P S R Krishna
Articles written in Pramana – Journal of Physics
Volume 63 Issue 2 August 2004 pp 183-188
Temperature effects on the structure of liquid D-methanol through neutron diffraction
A Sahoo S Sarkar P S R Krishna R N Joarder
The study of changes in the structure (H-bonded) of liquid alcohols at elevated temperatures is rare probably due to low flash points of these liquids. An indigenously devised special quartz cell is now used to carry out the structural studies of these liquids at elevated temperatures through neutron diffraction. Here, the liquid consists of deuterated methanol and neutron data was collected on the high-
Volume 63 Issue 2 August 2004 pp 213-219
Neutron diffraction studies on La2−
S Rayaprol Rohini Parmar D G Kuberkar Keka R Chakraborty P S R Krishna M Ramanadham
Structural studies on Dy-substituted La-2125 type superconductors have been carried out by neutron diffraction experiments at room temperature using a monochromatic neutron beam of wavelength (λ) = 1.249 Å. A series of samples with La2-xDyxCa2xBa2Cu4+2xOz stoichiometric composition, for
Volume 63 Issue 2 August 2004 pp 221-226
Structure and magnetic properties of colossal magnetoresistance compound Tb0.5Sr0.5CoO3
J S Srikiran A B Shinde P S R Krishna
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 calculated
Volume 63 Issue 2 August 2004 pp 227-232
Low temperature magnetic structure of MnSe
J B C Efrem D'Sa P A Bhobe K R Priolkar A Das P S R Krishna P R Sarode R B Prabhu
In this paper we report low temperature neutron diffraction studies on MnSe in order to understand the anomalous behaviour of their magnetic and transport properties. Our study indicates that at low temperatures MnSe has two coexisting crystal structures, high temperature NaCl and hexagonal NiAs. NiAs phase appears below 266 K and is antiferromagnetically ordered at all temperatures while the NaCl phase orders antiferromagnetically at 130 K.
Volume 63 Issue 2 August 2004 pp 233-237
HgO-added YBa2Cu3O7−δ superconductors
Manglesh Dixit Shovit Bhattacharya Rajneesh Mohan Kiran Singh P S R Krishna Vilas Shelke N K Gaur R K Singh
The HgO-added YBa2Cu3O7−δ (YBCO) superconductor has been studied for its structural and superconducting properties. Polycrystalline YBCO samples were synthesized through solid-state reaction method by adding HgO in different concentrations without using oxygen annealing. All the samples showed a sharp superconducting transition temperature around 90 K. The X-ray diffraction patterns of all the samples revealed monophasic Y-123 nature. The structural studies were carried out by neutron scattering and Rietveld analysis. The neutron scattering revealed that Hg is not incorporated in the Y-123 system and has shown optimum oxygen concentration. The significant role played by the HgO is to provide oxygen ambient through its decomposition, thus changing the oxygen balance in favour of high Cu-valence state.
Volume 63 Issue 2 August 2004 pp 245-249
Neutron scattering study of combustion-synthesized Ce1−
Keka R Chakraborty P S R Krishna M S Hegde
Powder neutron diffraction and Hi-
Volume 63 Issue 2 August 2004 pp 251-255
Low-temperature neutron diffraction study of La0.95Nd0.05CrO3
Keka R Chakraborty S M Yusuf P S R Krishna M Ramanadham A K Tyagi
We have synthesized polycrystalline La0.95Nd0.05CrO3 sample by doping the La-site of LaCrO3 with Nd and its magnetic properties have been studied using DC magnetization and neutron diffraction techniques. DC magnetization study shows a paramagnetic to a weak ferromagnetic-like transition at ∼295 K followed by signatures of a spin reorientation phenomenon at 233 and 166 K and, finally a transition to an antiferromagnetic-like phase at ∼21 K. Low-temperature neutron diffraction measurements confirm a weak ferrimagnetic ordering of Cr3+ moments at all temperatures below 295 K.
Volume 71 Issue 1 July 2008 pp 133-141 Research Articles
A Sahoo S Sarkar P S R Krishna V Bhagat R N Joarder
An analysis of neutron diffraction data of liquid deuterated 1-propanol at room temperature to extract its molecular conformation is presented. Being a big molecule with twelve atomic sites, the analysis is tricky and needs careful consideration. The resulting molecular parameters are compared with electron diffraction (gas phase), X-ray diffraction (liquid phase) and MD simulation results. Information about the hydrogen-bonded intermolecular structure in liquid is extracted and nature of the probable molecular association suggested.
Volume 71 Issue 5 November 2008 pp 929-933 Neutron Diffraction
Structural behaviour of AgNO3 at low temperatures by neutron diffraction
P U Sastry P S R Krishna Lata Panicker A B Shinde
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.
Volume 71 Issue 5 November 2008 pp 935-940 Neutron Diffraction
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
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.
Volume 71 Issue 5 November 2008 pp 941-946 Neutron Diffraction
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
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.
Volume 74 Issue 5 May 2010 pp 765-779 Research Articles
Molecular conformation and liquid structure of 2-propanol through neutron diffraction
A Sahoo S Sarkar P S R Krishna R N Joarder
The neutron diffraction data analysis of deuterated liquid 2-propanol at room temperature to define its molecular conformation is presented. 2-Propanol being a large molecule with twelve atomic sites, the conformation analysis is tricky and an improved method of data analysis is given. The intermolecular structural correlations, i.e., hydrogen-bonded liquid structure, can be modelled accurately to extract the nature of the average hydrogen-bonded molecular association in liquid state at room temperature. Like other alcohols these are mostly hexamer ring chain (HRC) clusters. The cluster analysis of recent X-ray data available in the literature also support the same liquid structure.
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