• L C GUPTA

Articles written in Bulletin of Materials Science

• ESCA studies of some mixed-valence rare-earth intermetallics

ESCA (or XPS) studies of some rare-earth intermetallics were carried out using ESCA (3) Mark II and ‘ESCALAB’ machines from V G Scientific. The mixed valence nature of EuCu2Si2 and EuNi2P2 intermetallic compounds has been established. The 3d core-level photoemission spectra of Eu in EuCu2Si2 and EuNi2P2 exhibit two sets of structures corresponding to two different valence states of the rare-earth ions. Each of these sets shows simple spin-orbit splitting. The replicate splitting measured by us agrees well with those calculated by Herbst and Wilkins. The 3d core-level photoemission spectra of Eu is free from the multiplet splitting and satellite structure. The importance of 3d core-level photoemission studies in the understanding of valence fluctuation phenomenon has been emphasized.

• Role of oxygen content in the structural and the superconducting properties of high temperature superconducting ErBa2Cu3Oy

Samples of high temperature superconducting system ErBa2Cu3Oy prepared by the standard ceramic technique were found to have single phase. To vary the oxygen content in the samples, the mother compound was reduced by vacuum-annealing at different temperatures for a fixed period. The oxygen content was measured by gravimetric and iodometric titration procedures. The structural changes induced due to the variations in the oxygen content were studied by X-ray methods.

• Cooperative effect of Zn and Ga doping in YBa2Cu3O7

The creation of local magnetic moments at the plane and chain Cu-sites in YBa2Cu3O7 due to incorporation of Ga3+ and Zn2+ has been studied with respect to the superconducting transition temperature and structural parameters of the compound. The result indicates that the local moments are created due to slowing down of spin and charge fluctuations in the planes and chains respectively due to doping.

• Deposition of yttria-stabilized zirconia buffer layer on Si and its suitability for Y-Ba-Cu-O thin films

The deposition of yttria-stabilized zirconia (YSZ) as buffer layer on (100) silicon has been studied by rf sputtering with a view to subsequently preparing superconducting films of YBa2Cu3Ox on it. As-deposited films were found to be (100) oriented. The thermal mismatch and reaction between Si and YSZ at high temperatures were found to give rise to cracks in the films. Grain growth of buffer layer on annealing helped in the formation of superconducting phase.

• Superconducting Y-Ba-Cu-O films by rf sputtering in axial magnetic field

Films of Y-Ba-Cu-O system have been prepared by rf sputtering from composite Y-Ba-Cu-O targets in an axial magnetic field in 4:1 Ar/O2 mixture on 〈100〉 SrTiO3 and 〈100〉 MgO substrates at 270°C and 450°C. Although back-sputtering caused due to negatively-charged oxygen ions was found to drastically vary the film composition about the centre of the sputtering axis, by properly orienting the substrates with respect to the sputtering axis near-stoichiometric films have been obtained. Films annealed at 900°C in oxygen have shown superconducting onset at 88°K and zero resistance transition at 72°K.

• High-pressure studies of superconductivity in BiO$_{0.75}$F$_{0.25}$BiS$_2$

BiO$_{0.75}$F$_{0.25}$BiS$_2$ crystallizes in tetragonal CeOBiS$_2$ structure (S. G. P4/nmm). We have investigated the effect of pressure on magnetization measurements. Our studies suggest improved superconducting properties in polycrystalline samples of BiO$_{0.75}$F$_{0.25}$BiS$_2$. The Tc in our sample is 5.3 K, at ambient pressure, which is marginal but definite enhancementover $T_c$ reported earlier ($=$5.1 K). The upper critical field Hc2(0) is greater than 3 T, which is higher than earlier report onthis material. As determined from the M–H curve, both H$_{c2}$ and H$_{c1}$ decrease under external pressure $P$ ($0 \leq P \leq 1$ GPa). We observe a decrease in critical current density and transition temperature on applying pressure in BiO$_{0.75}$F$_{0.25}$BiS$_2$.

• # Bulletin of Materials Science

Volume 43, 2020
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Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019