Creep behavior of perovskite-type oxides Ba0.5Sr0.5(Co0.8Fe0.2)1−xZrxO3−δ

Abstract

Compressive creep tests have been performed on perovskite-type oxides Ba0.5Sr0.5(Co0.8Fe0.2)1–xZrxO3−δ (BSCF-Z100·x), where x=0.01, 0.03, 0.05 and 0.1, for the use as oxygen transport membrane, in air at 800–950°C and at nominal stresses of 30MPa and 63MPa. X-ray diffraction and microstructural observations support a solid solubility limit of ZrO2 between 0.03<x<0.05. Evidence is found for the formation of (Ba,Sr)ZrO3 secondary phases in grain boundaries at compositions beyond this limit. Zr substitution of (Co,Fe) in BSCF is found to suppress grain growth significantly, which is attributed to a solute and/or particle drag (Zener pinning) mechanism. Observed activation energies and stress exponents point to diffusional creep as the predominant mechanism for creep in BSCF-Z100·x ceramics, at T≥850°C. This is further supported by the fact that the grain-size-normalized steady-state creep rate varies little for the different BSCF-Z100·x compositions. It was confirmed that Zr substitution does not significantly affect the thermal hysteresis of the creep behavior as observed for pure BSCF.