Complex manganese oxides with the brownmillerite structure: synthesis, crystal chemistry and properties

Structural features and methods for the synthesis of complex manganese oxides with the brownmillerite structure A₂MnB'O_5+δ (A = Ca, Sr; B' = Ga, Al) and of their derivatives are surveyed. Modern approaches to the description of crystal structures containing various types of chains of tetrahedra are considered and possible ordering patterns of these chains are discussed. The effects of the electronic structure and crystal chemical properties of the B' cations on the possibility of formation of a layered ordered structure is noted. The emphasis is placed on the anion non-stoichiometry of the brownmillerite phases and the influence of the excess oxygen (fluorine) on the structure of the compounds. A comparative analysis of properties of oxygen- and fluorine-doped brownmillerites is given. The data on the magnetic structures, transport and magnetoresistive properties of Mn-containing brownmillerites are generalised.