Search

Abstract: The main aim of the present study is to investigate the effect of second glass modifier Na2O on the crystallization kinetics and thermal stability of the mol% xNa2O:(50−x)Li2O:50P2O5 glasses, where Li+ ions are progressively substituted with Na+ ions, using differential scanning calorimetry. The DSC studies showed the classical ‘mixed alkali effect’ on the glass transition temperature, with the Tg minima for the glass composition of [Na+/(Li++Na+)]=0.5 i.e. x =25mol%. The crystallization temperature decreases as Na+ ions completely replaces Li+ ions. The presence of small concentration of second alkali (either the guest ion or host ion) tends to enhance the thermal stability, S, against devitrification as observed for 5≤ x ≤15 and 37.5≤ x ≤45. The ‘mixed alkali effect’ tends to thermally stabilize the intermediate compositions of mol% xNa2O:(50−x)Li2O:50P2O5 as these compositions exhibited high S parameter, high activation energy for crystallization and low enthalpy of crystallization, ΔHc. [Copyright &y& Elsevier]

Abstract: Crystallization kinetics of bulk and pulverized glass samples of the system mol% 50Na2O:50P2O5 have been investigated through isothermal as well as non-isothermal DSC studies. Analysis of the crystallization exotherms reveals that the bulk sodium metaphosphate glass undergoes single-stage crystallization with an order parameter (Avrami constant) of 2.7±0.1 and an activation energy for crystallization equal to 142.5kJ/mol, suggesting internal (bulk) crystallization of the glass. The activation energy for structural relaxation, evaluated by the analysis of the dependence of T g on different heating rates, turns out to be 534.8kJ/mol. The exotherm peaks of pulverized glasses exhibit a shift in the crystallization temperature, T c along with a change in the height and width of the peak. The pulverized glass sample undergoes surface crystallization, with almost the same value of activation energy for crystallization as that of bulk glass. The single-stage crystallization mechanism of sodium metaphosphate (bulk and pulverized) glass is closely associated with Johnson–Mehl–Avrami (JMA) model. [Copyright &y& Elsevier]

Abstract: An intercalation compound with composition Na0.7CoO2 has been synthesized through different preparative techniques such as solid state reaction, ball milling and sol gel techniques. The investigation reveals that the cathode material with an average particle size of about 500nm of uniform morphology can be synthesized through sol gel technique. Further, this synthesis technique improves the stoichiometry of the sodium content significantly. The electrical resistivity of these cathode materials is found to be in the range of 4 to 12mΩ-cm at 300K. It has been observed that, the resistivity of the cathode material increases with increase in sodium content. The electrochemical cells with the configuration Na | [wt.% 0.3 PEO-0.7 PEG]6:NaPO3 |composite cathode material, have shown an open circuit voltage (OCV) value of 2.7V. The (OCV) of the cells with the cathode prepared by sol–gel and ball milling route has shown a plateau region of about 40h, when compared to the plateau region of 10h for the battery with the cathode prepared by solid state reaction. The reduction in the particle size of the cathode material has improved the stability of the electrode electrolyte interface and thereby discharges characteristics. [Copyright &y& Elsevier]

Abstract: Sodium pentafluorodistannite has been synthesized through high-energy ball milling as well as by solid-state reaction method and characterized through XRD and DSC techniques. The electrical conductivity and modulus characteristics of the system are investigated in the temperature range from 373K to 473K by means of impedance spectroscopy. The conductivity of the ball-milled sample is about one order of magnitude higher compared to the sample prepared by solid-state reaction method. The frequency dependent conductivity of the present system shows the power law feature. The real part of dielectric permittivity shows a huge value at lower frequencies due to the presence of space charge polarization. The activation energy responsible for relaxation calculated from the modulus spectra is found to be almost the same as the value obtained from temperature variation of dc conductivity. The conductivity and modulus spectra of the present system show scaling behavior, which means that σ*(ω) and M″(ω) isotherms successfully collapse to a single master curve indicating temperature independent relaxation behavior. [Copyright &y& Elsevier]

The composite solid electrolytes, NaNO3 dispersed with Al2O3, CeO2, ZrO2 and SiO2 have been prepared by melt quenching method and investigated through XRD, DSC and electrical conductivity techniques. Typical increase in conductivity is about two orders of magnitude for 10 mol% of Al2O3 at 200 °C. The electronic transference number evaluated through dc polarization method was found out to be 1×10−2 at 200 °C. The dependence of conductivity on concentration of dispersoids and particle size is in accordance with the space charge theory of conduction. The enhanced conductivity of NaNO3 homogenously doped by Ca(NO3)2 was further enhanced by heterogeneous doping of Al2O3. By the contribution of these doping processes, the conductivity is enhanced by three orders of magnitude at 200 °C. The experimental and theoretically calculated values of conductivity using Maier''s space charge layer model are in reasonable agreement. [Copyright &y& Elsevier]