Sintering Studies on 20 mol% Yttrium-Doped Barium Cerate

Abstract

Acceptor‐doped barium cerate perovskite oxides act as high temperature proton conducting ceramics, which can be utilized in solid oxide fuel cells, hydrogen separation membranes, and other electrochemical devices. One of the major issues in their fabrication is the formation of second phases during sintering of these perovskite oxides. In this work, the formation of a second phase is investigated with an aim to understand its influence on the properties of the parent perovskite oxide and also the necessity for its removal. BaCe0.8Y0.2O3−δ (BCY20) was synthesized via a polymeric sol–gel method and characterized by X‐ray diffraction, scanning electron microscopy, and micro‐Raman spectroscopy. Formation of the second phase on the surface of the sintered pellets (sintering temperature >1250°C for 24 h) was identified to be yttria‐doped ceria (Y0.2Ce0.8O1.9). A mechanism for the formation of the second phase is proposed. The formation of second phase was prevented by sintering the pellets in a powder bath of the same composition as the parent perovskite oxide. From impedance spectroscopy measurements of pellets sintered with and without the powder bath, it was found that the second phase (in the pellet sintered without powder bath) has a negative effect on the bulk ionic conductivity of the pellet.

Fundamentals of Synthesis, Sintering Issues, and Chemical Stability of BaZr0.1Ce0.7Y0.1Yb0.1O3-δProton Conducting Electrolyte for SOFCs

“…However, some Ba loss and structural disintegration have been previously reported for barium cerate based oxides under these high temperature sintering conditions. 13,14 This results in loss of perovskite structure and low density of sintered samples. 13,14 Different approaches have been investigated to overcome sintering issues of BZCYYb material and lower the sintering temperature which include two-step sintering, 15 adjusting BZCYYb powder properties by using different synthesis method other than conventional solid state reaction (SSR) method, 16 or using 1 wt.% NiO as a sintering aid.…”

“…13,14 This results in loss of perovskite structure and low density of sintered samples. 13,14 Different approaches have been investigated to overcome sintering issues of BZCYYb material and lower the sintering temperature which include two-step sintering, 15 adjusting BZCYYb powder properties by using different synthesis method other than conventional solid state reaction (SSR) method, 16 or using 1 wt.% NiO as a sintering aid. 8 On the other hand, current data in literature 7,8,[15][16][17] have not provided understandings for observed variation in BZCYYb sintering issues and there is still a lack of fundamental study on chemical interactions during sintering process of this material.…”

“…6 Recently, BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ (BZCYYb) has received huge interest as a promising proton conducting electrolyte material for SOFCs. 4,[6][7][8][9][10][11][12][13][14][15][16] BZCYYb, which is a barium zirconate-cerate based oxide that is co-doped with Y and Yb, was first reported by Yang et al 7 as a promising electrolyte material with very high proton conductivity. This material has ionic conductivity of ∼0.06 Scm −1 at 700 • C in humidified O 2 atmosphere, and it is reported to show higher ionic conductivity values at temperatures below 750…”

“…18 However, these reports are in contradiction with poor chemical stability previously reported for BaCe 0.9-x Zr x Y 0.1 O 3-δ with low contents of Zr dopant (<0.3) under CO 2 and H 2 S contaminated atmospheres. [1][2][3]13,14 Therefore, lack of sufficient data in literature for chemical stability of BZCYYb material under different contaminated atmospheres brings the need for further studies on behavior of this material when exposed to contamination.…”

“…z E-mail: zhcheng@fiu.edu issues have been previously reported for barium-cerate materials containing low contents of Zr. 13,14 BZCYYb usually needs very high sintering temperatures (>1500…”