R. B. Tripathi

Study of silver addition to Y1Ba2Cu3O7−y screen printed thick films

A study of the effect on the superconducting and microstructural properties of YBa2Cu3O7−x screen printed thick films as a function of silver content (in the form of Ag and Ag2O) from 0 to 40 wt. % by employing different experimental techniques has been carried out. It has been found that silver improves the sinterability and intergrain connectivity and reduces the normal state resistivity. The superconducting transition temperature of the above films was found to be in the range of 82 to 91 K. Our results show that a small addition of silver (Ag or Ag2O) helps in enhancing the superconducting properties. However, large amounts lead to formation of 211 phase as the decomposed product and thereby deteriorate the quality of the superconductor. Silver has been found to remain as metal in the samples for the entire range. Further, in light of our results, it seems that an addition of Ag metal is more beneficial than the addition of Ag2O.

Magnetotransport of La0.70Ca0.3−xSrxMnO3(Ag): A potential room temperature bolometer and magnetic sensor

Here we report the optimized magnetotransport properties of polycrystalline La0.70Ca0.3−xSrxMnO3 and their composites with Ag. The optimization was carried out by varying the Sr and Ag contents simultaneously to achieve large temperature coefficient of resistance (TCR) as well as low field magnetoresistance (MR) at room temperature. Sharpest paramagnetic (PM)-ferromagnetic (FM) and insulator-metal (IM) transition is observed in the vicinity of the room temperature (TC≈300 K≈TIM) for the composition La0.70Ca0.20Sr0.10MnO3:Ag0.20. Partial substitution of larger Sr2+ ions at the Ca2+ ions sites controls the magnitude of the FM and IM transition temperatures, while the Ag induces the desired sharpness in these transitions. For the optimized composition, maximum TCR and MR are tuned to room temperature (300 K) with the former being as high as 9% and the later being ∼20% and ∼30% at 5 and 10 kOe magnetic fields respectively. Such sharp single peak (TCR∼9%) at room temperature can be used for the bolometric and ...

Influence of V2O5 on the densification and the magnetic properties of Ni—Zn ferrite

Abstract The effects of V2O5 addition on the densification and the magnetic properties of the Ni—Zn ferrites have been studied. The maximum density was observed at a V2O5 content of 0.2 mo1% and 0.5 mo1% in iron excess and deficient ferrites respectively. The minimum loss factor occured at a V2O5 content of 0.4 mo1% irrespective of sintering temperature in both iron excess and iron deficient compositions. The variation of Curie temperature with the amount of V2O5 (⩽ 1 mo1%) added suggests that V2O5 goes into solid solution in the Ni—Zn ferrites, though the lattice parameter does not change appreciably with such addition.

Influence of sintering temperature and oxygen annealing on transport properties of La0.67Ca0.33MnO3

We investigate the influence of sintering temperature and annealing conditions on the transport properties of La0.67Ca0.33MnO3 (LCMO) samples prepared by the solid-state reaction method. In the plot of resistance as a function of temperature, R(T), we observe two peaks for air-annealed samples, which is attributed to the inhomogeneous distribution of oxygen—whereas the sample annealed in oxygen shows only a single peak, which is explained on the basis of homogeneous distribution of oxygen and grain connectivity. The sharpness in the transition peak is described in terms of the temperature coefficient of resistance, which is calculated using R(T) data. We present and compare here the results of structural, transport and magnetic measurements of LCMO prepared at different sintering temperatures as well as under different annealing conditions. The results of the compound are mainly discussed in terms of grain growth and the grain boundaries.

Transformation of 2212 to 2223 phase in the Bi-Sr-Ca-Cu-O system

Single phase Bi2Sr2Ca1Cu2O8 (2 2 1 2) superconductor with T°c around 85 K was transformed to nearly a single phase Bi2Sr2Ca2Cu3O10 (2223) having T°c around 115.5 K by reacting at 860°C with CaO and CuO (1 mol each of CaO and CuO, per formula composition Bi2Sr2Ca1Cu2O8) with addition of Pb for stabilization. A sample prepared under identical conditions but using the Bi2Sr2Ca2Cu3Oy nominal composition, however, showed only a very small amount of 2223 phase with T°c around 107 K. The corresponding changes in the superconducting phases and morphologies were also systematically investigated and found that uniform and sufficient supply of Ca and Cu ions in the correct proportions at early stages in the processing might have led to a key role during the subsequent 2212–2223 phase transformation.

Synthesis and characterization of Y-Ba-Cu-O and Bi(Pb)-Sr-Ca-Cu-O superconductors from the oxine co-precipitation method

Oxide superconductors in the Y-Ba-Cu-O and Bi(Pb)-Sr-Ca-Cu-O systems with Tc degrees of 93.6 K and 115 K, respectively, have been prepared by the co-precipitation process via the oxine route using nitrates as the starting materials. Chemical homogeneity, stoichiometry and fine particles of the precursor obtained by this process permit a relatively short time for the production of Y- and Bi-based superconducting compounds compared with that obtained by the conventional solid state reaction method. The resulting densities of the sintered samples were typically greater than 90%. X-ray diffraction analysis, energy dispersive spectral analysis and scanning electron microstructural analysis are also reported in this study.

Oxidation studies of Y-Ba-Cu superconducting oxides

Abstract The oxidation characteristics of quenched samples of Y-Ba-Cu-O system, using thermogravimetric analysis (TGA); differential thermal analysis (DTA) and X-ray diffraction analysis, has been reported. A weight gain of 3.75% has been recorded in thermogravimetry experiment. The observed 3.75% change in weight of the quenched sample during heating or cooling cycle may be attributed to the multiphase compound formation due to decomposition reaction in the sample at 950°C.

Pentavalent vanadium ion addition to Ni-Zn ferrites

Systematic studies of the changes in microstructure and the grain-growth kinetics of iron-deficient and iron-excess Ni-Zn ferrites with varying contents of V2O5 have been undertaken. The basic composition of an iron-deficient Ni-Zn ferrite showed a duplex structure. Modified microstructures with pore-free and uniform grains were obtained on V2O5 doping. A regular increase in grain size was found with increasing V2O5 content both in iron-deficient and iron-excess compositions. The square of the average grain diameter varied linearly with sintering time up to 0.0 to 0.4 mol % V2O5. For higher V2O5 contents (0.6 to 1.0 mol %), the cube of the average grain diameter was directly proportional to the sintering time. Modifications in the microstructure and the grain growth have been explained in terms of the solubility of V2O5 in the lattice and liquid-phase formation at the grain boundaries.

The influence of second phase precipitation on SiO 2 /GeO 2 doped Ni-Zn Ferrite properties

SiO 2 and GeO 2 have been found to have limited solubility in the Ni-Zn ferrite. SiO 2 having negligible solubility is seen to segregate as a dispersed phase, which reduces grain boundary mobility during sintering. Unreacted GeO 2 (m.p. ≃ 1100°C), on the other hand, forms a free flowing liquid phase, which wets the grain and promotes faster grain growth during sintering. The initial permeability decreases significantly with increasing GeO 2 additions. The bulk conductivity σ dc of the samples containing higher concentrations of these dopants shows an anamolous temperature dependence which is typical to the Schottky thermoionic emission. Such phenomena are discussed in terms of the second phase precipitation. The domain wall energy γ is also seen to increase significantly at higher dopant concentrations reflecting an increase in the internal stresses, caused primarily by these precipitates.

The effect of thermal cycling on two-step enhanced superconducting transition in Bi1.6Pb0.4Sr2Ca1Cu2O8+x

Abstract A superconducting drop around 120 K with zero resistance temperature around 101K has been obtained in Bi 1.6 Pb 0.4 Sr 2 Ca 1 Cu 2 O 8+ x samples. Study of effect of thermal cycling on the superconducting properties has suggested that both the above enhanced transitions belong to the low- T c Bi-2212 phase.