Insights into B-Site Ordering in Double Perovskite-Type Ba3Ca1+ xNb2- xO9-δ (0 ≤ x ≤ 0.45): Combined Synchrotron and Neutron Diffraction and Electrical Transport Analyses

Kalpana Singh; Wang Hay Kan; Bailey Patton; Ashfia Huq; Venkataraman Thangadurai

doi:10.1021/acs.inorgchem.7b02984

Insights into B-Site Ordering in Double Perovskite-Type Ba₃Ca_{1+ x}Nb_{2- x}O_9-δ (0 ≤ x ≤ 0.45): Combined Synchrotron and Neutron Diffraction and Electrical Transport Analyses

Inorg Chem. 2018 Mar 5;57(5):2609-2619. doi: 10.1021/acs.inorgchem.7b02984. Epub 2018 Feb 20.

Authors

Kalpana Singh¹, Wang Hay Kan², Bailey Patton¹, Ashfia Huq³, Venkataraman Thangadurai¹

Affiliations

¹ Department of Chemistry , University of Calgary , 2500 University Drive NW , Calgary , Alberta T2N 1N4 Canada.
² 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.
³ Neutron Scattering Science Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States.

PMID: 29461052
DOI: 10.1021/acs.inorgchem.7b02984

Abstract

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 CO₂ and humid conditions. For example, a simple-perovskite-type Y-doped BaCeO₃ forms BaCO₃ and ((Ce,Y)O_2-δ) under CO₂ at elevated temperature, while B-site-ordered double-perovskite-type Ba₃Ca_1.18Nb_1.82O_9-δ remains chemically stable under the same conditions. Early structural studies on Ba₃Ca_{1+ x}Nb_{2- x}O_9-δ (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 BaZrO₃, 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.