• S K Malik

      Articles written in Bulletin of Materials Science

    • Structural and magnetic investigations of some new boron containing rare earth intermetallic compounds

      S K Malik S K Dhar R Vijayaraghavan

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      By alloying boron with RPd3 (R=rare earth) compounds, new ternary alloys of the formula RPd3Bx (0 ≤x ≤ 1) have been prepared. The parent RPd3 compounds crystallise in the cubic AuCu3 type structure. The addition of boron does not change the structure but results in an expansion of the lattice. Therefore, it is likely that the small boron atoms occupy the vacant body centred position in AuCu3 type structure. It is also observed that compounds of the composition RRh3B can be formed in the cubic structure for all rare earths R though the parent RRh3 compounds exist only for R=Ce (AuCu3 type) and La, Sm, Nd and Gd (all hexagonal CeNi3 type). This points out the role of boron in stabilising new crystallographic phases. The results of susceptibility measurements on some of the RPd3B and RRh3B compounds are presented. In particular, it is noted that while GdPd3 orders antiferromagnetically withTN=6 K, GdPd3B does not order magnetically down to 4.2 K.

    • Magnetic properties of RRh3B2(R=La, Ce, Nd, Gd) compounds

      D Rambabu S K Dhar S K Malik R Vijayaraghavan

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      The11Bnmr results on RRh3B2(R=La, Ce, Nd and Gd) are reported. For CeRh3B2, specific heat and electrical resistivity are reported. From a comparative study of the11Bnmr Knight shifts and the spin lattice relaxation times of these compounds it is shown that in CeRh3B2, there is strong hybridization of 4f states with the conduction electrons. A local moment on Ce with admixture of 4f and 5d–6s orbitals is suggested.

    • Effect of heat treatment and composition on the superconductivity in Pb-Sr-R-Ca-Cu-O oxide system

      N C Soni Ram Prasad Kalyan Adhikary A Gulnar C V Tomy S K Malik

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      The effect of compositions, sintering temperatures and furnace atmospheres on the superconducting transition temperatures of several members of the series Pb2Sr2R1−xCaxCu3Oz(0.0⩽x⩽0.7, R=Y, Gd) has been studied. The effect of partial replacement of Pb, Ca and Y by In has also been studied. The shapes of the resistivity-temperature curves and the zero resistance temperatures are found to be extremely sensitive to the synthesis parameters employed. Superconductivity is not observed in samples treated in oxidizing atmosphere or heated at very high temperatures. Samples sintered in flowing nitrogen showed incomplete transition in resistivity starting at about 75 K and extending down to 15 K. A new and comparatively simple synthesis procedure involving treatment of the samples in vacuum has been employed to obtain nearly single-phase materials showing metallic behaviour. Using this procedure, samples of the above composition, but containing no Ca(i.e. Pb2Sr2RCu3Oz, R=Y and Dy), are also found to be superconducting with zero resistance up to 48 K.

    • Superconductivity studies on Tl-Th-Sr-Ca-Cu-O system

      K A Thomas U V Varadaraju G V Subba Rao C V Tomy S K Malik

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      Superconductivity with a maximumTc, zero of 58 K forx > 0·75 has been observed in a nominal starting composition, ThxTl2Sr2Ca2Cu3Oy. X-ray data show that the 1212 phase gets stabilized due to part substitution of Th at the Tl-site forx⩾0·25; however,Tc is low forx<0·75.

    • Effect of heat treatment procedures on site preferences of Fe in YBa2Cu3O7−D

      S C Bhargava R Sharma J S Chakrabarty C V Tomy S K Malik

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      Mössbauer spectra of YBa2Cu2·85Fe0:15O7−d prepared using different heat treatment procedures have been obtained. The transition temperature varies from 23 to 53 K, depending on the procedure adopted for preparation. Associated with this are changes in the lattice structure. Mössbauer spectra reveal population of the four components and their relation to the decrease in the transition temperatures.

    • 151Eu Mössbauer studies on Zn-doped EuBa2Cu3O7−y

      C V Tomy R Nagarajan S K Malik Ram Prasad N C Soni Kalyan Adhikary

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      151Eu Mössbauer studies have been performed on the compounds EuBa2(Cu1−xZnx)3O7−y withx=0·0, 0·025, 0·05, 0·075 and 0·1. The parent compound, EuBa2Cu3O7−y is superconducting with a transition temperature (Tc) of 88 K.Tc is depressed as Zn is substituted for Cu in this system and the compounds withx>0·05 do not show superconductivity down to 12 K.151Eu Mössbauer studies at 295 K show a single Mössbauer line in all the compounds (whether superconducting or not) with isomer shift value typical of Eu3 + ion. Further, the isomer shift values are nearly independent ofx and the temperatures down to 10 K. These observations imply that the Cu-O network responsible for superconductivity is very weakly coupled to the Eu sublattice.

    • On the effects of Ti, Zr and Ce substitution in YBa2Cu3O7−δ: transport, XRD, XPS and XANES studies

      P K Mehta B D Padalia O M Prakash D T Adroja P D Prabhawalkar N Venkataramani S K Malik A V Narlikar

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      Results of the XRD, XPS, XANES, iodometric titration and transport studies on freshly prepared Ce, Zr and Ti substituted 1-2-3 samples are reported here. It is argued that at least 2% of Ce, Zr and Ti ions go into the 1-2-3 lattice. It is found that Zr, Ti ions exist in 4+ valence state, Ce is in predominantly 4+ (mixed valence) state and valence of Cu remains unaffected on substitution.

    • Crystal structure and resistivity studies on PrBa2 −xPrxCu3O7 −y oxide system

      S K Malik C V Tomy Ram Prasad N C Soni K Adhikari

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      The compound PrBa2Cu3O7 −y is not superconducting while most other RBa2Cu3O7 −y (R=rare earth) compounds exhibit superconductivity in the 90K range. The system PrBa2 −xPrxCu3O7 −x has been prepared to study the effect of excess Pr at the Ba site on the structure, resistivity and magnetic behaviour of this system. It is observed that single-phase compounds in the above series form forx=0·8—that is up to the composition Pr1·8Ba1·2Cu3O7 −y. While stoichiometric PrBa2Cu3O7 −y is orthorhombic, the compounds with excess Pr show tetragonal structure. Four-probe dc resistivity measurements show that all the single-phase compounds in the above series do not exhibit superconductivity and are semiconducting down to 12 K. Magnetic susceptibility measurements reveal deviation from Curie-Weiss behaviour starting at a characteristic temperature, which is taken to be the ordering temperature (TN) of the Pr moments. BothTN and overall resistivity decrease with increasingx and may have a common origin.

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