• D Kumar

      Articles written in Bulletin of Materials Science

    • Pre-exponential factor in 𝑎-Se75In25–𝑥Pb𝑥 thin films

      D Kumar S Kumar

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      Temperature dependence of d.c. conductivity is studied in 𝑎-Se75In25–𝑥Pb𝑥 thin films where 𝑥 is varied from 0–10. From these measurements, the values of the pre-exponential factor (𝜎0) and activation energy (𝛥𝐸) are calculated for each glassy alloy. An approximate linear dependence of ln 𝜎0 on 𝛥𝐸 is observed in this glassy system with good agreement between the expected and calculated 𝜎0 values using Meyer–Neldel rule. Linear dependence of ln𝜎0 on 𝛥𝐸 in case of amorphous materials indicates that the conduction band tails a finite energy distance towards the valence band and Fermi level is controlled by fixed dominant hole levels deeper in the gap.

    • Synthesis, IR, crystallization and dielectric study of (Pb, Sr)TiO3 borosilicate glass–ceramics

      C R Gautam D Kumar O Parkash Prabhakar Singh

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      Eleven glass compositions were prepared by melt and quench method with progressive substitution of SrO for PbO (0 ≤ 𝑥 ≤ 1.0) with a step-wise increment of 0.10 in the glass [(Pb𝑥Sr1−𝑥)OTiO2]–[(2SiO2B2O3)]–[BaO.K2O].Nb2O5 (mol percentage) system. The infrared spectra (IR) of various glass compositions in the above mentioned glass system was recorded over a continuous spectral range 400–4000 cm-1 to study their different oxides structure systematically. Differential thermal analysis (DTA) was recorded from room temperature (∼27 °C) to 1400 °C employing a heating rate of 10 °C/min to determine glass transition temperature, 𝑇g and crystallization temperature, 𝑇c. The melting temperature, 𝑇m, of these glass compositions was found to be in the range 597–1060 °C depending on the composition under normal atmospheric conditions. 𝑇g and 𝑇m of glasses were found to increase with increasing SrO content. X-ray diffraction analysis of these glass–ceramic samples shows that major crystalline phase of the glass–ceramic sample with 𝑥 ≤ 0.5 was found to have cubic structure similar to SrTiO3 ceramic. Scanning electron microscopy has been carried out to see the surface morphology of the crystallites dispersed in the glassy matrix.

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