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Conductivity relaxation using modulus formalism has been used to explore the coupling of ionic conductivity to dielectric relaxation in polymer electrolyte based on polyethylene oxide complexed with various content of LiAsF6. The temperature dependence of conductivity followed the VTF behavior suggesting close correlation between conductivity and the segmental relaxation process in polymer electrolytes. The coupling of conductivity to the segmental process has been discussed in terms of coupling index. For all compositions studied, the coupling index was within the range of 1-11 in the temperature range of investigation, which was in agreement with the coupled systems. [ABSTRACT FROM AUTHOR]

Abstract: The effect of plasticizer (polyethylene glycol, PEG200) on dielectric and electrical properties of an ionically conducting polymer nanocomposites PEO25-NaI+5wt.% DMMT (dodecyl amine modified Na+-montmorillonite)+ x wt.% PEG200 with different value of x has been investigated. At low frequency, the variation of relative dielectric constant with frequency shows the presence of material electrode interface polarization processes. The tangent loss peaks appearing at a characteristic frequency suggest the presence of relaxing dipoles in all the samples. On addition of plasticizer, the peak shifts towards higher frequency side suggesting the speed up the relaxation time. The electrical modulus formalism is used to study the ionic relaxation processes in these composites in terms of conductivity relaxation time. Analysis of electrical modulus and dielectric permittivity functions suggest that ionic and polymer segmental motions are strongly coupled. The frequency dependence of ac conductivity follows the universal power law with a small deviation in the low frequency region due to the electrode polarization effect. [Copyright &y& Elsevier]

Abstract: Structural, microstructural and electrical properties of lanthanum-modified sodium bismuth titanate (Na0.5Bi0.5TiO3) (NBT) ceramics were investigated. X-ray diffraction (XRD) analysis of the prepared materials confirmed the formation of the compounds with rhombohedral crystal system. The nature of scanning electron micrographs of the compounds showed (i) the uniform distribution of grains on the sample surface with high density and (ii) reduction of grain size on La substitution at the (Na of NBT. Detailed studies of dielectric and impedance properties of the materials, carried out in the frequency range of 102–106 Hz at different temperatures (room temperature to 500°C), have provided many interesting properties. The dielectric constant at transition temperature was found to be decreased with increase of broadening of the dielectric peak on increasing La content in the sample. The transition temperature (T m) shifted to higher temperature side on addition of La (up to 6%), whereas the reverse trend was observed for higher concentration of La (i.e. 8%). The depolarization temperature (T d) of La-modified NBT compounds was found to be smaller than that of pure NBT. The tangent loss was also found to be decreased on the incorporation of La into NBT. The ac conductivity of the La-modified NBT obeyed the double power law behavior. Complex impedance spectroscopy has been carried out for better understanding of relaxation process and correlations between the microstructure–electrical properties of the materials. [Copyright &y& Elsevier]

Free standing and flexible ferroelectric ceramic-polymer composites (PVDF+ ϕ wt.% of BNBT (0.94Na 0.5 Bi 0. 5 TiO 3 -0.06BaTiO 3)) with 0–3 connectivity were synthesized by solution-casting technique. Composite nature and homogeneous distribution of ceramic filler particles in PVDF were confirmed with x-ray diffraction and scanning electron microscopic analysis. The intensity ratio of β-phase with respect to α–phase i.e., I 20.2° /I 18.4° (obtained from XRD analysis) and the fraction of electro-active beta phase i.e., F(β)% (obtained from FTIR analysis) are enhanced with increase in filler concentrations and peaked for 35 wt% of the ceramic filler. An enhancement of the % of crystallinity (calculated from XRD analysis) has been observed with increase in the filler concentrations. The increase of the fraction of β-phase has been explained on the basis of ion (negatively charged surface ion of the ferroelectric ceramic filler) -dipole (-CH 2 dipole of the polymer matrix) interactions, as evidenced from FTIR and UV-VIS absorbance spectra. Relative dielectric permittivity (dielectric constant) and ferroelectric polarization were found to be highest for the composite with 35 wt% of ferroelectric ceramic filler. Percolation theory has been successfully employed to explain the observed trend in the dielectric properties with the compositional variation. Significant enhancement in the electro active β-phase has been correlated with the improved dielectric and ferroelectric properties of the composite. Image 1 • Synthesis of ferroelectric -polymer composites with solution-casting technique. • Structural, microstructural, vibrational and dielectric properties have been studied in detailed. • Ferroelectric properties of the composite correlated to the β-phase. • Percolation theory explained the dielectric properties with the composites. [ABSTRACT FROM AUTHOR]

Polycrystalline nano BiFeO3 powders were synthesized by auto-combustion method using urea as fuel and metal nitrates (Fe(NO3)3·9H2O, Bi(NO3)3·5H2O) as oxidizers. In order to optimize the single-phase synthesis condition of BiFeO3, different fuel to oxidizer ratios have been investigated. The preliminary structural investigation using X-ray diffraction shows the samples were of single phase and crystallize in rhombohedral structure (R3c). The ferroelectric and antiferromagnetic ordering temperatures of BiFeO3 were found to be 832 °C and 364 °C respectively, from differential thermal analysis. The temperature dependent dielectric study shows an anomaly around 215 °C which corresponds to magneto-electric coupling in the material. Field-emission scanning electron micrographs show effect of fuel to oxidizer ratio on grain size evolution. The ferroelectric hysteresis loops for all the samples were measured at a frequency of 100 Hz confirming the ferroelectric nature. An evidence of magneto-electric coupling was also observed at room temperature from magneto-capacitance measurements. [ABSTRACT FROM AUTHOR]