Singh Kalpana, Kan Wang Hay, Patton Bailey, Huq Ashfia, Thangadurai Venkataraman
Department of Chemistry , University of Calgary , 2500 University Drive NW , Calgary , Alberta T2N 1N4 Canada.
China Spallation Neutron Source, Institute of High Energy Physics, Chinese Academy of Sciences , Dongguan Institute of Neutron Science , Dongguan , People's Republic of China 523803.
Inorg Chem. 2018 Mar 5;57(5):2609-2619. doi: 10.1021/acs.inorgchem.7b02984. Epub 2018 Feb 20.
Perovskite-type metal oxides are being used in a wide range of technologies, including fuel cells, batteries, electrolyzers, dielectric capacitors, and sensors. One of their remarkable structural properties is cationic ordering in A or B sites, which affects electrical transport properties under different gaseous atmospheres, and chemical stability under CO and humid conditions. For example, a simple-perovskite-type Y-doped BaCeO forms BaCO and ((Ce,Y)O) under CO at elevated temperature, while B-site-ordered double-perovskite-type BaCaNbO remains chemically stable under the same conditions. Early structural studies on BaCaNbO (BCN) showed that the B-site ordering (1:1) is sensitive to the Ca content. However, ambiguity rises, as 1:2 B-site ordering was not observed in the parent and doped analogues when x was varied, which motivated us to revisit the complex oxides BCN ( x = 0-0.45) to determine the atomic structure by a mean of combined synchrotron X-ray and neutron diffraction methods. Surprisingly, the B-site ordering increases with increasing Ca/Nb mixing in the B-sites in BCN. In addition, the electrical conductivity of BCN was found to be the highest at x = ∼0.18, and it decreased as the Ca/Nb ratio further increased in BCN. Such a result was very similar to that for the Y-doped BaZrO, where the mobility of proton carriers was found to decrease as the dopant (Y) increased. A higher Ca/Nb ratio also promotes the growth of grain size, as Ca ions could serve as a sintering aid, improving the structural integrity.
钙钛矿型金属氧化物正被广泛应用于多种技术领域，包括燃料电池、电池、电解槽、介电电容器和传感器。它们显著的结构特性之一是A位或B位的阳离子有序排列，这会影响不同气体氛围下的电输运性能以及CO和潮湿条件下的化学稳定性。例如，简单钙钛矿型的Y掺杂BaCeO在高温下于CO气氛中会形成BaCO和((Ce,Y)O)，而B位有序的双钙钛矿型BaCaNbO在相同条件下保持化学稳定。早期对BaCaNbO（BCN）的结构研究表明，B位有序排列（1:1）对Ca含量敏感。然而，当改变x时，在母体和掺杂类似物中未观察到1:2的B位有序排列，这引发了歧义，促使我们重新研究复合氧化物BCN（x = 0 - 0.45），通过同步加速器X射线和中子衍射方法相结合来确定其原子结构。令人惊讶的是，在BCN中，B位有序排列随着B位中Ca/Nb混合比例的增加而增加。此外，发现BCN的电导率在x = ∼0.18时最高，随着BCN中Ca/Nb比例进一步增加而降低。这一结果与Y掺杂BaZrO的情况非常相似，在Y掺杂BaZrO中，质子载流子的迁移率随着掺杂剂（Y）的增加而降低。较高的Ca/Nb比例也促进了晶粒尺寸的生长，因为Ca离子可以作为烧结助剂，改善结构完整性。
