Rajneesh Mohan

HgO-added YBa2Cu3O7−δ superconductors

The HgO-added YBa2Cu3O7−δ (YBCO) superconductor has been studied for its structural and superconducting properties. Polycrystalline YBCO samples were synthesized through solid-state reaction method by adding HgO in different concentrations without using oxygen annealing. All the samples showed a sharp superconducting transition temperature around 90 K. The X-ray diffraction patterns of all the samples revealed monophasic Y-123 nature. The structural studies were carried out by neutron scattering and Rietveld analysis. The neutron scattering revealed that Hg is not incorporated in the Y-123 system and has shown optimum oxygen concentration. The significant role played by the HgO is to provide oxygen ambient through its decomposition, thus changing the oxygen balance in favour of high Cu-valence state.

Finite Element Analysis and Simulation of Al 7075 Alloy Joints Produced by Friction Stir Welding

The present work is mainly carried out to study the distribution of temperature in friction stir welded plate of Aluminium alloy. A 3-D finite element simulation model was developed to predict temperature distribution and residual stress in Friction Stir Welding (FSW) of Al 7075 alloy. The effect of angular velocity of tool, axial load and welding speed on the heat generated between the tool and plate to be welded was investigated. The simulations obtained were based on three factor five level central composite rotatable design. Second order polynomial equations for predicting the temperature was developed. Residual stresses for friction stir welded plates due to thermal cycles were predicted. The maximum temperature developed in friction stir welded plated increases with the increase of rotational speed of tool and axial load where as it decreases with increase in welding speed.

Study on thermal hysteresis of Sr doped manganites

We have studied the thermal hysteresis of dc electrical resistivity on the stoichiometric Nd0.67Sr0.33MnO3 and Pr0.67Sr0.33MnO3 manganites. The polycrystalline samples have been synthesized by solid state reaction method. The prepared samples were characterized by X-ray diffraction (XRD) for phase formation and low temperature dc resistivity measurement during both cooling and warming with standard four probe technique. The XRD patterns are indexed in orthorhombic unit cell (space group-Pnma). The resistivity data show a metal–insulator phase transition for both Pr0.67Sr0.33MnO3 and Nd0.67Sr0.33MnO3 samples with observable thermal hysteresis. Thermal coefficient of resistivity of all samples has also been studied.We have studied the thermal hysteresis of dc electrical resistivity on the stoichiometric Nd0.67Sr0.33MnO3 and Pr0.67Sr0.33MnO3 manganites. The polycrystalline samples have been synthesized by solid state reaction method. The prepared samples were characterized by X-ray diffraction (XRD) for phase formation and low temperature dc resistivity measurement during both cooling and warming with standard four probe technique. The XRD patterns are indexed in orthorhombic unit cell (space group-Pnma). The resistivity data show a metal–insulator phase transition for both Pr0.67Sr0.33MnO3 and Nd0.67Sr0.33MnO3 samples with observable thermal hysteresis. Thermal coefficient of resistivity of all samples has also been studied.

Effect of HgO Addition on the Resistivity Behaviour of La0.75Ca0.25MnO3

We have reported the effect of HgO addition on electrical resistivity of La0.75Ca0.25MnO3 manganites. The samples have been synthesised by conventional solid state reaction method. The pellets of these samples were sintered at 1200°u2009C in ambient atmosphere. These samples were characterized by X‐Ray diffraction technique and low temperature four probe resistivity measurement using closed cycle helium cryostat. From XRD analysis, these samples were found to have single phase orthorhombic (Pnma) crystal structure. From the resistivity vs temperature behaviour of these samples, it has been found that the resistivity of HgO added La0.75Ca0.25MnO3 decreases considerably in comparison to La0.75Ca0.25MnO3. It has also been observed that HgO addition decreases the metal—insulator transition from 242 K to 232 K which is due to cationic disorder created by HgO in La0.75Ca0.25MnO3.

Simple and Economical Method to Prepare Mg1−xMnxB2 Superconductor

The polycrystalline samples of Mg1−xMnxB2 (0⩽x⩽0.03) have been synthesized by using the solid state reaction method. The properties of the samples depend on the method of preparation. Generally, Tantalum foil is used for the preparation of MgB2 superconductor to reduce the formation of MgO phase. Here, we have reported a very simple and economical method for the preparation of Mg1−xMnxB2 (0⩽x⩽0.03) samples by using the stainless steel sheet instead of Ta foil. These results are well in agreement as prepared by using the Ta foil. All the samples were sintered at 850u2009°C for 2 hrs in the presence of high purity argon flow. The structural and eleclrical properties were studied by using the X‐Ray diffraction and four‐probe resistivity measurement techniques, respectively. The XRD patterns revealed the formation of MgB2 as the major phase. The superconducting transition temperature (Tc) decreases with increasing the Mn concentration. The Mn doping suppresses the transition temperature sharply as compared to the...