mole %). -6 – 7.8 x 10-6 Dielectric constant, dielectric loss tangent and AC electrical conductivities were determined for all grown crystals with a fixed frequency of 1 kHz at various temperatures along the b-direction. Curie temperature remains same (49 °C) for pure and doped (LiSOmho/m) with the increase in temperature (40 °C- 100 °C) and dopant concentration (0.1 mole % to 1 mole %). 4, NiSO4 and KBr) TGS crystals but dielectric constant, dielectric loss and AC conductivity increases (0.1 x 10-7 – 7.9 x 10-7 mho/m) with dopant concentrations (0.1 to 1 mole %). Surface morphology was analyzed by etching study. For LiSO4 doped TGS crystals, dislocation density decreases with dopant concentrations (0.1 mole % to 1 mol %). For NiSO4 and KBr doped TGS crystals, dislocation density increases with dopant concentrations (0.1 mole % to 1 mole %). So it can be stated that LiSO4 doped TGS crystal is more crystalline than pure, NiSO4 From technological application point of view, it may be stated that these as grown defect free, good quality, optically transparent, thermally and mechanically stable crystals may be suitable materials for use in optoelectronic devices. The low dielectric constant at room temperature and high mechanical hardness suggest that the doped TGS crystals could be good candidate for infrared detectors.