Faculty Publications

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Author: search.filters.author.Ramesh, K.Subject: search.filters.subject.Activation energy

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    Thermal stability and crystallization kinetics of Bi doped Si15Te85-xBix (0 ≤ x ≤ 2) chalcogenide glassy alloys
    (Elsevier Ltd, 2018) Fernandes, B.; Munga, P.; Ramesh, K.; Udayashankar, N.K.
    Bulk Si15Te85-xBix (0 ≤ x ≤ 2) chalcogenide glassy alloys were prepared by well-established melt quenching technique. Thermal stability and crystallization kinetics of these alloys were investigated by employing differential scanning calorimetry (DSC) technique at different heating rates, namely, 10, 15, 20 and 25 K/min under non-isothermal condition. Thermal parameters such as glass transition (Tg), onset crystallization (Tc) and peak crystallization (Tp) temperatures were observed. Double crystallization peaks observed in the DSC thermogram refer to the instability and phase separated network in the glasses. Various kinetic parameters such as thermal stability (ΔT), enthalpy (ΔHc), entropy (ΔS), specific heat (ΔCp) and fragility index are deduced. The calculated kinetic parameters suggest that the stability of glassy samples decreases with the increase in Bi addition. The activation energies of glass transition (Eg), and crystallization (Ec) are calculated using relevant kinetic formulae. We further discuss on the kinetics of the synthesized materials relevant for their applications in phase change memory (PCM) material. © 2017 Elsevier Ltd.
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    Crystallization kinetics of Sn doped Ge20Te80?xSnx (0 ? x ? 4) chalcogenide glassy alloys
    (Elsevier Ltd, 2017) Fernandes, B.J.; Naresh, N.; Ramesh, K.; Sridharan, K.; Udayashankar, N.K.
    Chalcogenide semiconductors have evolved as multifunctional materials due to their fascinating thermal, optical, electrical and mechanical properties. In this report, Ge20Te80?xSnx (0 ? x ? 4) glassy alloys are systematically studied in order to understand the effect of variation of Sn content on the thermal parameters such as glass transition (Tg) onset crystallization (Tc), peak crystallization (Tp), melting temperature (Tm), activation energy of glass transition (Eg), and crystallization (Ec). The values of Eg are calculated from the variation of Tg with the heating rate (?), according to Kissinger and Moynihan model, while the values of Ec are calculated from the variation of Tp with the heating rate (?), according to Kissinger, Takhor, Augis-Bennett and Ozawa model. Thermal stability and glass forming ability (GFA) are discussed for understanding the applicability of the synthesized materials in phase change memory (PCM) applications. Thermal parameters are correlated with the electrical switching studies to get an insight into the phase change mechanism. The results of the calculated thermal parameters reveal that the GFA of the synthesized Ge20Te80?xSnx (0 ? x ? 4) glassy alloys has a synchronous relationship with their thermal properties studied through differential scanning calorimetry, indicating their potential for phase-change memory device applications. © 2017 Elsevier B.V.
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    Crystallization kinetics of Si20Te80?xBix (0???x???3) chalcogenide glasses
    (Elsevier Ltd, 2019) Fernandes, B.J.; Ramesh, K.; Udayashankar, N.K.
    In this report, we investigate the crystallization kinetics of Si20Te80?xBix (0 ? x ? 3) chalcogenide glassy systems using differential scanning calorimetry (DSC) technique. Systematic studies are carried out in order to understand the variation of thermal parameters such as glass transition temperature (Tg), onset crystallization temperature (Tc) and peak crystallization temperature (Tp) as a function of composition. Activation energy for glass transition (Eg) and crystallization (Ec) has been calculated based on the relevant statistical methods. Furthermore, thermal parameters such as change in specific heat (?Cp), fragility index (F), thermal stability (?T)& (S), enthalpy (?Hc), entropy (?S) are deduced to interpret distinct material behaviour as a function of composition. Structural evaluation like thermal devitrification studies elucidate the restricted glass formability of the studied glass system. Conclusively, a relationship has been established between the obtained thermal parameters and electrical switching characteristics. © 2019 Elsevier B.V.