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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: Thermal, structural and ionic conduction characteristics of lithium niobophosphate glass (mol% 50Li2O–45P2O5–5Nb2O5) are reported and compared with the characteristics of lithium metaphosphate glass (mol% 50Li2O–50P2O5). The presence of the second glass former (Nb2O5) not only improves the chemical durability and thermal stability but also enhances the conduction characteristics of lithium metaphosphate glass. The ionic conductivity measurements are reported in the extended temperature range i.e. above the glass transition temperature (Tg) where a non-Arrhenius temperature dependence of the ionic conductivity has been observed. The ion conduction process below Tg is governed by a well-defined activation energy whereas the conduction process above Tg is activated by at least two different phenomena discussed in the light of the structural relaxation and crystallization. [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: Investigations on the glass system mol% 50Li2O:(50− x)P2O5:xB2O3 reveal that the glass forming region is limited to a small region of 0≤ x ≤20. Addition of B2O3 is found to enhance the thermal stability of the glasses. Raman spectra reveal that the glass matrix undergoes structural modification for x ≥15, with the formation of borophosphate structural units, due to the presence of which, the glass composition 50Li2O: 30P2O5: 20B2O3 has exhibited dc conductivity value of 1.8×10−5 S cm−1, when compared to the value of 8.4×10−7 S cm−1 of 50Li2O: 50P2O5 at 110 °C. Though ball milled sample for x =15 initially exhibited better conduction characteristics than melt quenched ones, the conductivity decreased during thermal cycling process probably due to the phase instability of the milled samples. The frequency dependent conductivity plots have been scaled to a single master curve indicating temperature independent relaxation mechanism. [Copyright &y& Elsevier]