• N R SANJAY KUMAR

      Articles written in Bulletin of Materials Science

    • High-pressure studies on pristine and Pb-substituted Bi-based high-temperature superconductor

      V GAYATHRI A T SATHYANARAYANA BALMUKUND SHUKLA T GEETHA KUMARY N R SANJAY KUMAR SHARAT CHANDRA

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      Transport measurements were performed on over-doped samples of pristine and Pb-substituted Bi–Sr–Ca–Cu–O as a function of applied pressure up to 7 GPa. A monotonic decrease in the superconducting transition temperature accompanied by a change in the normal-state behaviour from metallic to semiconducting as a function of pressure is observed in the pristine sample. In the Pb-substituted sample, a monotonic decrease in the superconducting transition temperature up to ${\sim}$4.5 GPa followed by an increase after attaining a valley is observed. The pressure required to achieve this increase in T$_C$ in the Pb-substituted Bi–Sr–Ca–Cu–O was found to be much lower than that reported in the literature. High-pressure X-ray diffraction measurements performed on these samples reveal the absence of any structural phase transition. Furthermore, the values of the bulk moduli are found to increase in the Pb-substituted sample. The density functional theory calculations used to substantiate the obtained results indicate a pressure-induced buckling of the Cu–O plane in the Bi-2212 phase of the pristine sample. In the Pb-substituted sample, an increase in the number of electronic states available for conduction at the Fermi level and a pressure-dependent increase in the contribution of Pb towards the density of states are revealed from the calculations of the density functional theory.

    • Compressibility studies of RE$_6$UO$_{12}$ at extreme conditions of pressure

      BALMUKUND SHUKLA N R SANJAY KUMAR HRUDANANDA JENA ANUJ UPADHYAY N V CHANDRA SHEKAR

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      Rare-earth uranates-RE$_6$UO$_{12}$ are synthesized by heating mixture of uranium oxide and rare-earth oxides in 1:6 ratio above 1273 K. These compounds stabilize in rhombohedral structure at ambient. High-pressure (HP) X-ray diffraction studies reveal that the compounds are stable at lower pressures, beyond which disorder is seen to originate and compound has a tendency to amporphize at very HPs. The a-axis of the lattice is found to be more rigid as compared to c-axis because of corner sharing polyhedra along a-axis. Anomalous compressibility behaviour is seen in Gd$_6$UO$_{12}$, where sharp decrease in the bulk modulus is observed. The behaviour is against the normal trend of compressibility in RE$_6$UO$_{12}$ compounds along rare-earth cation series.

    • High pressure investigations on neutron irradiated ferroboron

      ANAND KUMAR UTTYIOARNAB SAHA E RADHA K DEVAN N R SANJAY KUMAR C N VENKITESWARAN R DIVAKAR N V CHANDRA SHEKAR

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      This study reports the pressure effect on structural stability of neutron irradiated ferroboron systems. Ferroboron, a mixture of boron and iron, has been found to have three phases, i.e., FeB, Fe$_2$B and Fe$_3$B. Studies have been conducted on single-phase Fe$_2$B and ferroboron. Fe$_2$B adopts tetragonal structure at ambient and undergoes structural transition to orthorombhic phase at 6 GPa. Further, Fe2B is irradiated with neutrons with a fluence of ${\sim}$10$^{17}$ n cm$^{–2}$ and yields bulk modulus of 254 GPa, which is 16% enhancement as compared to unirradiated sample. The defects are estimated by the use of SRIM code. Total displacement per atom (dpa) in Fe$_2$B for the irradiation fluence is found to be 5.53${\times}$10$^{-5}$. The study also shows that phase transition seen in pristine Fe$_2$B is inhibited upon neutron irradiation under pressure up to 24 GPa. Similar result was obtained on ferroboron mixture, irradiated with a neutron fluence of 8.18${\times}$10$^{21}$ n cm$^{-2}$ with dpa of 2.8. The irradiated sample is found to be stable up to 16 GPa.

    • Correction to ‘High pressure investigations on neutron irradiated ferroboron’

      ANAND KUMAR UTTIYOARNAB SAHA E RADHA K DEVAN N R SANJAY KUMAR C N VENKITESWARAN R DIVAKAR N V CHANDRA SHEKAR

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      Posted on October 12, 2020

      Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
      Chemical Sciences 2020

      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
      Physical Sciences 2020

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