• D K Kulkarni

      Articles written in Bulletin of Materials Science

    • CuAlMnO4 from two different combinations and their structural and electrical study

      A B Devale H S Bisht D K Kulkarni

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      A compound CuAlMnO4 has been synthesised for the first time by oxide method using 1+ and 2+ copper oxides separately. Both the compounds crystallise in tetragonal unit cell witha=8·205 A andc=8·342 A. It has been observed that there are similarities in structures but dissimilarities in their electrical behaviours. The observed tetragonal symmetry, lattice dimensions and electrical behaviour are explained on the basis of solid solution of CuAl2O4 and CuMn2O4 spinels.

    • Structural, magnetic and electrical study of MgCoMnO4

      S G Joshi D K Kulkarni P V Khandekar

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      A new compound MgCoMnO4 has been synthesised by the oxide method. It crystallizes in a tetragonal spinel structure witha=8.30 A andc=8.46 A. The observed crystal symmetry is associated with the existence of Mn+3 on theB sites. The compound isn type semi-conductor with activation energy ΔE=0.33 eV. The electrical properties show that it can be regarded as a properly substituted MgMn2O4 by Co+3 ions. It is paramagnetic withCM=5.75 and ϑa =−160°K. All these results show the ionic configuration of the compound as Mg+2 [Co+3 Mn+3] O4.

    • Structural, magnetic and electrical study of CoMnAlO4

      S G Joshi D K Kulkarni P V Khandekar

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      A spinel CoMnAlO4 has been synthesised by the oxide method. It has a tetragonal structure withA=8.10 A andC=8.22 A. A break is found in the plot of logρ against 1/T at 573°K when activation energy changes from 0.62 eV to 0·52 eV. The electrical properties show that it can be regarded as a properly substituted CoMn2O4 by Al+3 ions. It is paramagnetic withCM = 4.72 and ϑa= −298°K. These results show the ionic configuration of the compound as Co+2 [Mn+3 Al+3]O4.

    • New formula for lattice dimension of an oxide spinel with cubic structure

      G M Bhongale D K Kulkarni V B Sapre

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      An empirical relation between lattice parameter and cationic radii for cubic spinels has been established by considering the packing of anions in non-ideal situation and ionic displacement parameter (δ =u−3/8). This relation gives the value ofa, the lattice parameter, which is much closer to the observed value.

    • EXAFS: Determination of cation distribution in spinels

      G M Bhongale V B Sapre D K Kulkarni

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      In oxidic spinels containing transition metal ions, the tetrahedral and octahedral bond distances differ by less than 0·25 Å. Therefore, in the case of a cation occupying both the sites, the normalized EXAFS for first coordination shell gives the average bond distance and average coordination number respectively over all the bonds and the positions of the cation under investigation. EXAFS analysis of fourteen mixed lithium ferrite spinels was carried out to show how the average bond distance can fruitfully be used to obtain the exact cation distribution, in conformity with X-ray diffraction data.

    • Structural and magnetic properties of CaAl4Fe8O19

      D K Kulkarni C S Prakash

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      A new compound, CaAl4Fe8O19, was synthesized for the first time and characterized by X-ray diffraction. It was found to have a hexagonal magnetoplumbite structure with lattice parametersa=5·83 Å andc=22·14 Å. The electrical studies showed that the compound was a semiconductor with energy of activationq=0·86 eV. The magnetic susceptibility was studied in the temperature range 300 K to 850 K, in which the compound was paramagnetic with a Curie molar constant of 31·03.

    • Crystallographic and electrical study of the chromium substituted ferrous zinc copper ferrites

      V M Nanoti D K Kulkarni

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      The structural and electrical properties of the oxidic spinel Zn0·5Cu0·5FexCr2−xO4 (x=0·8, 0·9, 1·0, 1·1) have been investigated through X-ray diffraction, electrical resistivity, and thermoelectric measurements.

      X-ray diffraction data showed formation of single spinel phase with cubic structure. D.C. resistivity measurements from room temperature to 850 K was carried out and activation energy for all the compositions evaluated. Thermoelectric measurements showedp-type semiconducting nature in all the samples.

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