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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]

The effect of a lithium salt on the general polymer dynamics of poly(ethylene oxide) (PEO) and how these dynamical alterations affect the ionic conductivity and structural relaxations in (PEO)4:LiClO4 have been investigated. The study was based on differential scanning calorimetry (DSC) and dielectric relaxation studies. The DSC studies indicated an increased glass transition temperature of (PEO)4:LiClO4 as compared to that of PEO. The polymer-salt complex exhibited enhanced conductivity of σD.C. =3.2×10−7 S·cm−1 at room temperature (298K) due to the presence of mobile Li+ ions. Impedance data have been scaled and analyzed under conductivity and modulus formalisms over wide ranges of frequency and temperature for both PEO and (PEO)4:LiClO4. For PEO, the analysis of the scaled formalisms indicates that both the conductivity and the structural relaxation mechanisms are temperature-independent above the melting point of PEO. However, below the melting point, the nucleation and growth of spherulites and also the formation of ‘interphase’ regions in PEO result in a hindered long range D.C. conductivity, which, in turn, leads to a decoupling of the D.C. conductivity and the structural relaxation. However, for (PEO)4:LiClO4, by comparing the conductivity relaxation data with the calorimetric glass transition and analysis of scaled formalisms, a direct coupling between Li+ ion motions and polymer segmental dynamics is observed for the polymer electrolyte. [ABSTRACT FROM AUTHOR]

Abstract: Conduction characteristics of the poly(ethylene oxide) based new polymer electrolyte (PEO)6:NaPO3, plasticized with poly(ethylene glycol) are investigated. Free standing flexible electrolyte films of composition (PEO)6:NaPO3 + x wt.%PEG400 (30⩽ x ⩽70) are prepared by solution casting method. A combination of X-ray diffraction (XRD), optical microscopy and differential scanning calorimetry (DSC) studies have indicated enhancement in the amorphous phase of polymer due to the addition of plasticizer. Further, a reduction in the glass transition temperature observed from the DSC result has inferred increase in the flexibility of the polymer chains. The cationic transport number of 0.42 determined through combined ac–dc technique has confirmed ionic nature of conducting species. Ionic conductivity studies are carried out as a function of composition and temperature using complex impedance spectroscopy. The electrolyte with maximum PEG400 content has exhibited an enhancement in the conductivity of about two orders of magnitude compared to the host polymer electrolyte. The complex impedance data is analyzed in conductivity, permittivity and electric modulus formalism in order to throw light on transport mechanism. A solid state electrochemical cell based on the above polymer electrolyte with a configuration Na|SPE|(I2 +acetylene black+PEO) has exhibited an open circuit voltage of 2.94V. The discharge characteristics are found to be satisfactory as a laboratory cell. [Copyright &y& Elsevier]

Abstract: Sodium borophosphate glasses of composition (mol%) 50Na2O–50[xB2O3–(1-x)P2O5], 0≤x≤0.8 have been prepared by melt quenching method and characterized through XRD, DSC, FTIR and impedance spectroscopy techniques. The glass transition temperature increases with the substitution of B2O3 due to the cross-linking of the network and the FTIR study shows the presence of different structural units in the network. The ionic conductivity study as a function of composition of B2O3 shows increment in conductivity with two conductivity maxima at 10 and 30mol% of B2O3 and conductivity variations with temperature follow an Arrhenius type behaviour. Transport numbers evaluated for ions and electrons show that Na+ ions are the mobile species in the investigated systems. The frequency dependence of the electric conductivity follows a simple power law feature. The analysis of various electrical parameters as a function of temperature in different complex planes shows that the charge transport occurs by the hopping mechanism. [Copyright &y& Elsevier]