Faculty Publications
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Item Investigation of mixed alkali effect on mechanical, structural and thermal properties of three-alkali borate glass system(Elsevier Ltd, 2016) Subhashini, u.; Shashikala, H.D.; Udayashankar, N.K.In the present communication, the results of investigation on mixed alkali effect (MAE) in mechanical, structural and thermal investigation of alkali zinc borate glasses with nominal composition 5Li2O-(25-x)K2O-xNa2O-60B2O3-10ZnO (x = 0, 5, 10, 15, 20 and 25 mol%) are reported. The samples were prepared using standard melt quenching technique. Fourier transform infrared (FTIR) spectroscopy, differential scanning calarometry (DSC) and Vickers indentation studies were performed to investigate the mixed alkali effect in the samples. From the DSC studies, it was observed that the thermal parameters viz., glass transition temperature (Tg), glass melting temperature (Tm), glass crystallization temperature (Tc), glass stability (S) and fragility (F) exhibit a non linear variation with respect to increase in compositional parameter (RNa). This behavior clearly indicated the presence of strong MAE in the samples. FTIR studies confirmed the presence of both [BO3] and [BO4] units, indicating the present glass networks to be made up of these two units placed in different structural groups. The non linear variation of peak positions of B-O-B bending and stretching of [BO3] and [BO4] units of each glass sample explain the role of modifier alkali elements and validates the existence of strong MAE. The microhardness and fracture toughness of the samples were measured using Vickers micro indentation technique and non linear variation of both the properties have been observed confirming the presence of MAE in these glass samples. © 2015 Elsevier B.V.Item 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.Item 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.Item Observation of electrical threshold switching behavior and thermal crystallization in bulk Se86-xTe14Snx chalcogenide glasses(Elsevier Ltd, 2023) Joshi, S.; Udayashankar, N.K.Selenium-rich chalcogenides have gained popularity as materials for selector devices due to their unique Ovonic Threshold Switching behavior. Bulk Se86-xTe14Snx glassy alloys (0 ≤ x ≤ 6) were prepared through the traditional melt quenching method. The samples with Sn atomic percentage (x) = 3 to 6 are found to exhibit a rapid and reversible transition between a highly resistive and conductive state affected by an electric field. A remarkable decrement in threshold voltage (Vth) from 453 V to 62 V has been observed with increase in the Tin content. Differential scanning calorimetry (DSC) analysis was carried out to understand the variation of Glass transition temperature (Tg), Crystallization temperature (Tc), and other important glass stability parameters and their compositional dependence. Se82Te14Sn4 sample was found to be thermally most stable with Herby's parameter value (HR) of 0.3860 and a maximum number of switching cycles at room temperature. X-Ray diffraction patterns of annealed samples were compared with pristine glass to study the multi-phasic Se–Te–Sn alloy. Further, the threshold voltage (Vth) and the number of threshold switching cycles are found to decrease with an increase in temperature till crystallization on-set temperature (Toc). The temperature-dependent conductivity studies showed an abrupt increase in the conductivity of the samples as the temperature crossed the crystallization onset temperature. © 2023 Elsevier Ltd and Techna Group S.r.l.