Phase relation in the BaO–ZrO2–YO1.5 system: Presence of separate BaZrO3 phases and complexity in phase formation

In order to estimate the phase stability and homogeneous range of BaZrO3, which is expected as a candidate electrolyte material for intermediate temperature solid oxide fuel cell, the phase relation in the BaO–ZrO2–YO1.5 systems has been examined at a typical processing temperature of 1600 °C. The stable existence of two cubic phases of BaZrO3, termed as BZ(I) and BZ(II), with different dopant concentration is observed above 1400 °C in the present study. The latter is of long-range ordered supercell with a wide range of solid solution between Ba3Zr2YO8.5 and Ba9Zr4Y8O29. Also observed is the presence of liquid phase at higher BaO concentration region above the ternary eutectic temperature that is estimated to be around 1300 °C, giving enormous effects to sintering process when Y3+ is overdoped beyond the solubility limit. From the present results, the pseudo-ternary phase diagram of BaO–ZrO2–YO1.5 of the isothermal section at 1600 °C is proposed.

► We propose a complete set of phase diagram for the BaO–ZrO2–YO1.5 system at 1600°C. ► We found a new ordered nonstoichiometric phase of Ba9Zr6–2xY3 + 5xO(51 + 7x)/2 (x = 0–1). ► We propose the new low Y-solubility limit of x = 0.15 for the BaZr1–xYxO3–δ phase. ► We found liquid phase present at processing temperature solidify in complex phases.