Effect of CO₂ Exposure on the Chemical Stability and Mechanical Properties of BaZrO₃‐Ceramics

Abstract

The reactivity of BaZrO3 with CO2 has been addressed as one of the major challenges with BaZrO3-based electrolytes in proton ceramic fuel cells. Here, we present a study of the effect of CO2 exposure of BaZrO3-materials at elevated temperatures. Dense BaZr1-xYxO3-δ (x = 0, 0.05, 0.1, 0.2) and BaCe0.2Zr0.7Y0.1O2.95 ceramics were prepared by conventional sintering of powder prepared by spray pyrolysis. The Vickers indentation method was used to determine the hardness and estimate the fracture toughness of pristine materials as well as the corresponding materials exposed to CO2. Formation of BaCO3 on the surface of exposed ceramics was confirmed by X-ray diffraction and electron microcopy. The reaction resulted in formation of Ba-deficient perovskite at the exposed surface. The reaction with CO2 was most pronounced at 650 ºC compared to the other temperatures applied in the study. The reactivity was also shown to depend on the Y-content and the grain size and was most pronounced for BaZr0.9Y0.1O3-δ. The reaction with CO2 was observed to have a profound effect on the fracture toughness of the ceramics, demonstrating a depression of the mechanical stability of the materials. The results are discussed with respect to the chemical and mechanical stability of BaZrO3 materials, with particular emphasis on the composition and grain size.

134Ba diffusion in polycrystalline BaMO3 (M = Ti, Zr, Ce)

“…Loss of BaO during sintering is well documented in case of BaZrO 3 , 7 and similar dominant point defects are anticipated in the two other materials BaCeO 3 and BaTiO 3 due to the high sintering temperatures applied. Based on first principles calculations the energy of formation for the partly Schottky-type defects, reaction (3), are 3.21, 2.80 and 2.58 eV for BaCeO 3 , BaZrO 3 and BaTiO 3 , respectively.…”

“…39,40 The high processing temperature and segregation of BaO as BaCO 3 give rise to an interesting defect chemistry as discussed for BaZrO 3 with respect to materials stability and Ba-mobility. 7 Novel behavior with the implication to cation intermixing has been observed at the interface of LaAlO 3 /SrTiO 3 heterostructures such as two dimensional metallic conductivity, magnetic scattering and superconductivity. 41 …”

“…7 The BaTiO 3 ceramics were prepared by two-step sintering at 1320 • C for 1 min and 1150 • C for 15 h in air. BaCeO 3 was synthesized via solid state reaction method at 1200 • C for 5 h and sintered at 1500 • C for 10 h in air in a sacrificial powder bed consisting of BaCeO 3 and 10 wt% BaCO 3 .…”

“…[2][3][4] The high sintering temperature for these oxide materials combined with the volatility of BaO give rise to an interesting defect chemistry as discussed extensively for BaZrO 3 where Ba-deficiency is of importance for the material stability and the mobility of A-cations. 7 Cation diffusion is of fundamental interest for the understanding of properties and the chemical durability of solids. This is illustrated by the fact that cation diffusion controls sintering and grain growth during materials processing.…”

96Zr Tracer Diffusion in AZrO3 (A = Ca, Sr, Ba)

“…AZrO 3 perovskite materials are attractive due to their high proton conductivity, with potential applications in protonic ceramic fuel cells (PCFC), electrolyzers, gas sensors, and hydrogen membrane technology [1][2][3][4][5][6][7]. The majority of studies on AZrO 3 proton conductors have focused on the transport properties, but a recent study has also addressed the mobility of cations in the BaZrO 3 (BZ)-materials, revealing the challenges with solid state sintering of the ceramics and chemical instability in CO 2 at elevated temperature [8].…”