Abstract
The electrical conductivity, phase structure and stability of La0.99Ca0.01Nb1-xTaxO4-δ (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5, δ=0.005) a potential candidate for proton conductor for Solid Oxide Fuel Cells (SOFCs) have been investigated using AC impedance technique and in-situ X-ray powder diffraction. Partially substituting Nb with Ta elevates the phase transition temperature (from monoclinic to a tetragonal structure at high temperature) from ~520ºC for x=0 to near 800ºC for x=0.4. AC conductivity of the La0.99Ca0.01Nb1-xTaxO4-δ both in dry and wet air decreased slightly with increase of Ta content above 750ºC, while below 500ºC, it decreased one order of magnitude. It was also found that the activation energy for the total conductivity increases with increasing Ta content from 0.50 eV (x=0) to 0.58 eV (x=0.3) for the tetragonal phase, however, it decreases with increasing Ta content from 1.18 eV (x=0) to 1.08 eV (x=0.4) for the monoclinic phase. By removing the detrimental high temperature phase transition out of intermediate temperature range, partial substitution of Nb with Ta brings this class of material closer to its application in intermediate-temperature SOFCs.
