Isovalent Cation Ordering in the Polar Rhombohedral Perovskite Bi 2 FeAlO 6

Ordering of cations in different structural types occurs when there is a significant difference in the oxidation states and ionic radii of the ions involved. Herein we report an unusual ordering of isovalent cations Fe 3+ and Al 3+ in the polar rhombohedral R 3 double perovskite structure of Bi 2 FeAlO 6 synthesized at high‐pressure (6 GPa) and high‐temperature (1000 °C). This ordered structure is derived from the 1:1 combination of the polar oxides BiFeO 3 ( R 3 c ) and BiAlO 3 ( R 3c), which results in reduction of symmetry to an R 3 structure where the Fe 3+ and Al 3+ ions are ordered in a rock salt manner. However, these ions remain disordered in BiFe 1− x Al x O 3 ( x =0.2, 0.3, 0.4) perovskites with R 3 c structure. The ordered compound undergoes antiferromagnetic ordering at T N ≈280 K. The butterfly nature of piezoelectric displacement loop further confirms the polar nature of the cation‐ordered Bi 2 FeAlO 6 .