Browsing by Author "Baral, Ashok Kumar"

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    Dielectric characteristics of fast Li ion conducting garnet-type Li5+2xLa3Nb2 xYxO12 (x = 0.25, 0.5 and 0.75)
    (Royal Society of Chemistry, 2016) Narayanan, Sumaletha; Baral, Ashok Kumar; Thangadurai, Venkataraman
    Here, we report the dielectric characteristics of Li-stuffed garnet-type Li5+2xLa3Nb2−xYxO12 (x = 0.25, 0.5 and 0.75) in the temperature range about −53 to 50 °C using AC impedance spectroscopy. All the investigated Li-stuffed garnet compounds were prepared, under the same condition, using conventional solid-state reaction at elevated temperature in air. The Nyquist plots show mainly bulk contribution to the total Li+ ion conductivity for Li5.5La3Nb1.75Y0.25O12 (Li5.5–Nb) and Li6La3Nb1.5Y0.5O12 (Li6–Nb), while both bulk and grain-boundary effects are visible in the case of Li6.5La3Nb1.25Y0.75O12 (Li6.5–Nb) phase at ∼−22 °C. Non-Debye relaxation process was observed in the modulus AC impedance plots. The dielectric loss tangent of Li5+2xLa3Nb2−xYxO12 are compared with that of the corresponding Ta analogue, Li5+2xLa3Ta2−xYxO12 and showed a decrease in peak intensity for the Nb-based garnet samples which may be attributed to a slight increase in their Li+ ion conductivity. The relative dielectric constant values were also found to be higher for the Ta member (>60 for Li5+2xLa3Ta2−xYxO12) than that of the corresponding Nb analogue (∼50 for Li5+2xLa3Nb2−xYxO12) at below room temperature. A long-range order Li+ ion migration pathway with relaxation time (τ0) 10−18–10−15 s and an activation energy of 0.59–0.40 eV was observed for the investigated Li5+2xLa3Nb2−xYxO12 garnets and is comparable to that of the corresponding Ta-based Li5+2xLa3Ta2−xYxO12 garnets.
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    Ni-Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3-Delta Anode Composites for Proton Conducting Solid Oxide Fuel Cells (H-SOFCs)
    (Canadian Center of Science and Education, 2016-09-01) Singh, Kalpana; Baral, Ashok Kumar; Thangadurai, Venkataraman
    In this paper, we report the electrochemical properties of Ni-Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3-Delta (BSCZGY) anode composites in 3% H2O-H2 for proton conducting solid oxide fuel cells (H-SOFCs). Ni-BSCZGY composites with volume ratio of 30:70, 40:60, and 50:50 were synthesised through mechanical mixing and combustion methods. In combustion method, auto-ignition step led to brown coloured ash, which was calcined at 1000 oC for 5 h to form NiO-BSCZGY powder. Screen-printing, co-firing and reduction process were used to prepare the symmetrical cell: Ni-BSCZGY/BSCZGY/Ni-BSCZGY. Ni50-BSCZGY anode exhibited the lowest polarisation resistance (Rp) of 0.8 Omega.cm2 and 1.9 Omega.cm2 at 710 oC under 3% H2O-H2, for both mechanically mixed and combustion methods, respectively.