Synthesis and characterization of bismuth vanadate electrolyte material with aluminium doping for SOFC application

Solid electrolytes are the most important and indispensable part of a solid oxide fuel cell (SOFC) where hydrogen is used as one of the fuels to obtain electricity. Bismuth vanadate used as an electrolyte in SOFC when doped with different divalent and trivalent metal ions provides good ionic conductivity. Higher temperature γ-phase (600 - 700 ^{{ring operator}} C) of bismuth vanadate which exhibits a higher ionic conductivity can be stabilized at room temperature by various substitutions such as copper, aluminium and titanium and is denoted as BIMEVOX. In the present study a new series of Bi₄ V_{2 - x} Al_x O_{11 - δ}(0 ≤ x ≤ 0.4) samples were prepared by taking an appropriate amount of constituent oxides. The sintered pellets were characterized by a scanning electron microscope (SEM) and an X-ray diffraction (XRD) technique. An AC conductivity measurement of all the samples in the temperature range of 200 - 700 ^{{ring operator}} C was done. The conductivity measurement data exhibited a higher ionic conductivity for the sample doped with aluminium for the composition x = 0.2 as compared with other doped samples of the same series. Since the grain size and its phase distribution influence the conductivity to a great extent, the sintering parameter for the sample x = 0.2 was varied between 750 and 825 ^{{ring operator}} C in an interval of 25 ^{{ring operator}} C. The details of the conductivity behaviour of these samples along with their microstructural characteristics are presented in this paper. The Arrhenius plots clearly indicate the various slope changes, which are in agreement with the phase transitions that occur in these samples. The results are discussed in the light of vacancy formation and disorder enhancement in the doped samples.