• A B Shinde

      Articles written in Pramana – Journal of Physics

    • Structure and magnetic properties of colossal magnetoresistance compound Tb0.5Sr0.5CoO3

      J S Srikiran A B Shinde P S R Krishna

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      The structure and the magnetic properties of the doped rare earth cobaltite systems are of recent interest owing to the CMR phenomenon that occur in them. In this paper, we investigate the structure and magnetic properties of Tb0.5Sr0.5CoO3 solid solution, for the first time, using neutron powder diffraction technique. The sample Tb0.5Sr0.5CoO3 is found to crystallize in orthorhombic (Pbnm) symmetry. The unit cell volume and Co—O bond length reduce with temperature. The calculatedeg bandwidth obtained from structural parameters turns out to be 0.989 eV. Low temperature neutron diffraction profiles exhibit a magnetic contribution to the fundamental Bragg peaks indicating a ferromagnetic ordering belowTc. The results are compared with Co—O—Co bond angles and Co—O bond length of La0.5Sr0.5CoO3, highlighting the ionic size effects on substitution of Tb ion for La in the compound.

    • Structural behaviour of AgNO3 at low temperatures by neutron diffraction

      P U Sastry P S R Krishna Lata Panicker A B Shinde

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      Structural behaviour of silver nitrate (AgNO3) at low temperatures has been investigated by neutron powder diffraction and differential scanning calorimetry (DSC). Analysis showed abnormal changes in the rotations of nitrate (NO3) anions and thermal displacement parameters of the atoms near 220 K and 125 K. However, the basic lattice is compatible with the orthorhombic symmetry (space group Pbca) till 12 K. The fine, small-scale structural anomalies probably originate from freezing of reorientation of NO3 ions from high-temperature disordered phase.

    • Cation disorder and structural studies on Bi$_{4−x}$Nd$_{x}$Ti3O12 $(0.0 \leq x \leq 2.0)$

      S N Achary S J Patwe P S R Krishna A B Shinde A K Tyagi

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      Here we report the results of combined powder X-ray and neutron diffraction studies of Bi$_{4−x}$Nd$_{x}$Ti3O12 $(0.0 \leq x \leq 2.0)$ compositions. The parent Bi4Ti3O12 has an orthorhombic lattice (space group: B2cb) with unit cell parameters $a$ = 5.4432(5) Å, $b$ = 5.4099(5) Å and $c$ = 32.821(2) Å, and $V$ = 966.5(1) Å3. This orthorhombic lattice is retained in all the studied compositions. The unit cell parameters gradually decrease with Nd 3+ ion concentration with a discontinuity at $x = 0.75$. Orthorhombicity of the lattice decreases with increase in Nd3+ content in the lattice. The orthorhombic unit cell parameters for a representative Bi2Nd2Ti3O12 composition are: $a$ = 5.3834(9), $b$ = 5.3846(9) and $c$ = 32.784(1) Å. The observed orthorhombic distortion at $x$ = 2.0 is very small and thus the crystal structure apparently has a pseudo-tetragonal lattice. In addition, Nd3+ preferentially substitutes in the perovskite slab of the Aurivillius structure. The fraction of Nd3+ in the fluorite slab increases with increase in Nd3+ contents.

    • Neutron diffraction studies on Ca$_{1-x}$Ba$_{x}$Zr4P6O24 solid solutions

      S N Achary O D Jayakumar S J Patwe A B Shinde P S R Krishna S K Kulshreshtha A K Tyagi

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      Herein we report the results of detailed crystallographic studies of Ca$-[1-x}$Ba$_{x}$Zr4P6O24 compositions from combined Rietveld refinements of powder X-ray and neutron diffraction data. All the studied compositions crystallize in rhombohedral lattice (space group R-3 No. 148). A continuous solid solution is concluded from the systematic variation of unit cell parameters. The variation of unit cell parameters with the composition indicates decreasing trend in 𝑎 parameter with increasing Ba2+ concentration contrast to an increasing trend in 𝑐 parameter.

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