• Sadhna Singh

      Articles written in Pramana – Journal of Physics

    • Structural study of Novel (superhard) material: NiO

      Raja Chauhan Sadhna Singh

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      We have investigated the pressure-induced phase transition of NiO and other structural properties using three-body potential approach. NiO undergoes phase transition from B1 (rocksalt) to B2 (CsCl) structure associated with a sudden collapse in volume showing first-order phase transition. A theoretical study of high pressure phase transition and elastic behaviour in transition metal compounds using a three-body potential caused by the electron shell deformation of the overlapping ion was carried out. The phase transition pressure and other properties predicted by our model is closer to the phase transition pressure predicted by Eto et al.

    • Pressure-induced phase transition and stability of EuO and EuS with NaCl structure

      Atul Gour Sadhna Singh R K Singh M Singh

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      We have predicted the phase transition pressures and corresponding relative volume changes of EuO and EuS having NaCl-type structure under high pressure using three-body interaction potential (TBIP) approach. In addition, the conditions for relative stability in terms of modified Born criterion has been checked. Our calculated results of phase transitions, volume collapses and elastic behaviour of these compounds are found to be close to the experimental results. This shows that the inclusion of three-body interaction effects makes the present model suitable for high pressure studies.

    • Theoretical analysis of static properties of mixed ionic crystal: NH4Cl$_{1−x}$Br_{x}$

      D Rawat N K Gaur Sadhna Singh A Gour

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      In the present paper, we have investigated the static properties of the mixed ionic crystal NH4Cl$_{1−x}$Br$_{x}$ using three-body potential model (TBPM) by the application of Vegard’s law. The results for the mixed crystal counterparts are also in fair agreement with the pseudo-experimental data generated from the application of Vegard’s law. The results for the end point members ($x = 0$ and 1) are in good agreement with the experimental data. The results on compressibility, molecular force constant, infrared absorption frequencies and Debye temperature are presented probably for the first time for these mixed crystal counterparts.

    • Structural, electronic, elastic and magnetic properties of heavier $\rm{REIr}_{3}$ ($\rm{RE = Gd, Tb}$ and $\rm{Ho}$) intermetallic compounds

      PUSHPLATA SHUKLA SADHNA SINGH

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      We present results on the bonding nature, structural, electronic, magnetic and elastic properties of $\rm{REIr}_{3}$ ($\rm{RE = Gd, Tb}$ and $\rm{Ho}$) intermetallic compounds adopting simple cubic $\rm{AuCu_{3}}$-type structure obtained using the full-potential linearlised augmented plane wave (FP-LAPW) method based on density functional theory. The local spin density approximation (LSDA) with Hubbard parameter ($\rm{LSDA} +U$) has been used for exchange and correlation effects to get accurate results because of the presence of highly localised $4 f$ electrons of rare-earth $\rm{(RE) (RE = Gd, Tb}$ and $\rm{Ho}$) atoms. The calculated lattice parameter is found to be consistent with the experimental results. The calculated magnetic moments predict ferromagnetic behaviour of these compounds. The electronic and bonding properties have been solved in terms of band structure, density of states (DOS) and charge density plots. These results confirm the metallic nature of these compounds. The bonding appearances of these compounds have also been interpreted from charge density plots. The elastic constants, shear modulus and Cauchy’s pressure are computed and they reveal that $\rm{GdIr_{3}}$ and $\rm{TbIr_{3}}$ compounds are ductile while $\rm{HoIr_{3}}$ shows brittle character.

    • An investigation on the stability of the structural and electronic properties of $ErX_{3} (X = Ga, In\,and\,Sn)$ intermetallic compounds

      PUSHPLATA SHUKLA SADHNA SINGH SANKAR P SANYAL

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      First-principle computations on structural and electronic properties of cubic rare-earth $\rm{ErX_{3} (X = Ga, In\,and\,Sn)}$ intermetallic compounds have been accomplished using the full-potential linearised augmented plane wave (FP-LAPW) method within the framework of density functional theory (DFT). For the exchange correlation, we used local spin density approximation (LSDA) plus Hubbard parameter $U (LSDA+U)$ approach because of the strong on-site Coulomb repulsion between the localised $\rm{RE}-4 f$ states. Calculated ground-state properties such as lattice constant ($a_{0}$) and other parameters with exchange correlation functional are found compatible with the experimental results. The electronic properties have been determined in terms of band structures, total and partial density of states (DOSs) and Fermi surfaces, which demonstrate the metallic behaviour of all the compounds. Also, the effect of Hubbard potential on this is discussed in detail. The bonding descriptions of these compounds have also been evaluated from charge density difference plots, which display the presence of metallic and mixed covalent–ionic bonding. The determined magnetic moments explain the ferromagnetic behaviour of these compounds.

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