Isovalent Cation Ordering in the Polar Rhombohedral Perovskite Bi₂FeAlO₆

Abstract

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 Fe3+ and Al3+ in the polar rhombohedral R3 double perovskite structure of Bi2FeAlO6 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 BiFeO3 (R3c) and BiAlO3 (R3c), which results in reduction of symmetry to an R3 structure where the Fe3+ and Al3+ ions are ordered in a rock salt manner. However, these ions remain disordered in BiFe1−xAlxO3 (x=0.2, 0.3, 0.4) perovskites with R3c structure. The ordered compound undergoes antiferromagnetic ordering at TN≈280 K. The butterfly nature of piezoelectric displacement loop further confirms the polar nature of the cation‐ordered Bi2FeAlO6.

Dielectric Relaxation Mechanism in High-Pressure Synthesized BiCr0.5Mn0.5O3

“…Recently, there has been considerable interest in bismuth-based perovskites of the type BiMO 3 (M = transition metals), which are potential candidates for materials exhibiting multiferroic properties. [17][18][19][20] Many of the bismuth compounds [BiMO 3 (where M = Cr, Mn, Co, or Ni)] require high pressures to stabilize the perovskite structure. For example, the high-pressure phase of BiMnO 3 is a widely studied material which has a monoclinic structure (C2/c) and shows ferromagnetic behavior with T C of 100 K. 18 In fact, it has been reported that oxygen non-stoichiometry plays a crucial role in determining the structure and properties of BiMnO 3 .…”