Budhendra Singh

Enhanced Thermal Conductivity and Viscosity of Nanodiamond-Nickel Nanocomposite Nanofluids

We report a new type of magnetic nanofluids, which is based on a hybrid composite of nanodiamond and nickel (ND-Ni) nanoparticles. We prepared the nanoparticles by an in-situ method involving the dispersion of caboxylated nanodiamond (c-ND) nanoparticles in ethylene glycol (EG) followed by mixing of nickel chloride and, at the reaction temperature of 140°C, the use of sodium borohydrate as the reducing agent to form the ND-Ni nanoparticles. We performed their detailed surface and magnetic characterization by X-ray diffraction, micro-Raman, high-resolution transmission electron microscopy, and vibrating sample magnetometer. We prepared stable magnetic nanofluids by dispersing ND-Ni nanoparticles in a mixture of water and EG; we conducted measurements to determine the thermal conductivity and viscosity of the nanofluid with different nanoparticles loadings. The nanofluid for a 3.03% wt. of ND-Ni nanoparticles dispersed in water and EG exhibits a maximum thermal conductivity enhancement of 21% and 13%, respectively. For the same particle loading of 3.03% wt., the viscosity enhancement is 2-fold and 1.5-fold for water and EG nanofluids. This particular magnetic nanofluid, beyond its obvious usage in heat transfer equipment, may find potential applications in such diverse fields as optics and magnetic resonance imaging.

Key aspects of L-threoninium picrate single crystal: an excellent organic nonlinear optical material with a high laser-induced damage threshold

Recent trends focuses on the usage of nonlinear optical materials owing to their increasing demand in frontier areas of optical communication and switching applications. In the present work single crystal of L-threoninium picrate, an excellent material for nonlinear optical applications was grown using conventional slow evaporation solution technique to meet the increasing demand of photonics industry. The lattice parameters of the grown crystal were analysed by using powder X-ray diffraction, and it was found that it crystallised in monoclinic system with space group P21. The strain in the lattice of the grown crystal was calculated using Hall–Williamson relation. Crystalline perfection of the grown crystal was assessed using high resolution X-ray diffraction technique and observed that quality of crystal was fairly good. Optical transmission analysis and band gap evaluation were performed using UV-Vis spectroscopy. Laser damage threshold value for the crystal was also measured and was found to be higher than most of reported organic single crystals. Optical homogeneity of the crystal and birefringence was evaluated using modified channel spectrum method. Thermal behaviour of the grown specimen was examined by using photopyroelectric technique. Further its various mechanical properties, such as hardness, stiffness, youngs modulus, were measured using nanoindentation technique.

Ferroelectricity in glycine picrate: An astonishing observation in a centrosymmetric crystal

Remarkable ferroelectric property has been observed in the glycine picrate single crystal though it crystallizes in centrosymmetric structure. An anomaly at 105 °C was observed in dielectric and ac conductivity measurements. The activation energies for conduction (Ea) below and above this temperature are found to be 0.31 and 0.53 eV, respectively. The remanant polarization (Pr) and coercive field (Ec) at room temperature were found to be 0.64 μC/cm2 and 6.22 kV/cm, respectively. However, a remarkable increase in these values was observed above 105 °C. A significantly high d33 (piezoelectric charge coefficient) in the order of 18 pC/N was observed.

Growth, structural and mechanical analysis of a single crystal of L-prolinium tartrate: a promising material for nonlinear optical applications

A single crystal of L-prolinium tartrate (LPT), which is an organic non linear optical material, was successfully synthesized and grown using a slow evaporation solution growth technique (SEST). The crystal structure and lattice parameters of the crystal were confirmed by powder X-ray diffraction and it was found that it belongs to the monoclinic crystal system with β = 100.380 and a noncentrosymmetric space group. The presence of strain in the grown ingot was calculated from powder X-ray diffraction measurements. The crystalline perfection was examined by high resolution X-ray diffractometry, which revealed that the crystal contained structural grain boundaries. The optical behavior of the grown specimen was analyzed by photoluminescence (PL) spectroscopy and its time resolved PL decay was calculated. The grown crystal adopted a step wise growth pattern with parallel striations, which was confirmed from the etching technique. Its ferroelectric and piezoelectric properties were also assessed. Its third order non linearity was assessed using an open aperture Z-scan technique. The thermal parameters of the LPT single crystal were calculated using a photopyroelectric technique. The mechanical strength of the single crystal at the micro level was observed by nanoindentation using the Oliver–Pharr method.

Nucleation kinetics, growth, mechanical, thermal and optical characterization of sulphamic acid single crystal

Sulphamic acid (HSO3NH2) is a potential material that exhibits excellent piezoelectric and non-linear optical properties. Nucleation and growth kinetics give valuable information about the crystal growth process, which can be employed in the growth of large size crystals. Thus we have studied its nucleation parameters such as solubility, metastable zone width, induction period, interfacial tension, critical free energy, volume free energy change, critical nucleus and found that good quality sulphamic acid crystal can be grown at low temperature. Growth of good quality crystal was done by adopting slow evaporation solution growth technique at room temperature and as a result, good quality single crystal was grown. The grown bulk single crystal of the title compound was subjected to various characterization analyses. Its unit cell dimensions were confirmed using powder X-ray diffraction. Further its crystalline perfection was assessed using high resolution X-ray diffraction and X-ray topography techniques and it was found that it is reasonably good. Its various functional groups were identified from the Fourier transform-Raman method. Nanoindentation was performed to identify the load dependence and independence of hardness (H) and Youngs modulus (E) using the Oliver–Pharr method and it was found that both H and E exhibit peak load dependence. Photopyroelectric study was performed to identify its thermal properties such as thermal diffusivity (α), thermal conductivity (k), thermal effusivity (e), and heat capacity (cp). These studies reveal that it has high thermal stability compared to other single crystals. The optical homogeneity of the grown crystal was assessed using a birefringence interferometer and it was found to be reasonably good.

Flux growth of 0.94[Na0.5K0.5NbO3]–0.06LiNbO3 piezo-/ferroelectric crystals for long duration and high temperature applications

High quality lead free ferroelectric single crystals of 0.94[Na0.5K0.5NbO3]–0.06LiNbO3 (NKLN) were grown by the self-flux method. The crystals were characterized for structural and dielectric properties, piezo/ferro response (both on the macro and microlevel) and electrical behavior. The characterization confirmed a perfectly homogeneous stoichiometry having negligible defects in the sample. Further, the crystals were found to exhibit high Curie phase transition (~420 °C) with a high value of d33 coefficient (=115 pC N−1) and remnant polarization (=4.01 μC cm−2 at 30 °C). Its pyroelectric coefficient was found to be ~309.8 μC m−2 °C−1. In addition, the crystals did not show any fatigue. Further, ferroelectric domains were analyzed using piezoresponse force microscopy and the effective d33 coefficient on the microlevel was calculated to be ~80 pm V−1 after a 20 min relaxation of 75 V induced bias. The results suggest NKLN crystals to be a very promising material in the family of available lead free materials for various ferroelectric applications.

Growth, crystal structure, Hirshfeld surface, optical, piezoelectric, dielectric and mechanical properties of bis­(l-asparaginium hydrogensquarate) single crystal

Molecular organic single crystals of bis(L-asparaginium hydrogensquarate) monohydrate [BASQ; (C8H10N2O7)2·H2O] have been grown by solution technique. Crystallographic information was investigated by single-crystal X-ray diffraction (SCXRD) analysis. Hirshfeld surface and fingerprint plot studies were performed to understand the intermolecular interactions of the BASQ crystal in graphical representation. Functional group identification was studied with FT-IR (Fourier transform-IR) spectroscopy. The positions of proton and carbon atoms in the BASQ compound were analyzed using NMR spectroscopy. High transparency and a wide band gap of 3.49 eV were observed in the linear optical study by UV-vis-NIR spectroscopy. Intense and broad photoluminescence emissions at room temperature were observed in blue and blue-green regions. The frontier molecular orbitals of the BASQ molecule were obtained by the DFT/B3LYP method employing 6-311G** as the basis set. The dielectric study was carried out with temperature at various frequency ranges. The piezoelectric charge coefficient (d33) value of BASQ crystal was found to be 2 pC/N, which leads to its application in energy harvesting, mechanical sensors and actuators applications. In the non-linear optical study, the BASQ crystal showed promising SHG conversion efficiency. Mechanical properties of the BASQ crystal were studied experimentally by Vickers microhardness technique, which revealed that the grown crystal belonged to the softer category. BASQ crystal void estimation reveals the mechanical strength and porosity of the material.

Successful aqueous processing of a lead free 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 piezoelectric material composition

We report on the successful aqueous processing of a lead free piezoelectric 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BZT–BCT) composition with the final functional properties of the materials unaffected by the various processing steps involved. X-ray diffraction results show a single tetragonal perovskite crystalline phase for the as-received sintered BZT–BCT powder. The purity of the perovskite phase for BZT–BCT powder was found to be controlled even after ageing the material in water for 24 h as a successful surface treatment against hydrolysis. An aqueous suspension of surface treated BZT–BCT powder with 50 vol% solid loading was successfully transformed into micro-sized granules via a freeze granulation (FG) method. Various structural, electrical and mechanical properties of sintered BZT–BCT-FG and BZT–BCT-NG ceramics consolidated from freeze granulated and non-granulated (NG) powders, respectively, were measured. The dielectric constant (er) values of the BZT–BCT-FG sample were found to be higher, with lower dielectric loss (tan δ) values in comparison with those of a sample prepared from the BZT–BCT-NG powder at all temperatures and with all frequency ranges tested. Nanoindentation results revealed that the ability to oppose deformation was nearly 10-fold higher for BZT–BCT-FG (6.93 GPa) than for BZT–BCT-NG ceramics (543 MPa). The functional properties of BZT–BCT-FG samples confirmed the benefits of the aqueous processing approach in comparison with traditional dry pressing.

Enhancement of thermoelectric figure of merit in Bi2Se3 crystals through a necking process

The growth of good quality bulk single crystals of bismuth selenide by employing a high-temperature vertical Bridgman technique with a specially designed ampoule having a provision for a necking process is reported. Several growth experiments were performed and reproducible results were obtained. The crystal structure and lattice dimensions were confirmed by powder X-ray diffraction (PXRD), the bulk crystalline perfection was assessed using high-resolution X-ray diffractometry and the good bulk crystalline perfection with an indication of layered structure was confirmed. Transmission electron microscopy (TEM) was carried out for the grown single crystal and confirmed the layered structure. High-resolution TEM (HRTEM) was also used to further assess the crystalline perfection. The direct measurement of d spacing obtained from HRTEM imaging was found to be in good agreement with the data obtained from PXRD. The thermal behavior was examined by differential scanning calorimetry and a sharp melting was found at 983 K, which revealed the purity of the bismuth selenide. The Seebeck coefficient and electrical and thermal conductivities were measured, and a thermoelectric figure of merit was calculated in order to assess the suitability of the crystal for thermoelectric applications such as refrigeration and portable power generation. Nanoindentation analysis was also performed for the first time.

Multiwalled Carbon Nanotubes Reinforced Portland Cement Composites for Smoke Detection

Smoke detection with multiwalled carbon nanotubes (MWCNTs)/cement composites have been studied. Pellets of MWCNTs reinforced Portland cement have been casted with varying MWCNTs %. The DC transient studies depicted an increase in conductivity when exposed to smoke. Responsivity in the range 26-46% has been obtained under smoky environment based on MWCNTs % in the composites. Ionic conductivity increased with frequency at room temperature under ambient and smoky environments. In this paper, we also report fabrication technique of the pellets and the sensing mechanism is explained on the basis of ionic conductivity of the cementitious material in combination with the conductive carbon fibers present in the porous matrix of the cement.