A2BBO6

A2BBO6 is used to denote a family of double perovskite oxides with the general formula A2BB'O6, where A is a larger cation (such as Sr2+, Ba2+, or Ca2+), and B and B' are different transition metal cations that occupy alternating octahedral sites in the perovskite lattice. In this structure, oxygen atoms form octahedra around the B and B' cations, while A-site cations reside in larger, 12-coordinate voids. When B and B' cations order in a rock-salt pattern, the material adopts a doubled unit cell and exhibits properties distinct from simple ABO3 perovskites.

Structure and composition: A2BB'O6 oxides crystallize in a variety of space groups, with distortions and tilts of the BO6 and B'O6 octahedra influenced by ionic radii and valence states. The degree of B/B' ordering, as well as anti-site defects where B and B' swap positions, strongly affects magnetic and electronic behavior.

Synthesis and processing: Common synthesis routes include solid-state reaction at high temperatures, typically in the range of 900–1300°C, under controlled oxygen partial pressure to achieve the desired stoichiometry. Other methods, such as sol-gel processing, combustion synthesis, and thin-film deposition techniques (for example, pulsed laser deposition), are used to tune microstructure and properties.

Properties and applications: The physical properties of A2BB'O6 compounds depend on the chosen B and B' cations. They can exhibit ferrimagnetism or ferromagnetism, varying electronic conductivity from insulating to metallic, and sometimes magnetoresistance or spin-polarized transport. Anti-site disorder can reduce magnetic ordering and transport effects. These materials are studied for spintronic applications, magnetic sensors, and functional oxide devices.

Examples and significance: Notable members include Sr2FeMoO6 and related Sr-, Ba-, and Ca-based compounds. Research continues to explore how cation choice and synthesis conditions tailor performance for advanced technologies.