• V Hari Babu

      Articles written in Bulletin of Materials Science

    • Microhardness studies in ammonium halide crystals

      K J Pratap V Hari Babu

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      Microhardness studies of NH4Cl (pure and doped), NH4Br and alkali halide crystals are presented. The hardness of ammonium halides is found to be less as compared to alkali halide crystals. Doping NH4Cl crystals with copper (Cu2+) is found to increase the hardness enormously and the results obtained with various concentrations of copper are presented. The results have been analysed and the various factors contributing to the increase in hardness at lower loads have been discussed.

    • Galvanomagnetic properties of plastically deformed InSb single crystals

      M Nagabhooshanam V Hari Babu

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      The dc Hall effect, dc conductivity and mobility have been studied on deformed and undeformed samples ofn-type InSb from liquid nitrogen temperature to room temperature. These studies have shown that the Hall coefficient values of deformed samples do not differ much from undeformed sample, but a considerable amount of change was observed in mobility, suggesting that equal number of donor and acceptor type dislocations are introduced during the deformation process. In addition the mobility variation of the deformed samples with temperature has shown a peak in 170–300°K range. The dislocation mobility (μD) is deduced from the observed mobilities of deformed and undeformed samples. The plotμD vs T has two regions, region 1 being independent of temperature and region 2 having a linear increase with temperature. Theβ factor obtained from region 2 is found to be almost equal to the one calculated from Dexter and Seitz model. The dislocation densities at room temperature are also calculated for the deformed samples using the above model.

    • Influence of sintering time and quenching on the formation of highTc phase

      D Mangapathi Rao M Muralidhar T Somaiah V Hari Babu

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      Influence of sintering time and quenching in Bi2 −xPbxCa2Sr2Cu3Oy(x=0.0, 0.1, 0.2, 0.25, 0.3 and 0.4) samples have been studied by resistance and XRD measurements. In samples sintered at 850°C for 4 days,Tc(0) increases with Pb concentration.Tc(0) increased from 81 K forx=0.0 to 109 K inx=0.30 sample and then decreased. Increasing the sintering time to 10 days decreased theTc Quenching further decreased theTc(0). From X-ray diffraction patterns, the intensity peaks of low and highTc phases have been measured. The addition of Pb promotes highTc-phase. Sintering time, slow cooling and rapid quenching studies show that there is an optimum sintering time and cooling rate to produce a highTc-phase.

    • Role of lead in the growth of the highTc phase in the Bi2−xPbxSr2Ca2Cu3Oy systems

      L S Vaidhyanathan A M Niraimathi P Majumdar G Rangarajan M Muralidhar D Mangapathi Rao M Nagabhushanam V Hari Babu

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      Bi2−xPbxSr2Ca2Cu3Oy superconducting samples with 0<x<0·3 have been synthesized and characterized using X-ray powder diffraction.Tc and superconducting volume fraction have been measured using a.c. magnetic susceptibility, d.c. electrical resistivity as well as X-band microwave surface resistance in the normal state. The data indicate the growth of the highTc (2223) phase with corresponding reduction of the lowTc (2122) phase with increasingx, up to 0·25. Beyond this value ofx there is a slight deterioration of the superconducting behaviour.

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