Structural instability of cubic perovskite BaxSrxSr1-xCo1-yFeyO3-δ
Structural instability of cubic perovskite BaxSrxSr1-xCo1-yFeyO3-δ
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DOI：
10.1016/j.ssi.2007.11.031
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发表时间：
2008-02-15
影响因子：
3.2
通讯作者：
Grande, Tor
中科院分区：
文献类型：
--
作者：
Svarcova, Silvie;Wiik, Kjell;Grande, Tor
立方钙钛矿BaxSr1-xCo0.8Fe0.2O3Delta(BSCF)是最有前途的中温固体氧化物燃料电池透氧膜材料和高性能阴极材料之一。在这里，我们发现立方的BSCF在空气中中温变得不稳定，冷却后逐渐转变为六方钙钛矿。在850-900℃下观察到立方和六方BSCF晶型共存，并且随着温度的降低，六方晶型的数量增加，立方晶型的数量减少。推测这两种共存相的化学成分不同，但缓慢的阳离子扩散阻碍了向六方晶型的完全转变。由于动力学的迟缓，通常的冷却速度会导致亚稳定的立方BSCF，但随着时间的推移，向稳定的六角形多晶型的转变可能不利于加入BSCF的应用。我们证明了BSCF的立方晶型到六角晶型的转变可以通过Goldschmidt容差因子来合理化，并相应地通过适当的取代来抑制。(C)2007 Elsevier B.V.保留所有权利。
Cubic perovskites BaxSr1-xCo0.8Fe0.2O3-delta (BSCF) are among the most promising oxygen permeable membrane materials and high-performance cathode materials for intermediate temperature solid oxide fuel cells. Here, we show that cubic BSCF becomes unstable in air at intermediate temperatures and gradually transforms to a hexagonal perovskite on cooling. Cubic and hexagonal BSCF polymorphs were observed to coexist below 850-900 degrees C, and the amount of the hexagonal polymorph was shown to increase at the expense of the cubic polymorph with decreasing temperature. Different chemical composition of the two coexisting phases was inferred, but a complete transformation to the hexagonal polymorph was hindered by slow cation diffusion. Due to the sluggish kinetics, usual cooling rates lead to the meta-stable cubic BSCF, but over time the transition to the stable hexagonal polymorph may be detrimental to applications incorporating BSCF. We show that the transformation of the cubic to hexagonal polymorph of BSCF can be rationalized by the Goldschmidt tolerance factor and accordingly suppressed by appropriate substitutions. (C) 2007 Elsevier B.V. All rights reserved.