Role of BaZrO3 Phase on Microstructure and Ionic Conductivity of 8YSZ

The effect of BaO insertion on the ionic conductivity of 8 mol.% yttria-stabilized zirconia (8YSZ) was investigated using electrochemical impedance spectroscopy with a frequency response analyzer in the frequency range of 100 mHz-13 MHz and the temperature range of 300-800 degrees C. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis indicated that while the BaO could be dissolved in the zirconia at 1 wt.%, it did not dissolve in the zirconia above 1 wt.% (5, 10, and 15 wt.%). Furthermore, it led to forming of BaZrO3 secondary phases at the 8YSZ's grain boundaries when the BaO was doped to 8YSZ at the amounts of more than 1 wt.%. This BaZrO3 secondary phase reduced the grain size of 8YSZ from 4.48 to 0.71 mu m after sintering at 1400 degrees C for 50 h. Rietveld analysis showed that the lattice parameter of ZrO2 decreased from 5.138 to 5.130 angstrom and that of BaZrO3 decreased from 4.189 to 4.181 angstrom at a content of 15 wt.% BaO. The impedance spectroscopy results showed that zirconia's grain interior conductivity at 400 degrees C was increased from 1.17 x 10(-4) to 1.56 x 10(-4) S/cm by 5 wt.% BaO addition, and the grain boundary conductivity at 400 degrees C was also enhanced from 7.21 x 10(-6) to 4.90 x 10(-5) S/cm by 1 wt.% BaO addition. Additionally, the grain interior activation energy of 8YSZ was reduced from 1.15 to 0.97 eV by 5 wt.% BaO addition and grain boundary activation energy from 1.50 to 1.17 eV by 1 wt.% BaO addition. The most significant outcome of this study is that the grain interior and grain boundary conductivity of 8YSZ was increased by 33% and 47%, respectively, at low temperatures (400 degrees C) with the addition of BaO. In conclusion, the present study displayed that BaO addition to 8YSZ improved the ionic conductivity and might be used as a solid electrolyte material in SOFCs.