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Author: search.filters.author.Mahendra, K.Subject: search.filters.subject.Single crystals

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    Synthesis, structural, optical and electrical (DC) properties of a semiorganic Thiourea Barium Chloride (TBC) single crystal
    (Elsevier GmbH journals@elsevier.com, 2017) Mahendra, K.; D'Souza, A.; Udayashankar, N.K.
    In the present study, TBC single crystals were synthesized using solution evaporation method. The structural analysis of TBC crystal was studied using Powder X-ray diffraction. Optical properties of TBC crystals were carried out using UV–vis, FTIR, Raman and photoluminescence (PL) spectra. The crystal shows absorbance maxima at 209 nm and transparent in the visible region 300–900 nm. The various optical constants such as refractive index, reflectance, speed of light, extinction coefficient, electrical susceptibility, dielectric constant, optical and electrical conductivity were evaluated. Thus results revealed that all these optical constants shows a strong dependence on optical absorption coefficient. Using single oscillator model (Wemple ?Didomenico), lattice dielectric constant and the ratio of free charge carrier to their effective mass were evaluated. The PL study of TBC crystals shows two emission peaks (419 nm ?S, 441 nm- Ba) in blue region. The DC resistivity and conductivity of the crystal was investigated in the temperature range 26 °C–115 °C. © 2017 Elsevier GmbH
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    Effect of Zn doping on the structural, optical, photoluminescence and mechanical properties of thiourea barium chloride (TBC) crystal
    (Elsevier Ltd, 2017) Mahendra, K.; D'Souza, A.; Udayashankar, N.K.
    In the present work, a synthesis and comparative study on the effect of Zinc (Zn) on thiourea barium chloride (TBC) single crystals has been reported. Crystals of thiourea barium chloride and Zn-doped thiourea barium chloride crystals are prepared using slow evaporation from the saturated solution. The samples were subjected to single crystal and powder X-ray diffraction to study the unitcell parameters and structural variations. The functional groups present in the crystals are derived using FTIR and Raman analysis. The enhancement of transmittance with the addition of Zn and the variations in the parameters such as bandgap, extinction coefficient, reflectance, refractive index, optical and electrical conductivity, real and imaginary part of dielectric constant are studied from UV–vis spectrum analysis. Vickers hardness measurements are conducted for pure and Zinc-doped TBC single crystals. The emission spectrum of pure and Zn doped single crystals are studied using photoluminescence analysis. © 2017 Elsevier Ltd
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    Gamma irradiation effect on structural, optical and electrical properties of organometallic potassium hydrogen oxalate oxalic acid dihydrate single crystal
    (Springer New York LLC barbara.b.bertram@gsk.com, 2018) Mahendra, K.; Nayak, K.K.; Fernandes, B.J.; Udayashankar, N.K.
    Potassium oxalate oxalic acid dihydrate (KHO) single crystals were grown from solvent evaporation technique at room temperature. Crystals were optically characterized using UV–Vis and photoluminescence analysis. The gamma irradiation effects on KHO crystals were also studied optically and the results were analyzed to compare the effect of irradiation on the crystal lattice for different dosage. Structural variations were studied using powder XRD, FTIR and the results were examined to study the defect states created inside the lattice due to irradiation and the effect on the functional vibrations of the host crystal. Surface morphology of the crystal was studied using scanning electron microscope (SEM). Photo conductivity of the synthesized crystals were studied and analyzed to compare the photo response as well as the conductivity of the materials when subjected to irradiation. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.
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    Enhanced structural, optical, thermal, mechanical and electrical properties by a noval approach (nanoparticle doping) on ferroelectric triglycine sulphate single crystal
    (Springer Verlag service@springer.de, 2019) Mahendra, K.; Kumar, H.K.T.; Udayashankar, N.K.
    The pristine and AgNP-doped TGS crystals are studied using powder X-ray diffraction, density measurements, solubility studies, UV–Vis analysis, photoluminescence spectroscopic analysis, thermal gravimetric analysis, differential thermal analysis, differential scanning calorimetry, Vicker’s hardness measurements, I–V and impedance measurements. From the XRD studies, TGS crystal formation is confirmed and by further analyzing X-ray diffraction data it is noticed that the incorporation of nanoparticles induce stress in the lattice of TGS crystal, which, in turn, lead to shift in peak positions. Crystal solubility and density values are increased after doping process. From the emission spectrum it is evident that emission intensity increases as the doping concentration increased. The melting point and mechanical hardness of the crystals also showed improvement after AgNP doping. Band gap calculated by Tauc’s relation is found to decrease with increase in doping concentration. Further, electrical studies demonstrated that crystal conductivity is improved as the doping concentration increases. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.
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    Modulations of physio-chemical and electronic properties of metalorganic KHO single crystals through Co(OH)2 nanoparticles doping
    (Springer New York LLC barbara.b.bertram@gsk.com, 2019) Mahendra, K.; Bhat, K.S.; Nagaraja, H.S.; Udayashankar, N.K.
    Semiorganic crystals play vital role in the design and development of optical devices. In this context, we report the synthesis of metalorganic potassium hydrogen oxalate oxalic acid dihydrate (KHO) single crystals using slow solvent evaporation technique. Further, Co(OH)2 nanoparticles pre-synthesized using hydrothermal method are doped to KHO single crystals. Doping of Co(OH)2 nanoparticles in the crystal system were confirmed through XRD, EDAX and PL measurements. The XRD measurements indicate a shift in the peak positions and variation in the overall intensities. On the other hand, PL measurements also indicate enhanced emission peaks confirming the successful doping of Co(OH)2 nanoparticles in the KHO system. As the effect of doping, the declination in the optical bandgap and improvement of electronic conductivity were also observed. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.
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    Growth and comparative studies on oxalic acid dihydrate, potassium oxalate hydrate and potassium hydrogen oxalate oxalic acid dihydrate single crystals
    (Elsevier Ltd, 2020) Mahendra, K.; Udayashankar, N.K.
    Single crystals of Oxalic acid dihydrate (OAD), Potassium oxalate hydrate (KOH), Potassium hydrogen oxalate oxalic acid dihydrate (KHOOD) were grown using solvent evaporation technique. Unit cell parameters of the crystals were studied using single crystal XRD (SCXRD) and the crystal parameters were found to match with the reported values. Structural properties were studied using powder XRD analysis. Optical absorption studies were carried out to determine the light absorption by the crystal and the optical bandgap was also calculated using Tauc's relation. Emission and thermal properties of the OAD, KOH and KHOOD crystals were studied using photoluminescence spectroscopy (PL) and TGA-DTA measurements respectively and explained in detail. Electrical studies were also carried out to find the resistivity of the material. The hardness of the synthesized crystal was also explored and the parameters such as stiffness constant, yield strength, fracture toughness and brittleness were evaluated and compared. © 2019 Elsevier Ltd
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    Investigation on mechanical and temperature dependent electrical properties of potassium hydrogen oxalate oxalic acid dihydrate single crystal
    (Elsevier B.V., 2020) Mahendra, K.; Udayashankar, N.K.
    The potassium hydrogen oxalate oxalic acid dihydrate (KHOOD) single crystals were grown using solvent evaporation technique. The mechanical hardness of grown KHOOD single crystal was performed using Vickers microhardness tester and investigated for different loads starting from 10 g to 100 g and it was decided to include under hard material category. The mechanical parameters such as elastic stiffness and yield strength were calculated and discussed in detail. Temperature dependent I-V, dielectric studies were performed and explained in detail. © 2020 Elsevier B.V.
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    Effect of methyl orange dye molecule on the structural, optical and electrical properties of the KHOOD single crystals
    (Springer, 2020) Mahendra, K.; Pujar, S.; Udayashankar, N.K.
    In the present investigation, synthesis of pristine and methyl orange dye-doped potassium hydrogen oxalate oxalic acid dihydrate (KHOOD) single crystals are reported. In this study, the structural properties of the crystals were investigated using powder XRD and the effect of dye incorporation on the KHOOD crystal was explored in detail. The effect of dye molecule on the optical absorption of the crystal was studied and the optical band gap was calculated using Tauc relation and presented in detail. Further, the effect on emission and mechanical properties of the crystals were also explored after doping with the dye molecule. Furthermore, the crystals were also studied electrically by subjecting to varying electrical frequencies (A.C) and the properties of pristine and doped crystals were compared and explained in detail. The modulus properties of the crystals were studied and compared. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
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    Effect of Erioglaucine dye dopant on the structural, optical, mechanical, electrical and nonlinear properties of ammonium dihydrogen phosphate single crystal
    (Elsevier B.V., 2020) Fernandes, J.M.; Mahendra, K.; Udayashankar, N.K.
    The structural, optical, mechanical, electrical and nonlinear properties of standard Ammonium Dihydrogen Phosphate (NH4H2PO4, ADP) single crystals incorporating organic Erioglaucine dye dopant are presented. The effect of Erioglaucine dye dopant at varied concentration on these properties has been investigated through measurement of powder X-Ray Diffraction (XRD), UV–Vis and photoluminescence spectroscopy, Vickers microhardness, light dependent I–V measurements and Second Harmonic Generation studies. These measurements reveal that doping with increasing dye concentration of Erioglaucine leads to change in properties of the ADP single crystals, making them suitable for optoelectronic applications. The Erioglaucine doped ADP single crystals were grown using solvent evaporation technique at room temperature. Optical properties like absorbance and emission of these crystals are determined using UV–vis and photoluminescence spectroscopy, respectively. Optical bandgap and photoluminescence of the crystals are found to increase with dye doping, indicating their suitability in photonic applications. The mechanical properties of the crystals are determined using Vickers microhardness measurement technique. Light dependent I–V measurements exhibit negative photoconductivity behavior of the ADP crystals. However, the current through the crystals is observed to increase with increase in doping concentration of the Erioglaucine dye. Second Harmonic Generation studies show enhancement in nonlinearity for doped crystals. Our experiments indicate gradual variance in the crystallinity, emission, hardness, conductivity and nonlinearity of the sample with change in dye concentration. © 2020 Elsevier B.V.
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    A novel approach to the synthesis of semiorganic ammonium hydrogen oxalate oxalic acid dihydrate single crystal and its characterization
    (Springer Science and Business Media B.V., 2021) Mahendra, K.; Fernandes, J.M.; Udayashankar, N.K.
    A different approach used in the synthesis of ammonium hydrogen oxalate oxalic acid dihydrate (NH4H3(C4O8)·2H2O) single crystals is presented. The crystals are synthesized using solvent evaporation technique. The analysis of the synthesized NH4H3(C4O8)·2H2O single crystals has been carried out through measurements such as single-crystal X-ray diffraction (SCXRD), powder XRD, UV–Vis and photoluminescence spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric and differential thermal analysis (TG–DTA), Vickers microhardness measurements and current versus voltage (I–V) characteristics. The evaluation of the molecular structure of the crystals using SCXRD shows that they belong to the triclinic crystal system with space group P-1. The structural properties of the crystals are also evaluated using powder XRD measurements on their finely crushed powder. These measurements corroborate the results of SCXRD and confirm the triclinic system of the crystals. The optical properties like absorbance and emission of these crystals are determined using UV–Vis and photoluminescence spectroscopy, respectively. These measurements show that the crystals exhibit substantial emission in the blue region. The thermal stability and the decomposition mechanism of the crystals is studied using TG–DTA analysis. The mechanical strength of the crystals is determined using Vickers microhardness technique. The photoresponse of the NH4H3(C4O8)·2H2O crystals is analyzed from light-dependent I–V characteristics, and it is observed that the crystals exhibit photoresistive behavior. © 2020, Akadémiai Kiadó, Budapest, Hungary.