• A K Rastogi

      Articles written in Bulletin of Materials Science

    • Phase transitions in molybdenum sesquisulphide systems between 80 and 600 K

      A K Rastogi R K Ray

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      Samples of Mo2S3 system and substituted derivatives with Cr, Nb, Cu and Mn have been studied. The resistivity, thermoelectric power, magnetic susceptibility and specific heat indicate clear phase transition at temperatures between 200 and 310 K. X-ray investigations establish the transitions at these temperatures as structural changes. Careful analysis of the data helps to obtain working values for a model for the energy band. Carrier density, effective mass, mobility, band overlap parameter, density of states for the electrons and holes in the overlapping bands at the Fermi level and the band gap for a higher conduction band are obtained.

    • Evidence for the complicated Fermi surface in 2H- and 4H-NbSe$_2$

      I NAIK A K RASTOGI

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      In this study, we have found superconducting state (SC) at 7.4 and 6.4 K and charge density wave state (CDW) at 35 and 42 K in our 2H- and 4H-NbSe$_2$ single crystals, respectively. Besides this, there exists a positive magneto-resistance (MR) below the CDWtransition temperature on both the crystals. Therefore, we have calculated their fractional change in MR i.e., $\Delta \rho/\rho_0$ around 8 K in $H_{\perp}$ plane of NbSe$_2$ and $H_{\parallel}$ plane of NbSe$_2$ configurations. Both single crystals show anisotropic $\Delta \rho/\rho_0$, which are described by Kohler’s rule, two-band model and magnetic breakdown model. In the present scenario, the magnetic breakdown model explains our anisotropic $\Delta \rho/\rho_0$ better than other two models: Kohler’s and two-band model. This model also established the presence of complicated Fermi surface on both single crystals.

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