• S N Achary

      Articles written in Pramana – Journal of Physics

    • 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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