• Manohar Lal

      Articles written in Pramana – Journal of Physics

    • Electrical properties of nickel-doped arsenic trisulphide

      Navdeep Goyal Rajni Shukla Manohar Lal

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      Results of temperature and frequency dependent a.c. conductivity of pure and nickel-doped a-As2S3 are reported. The a.c. conductivity of pure As2S3 obeys a well-known relationship: σacωs. Frequency exponents is found to decrease with increasing temperature. Correlated barrier hopping (CBH) model successfully explains the entire behaviour of a.c. conductivity with respect to temperature and frequency for pure As2S3. But a different behaviour of a.c. conductivity has been observed for the nickel doped As2S3. At higher temperatures, distinct peaks have been observed in the plots of temperature dependence of a.c. conductivity. The frequency dependent behaviour of a.c. conductivity (σacωs) for nickeldoped As2S3 is similar to pure As2S3 at lower temperatures. But at higher temperatures, ln σac vs lnf curves have been found to deviate from linearity. Such a behaviour has been explained by assuming that nickel doping gives rise to some neutral defect states (D0′) in the band gap. Single polaron hopping is expected to occur between theseD0‘ andD+ states. Furthermore, allD+,D0′ pairs are assumed to be equivalent, having a fixed relaxation time at a given temperature. The contribution of this relaxation to a.c. conductivity is found to be responsible for the observed peak in the plots of temperature dependence of a.c. conductivity for nickel-doped As2S3. The entire behaviour of a.c. conductivity with respect to temperature and frequency has been explained by using CBH and “simple pair” models. Theoretical results obtained by using these models, have been found to be in agreement with the experimental results.

    • Relation of coordination number to memory and threshold switching in chalcogenides

      Manohar Lal Navdeep Goyal Anil Vohra

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      The paper reports a structural study of some memory and threshold chalcogenides in terms of coordination numberC, defined byC=8−N, and is the average coordination number for covalently bonded materials. The average number of nearest neighbours surrounding a central atom, obtained for As-Ge-Te (memory) and Se-Ge-Te (threshold) systems have been used to estimate the cohesive energies, assuming simple additivity of bond energies. The bonding pattern so obtained, explains certain properties of these glasses.

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