• N Kaurav

      Articles written in Bulletin of Materials Science

    • Pressure dependence of elastic properties of ZnX (X = Se, S and Te): Role of charge transfer

      Dinesh Varshney P Sharma N Kaurav R K Singh

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      An effective interaction potential (EIOP) is developed to invoke the pressure induced phase transition from zinc blende (𝐵3) to rocksalt (𝐵1) structure and anharmonic properties in ZnX (X = Se, S, Te) semiconductors. The effective interaction potential incorporates the long range Coulomb interaction, van der Waals interaction and short-range repulsive interaction up to second neighbour ions within the Hafemeister and Flygare approach as well as the charge transfer effects caused by the electron-shell deformation of the overlapping ions. The van der Waals coefficients are computed by the Slater Kirkwood variation method as a first step. Later on, we evaluate volume collapse, second order and third order elastic constants with pressure pointing to the systematic trends in all compounds of zinc blende structure and their thermal properties such as force constant, Gruneisen parameter, compressibility, Debye temperature etc. The vast volume discontinuity in pressure–volume (PV) phase diagram identifies the structural phase transition from zinc blende (𝐵3) to rock salt (𝐵1) structure and is consistent with those revealed from earlier reports.

    • Spin fluctuation and small polaron conduction dominated electrical resistivity in La0.875Sr0.125MnO3 manganite nanostructures

      K K Choudhary N Gupta N Kaurav S Katiyal S K Ghosh

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      The anomalous temperature-dependent electrical resistivity ρ(𝑇) of La0.875Sr0.125MnO3 manganite nanoparticles (particle size 18 nm) is theoretically analysed. ρ(𝑇) exhibits semiconducting phase in lowtemperature regime (20 𝐾 < 𝑇 < 53 K), shows a minima near 53 K and increases with 𝑇 at high temperatures (53 𝐾 < 𝑇 < 170 K). The resistivity in metallic phase (𝑇 > 53 K) is theoretically analysed by considering the strong spin-fluctuation effect, which is modelled using Drude–Lorentz type function. In addition to the spin fluctuation-induced contribution, the electron–phonon and electron–electron $ ρe–e(𝑇) = 𝐵𝑇2 contributions are also incorporated for complete understanding of experimental data. The contributions to the resistivity by inherent acoustic phonons ( ρac) as well as high-frequency optical phonons ( ρop) were estimated using Bloch–Gruneisen (BG) model of resistivity. It is observed that the resistivity contribution due to electron–electron interaction shows typical quadratic temperature dependence. Spin fluctuation-induced resistivity is dominant over electron–electron and electron–phonon contributions in overall temperature range in the manganite nanoparticles. Resistivity in the semiconducting phase is discussed with small polaron conduction (SPC) model. SPC model consistently retraces the low-temperature resistivity behaviour (𝑇 < 53 K). Finally, the theoretically calculated resistivity compared with experimental data is found to be consistent in wide range of temperature.

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