The Ln- and Mn-Substituted Aurivillius Phases: Formation Mechanism and Physical Properties

The Aurivillius phases [Bi2O2][An-1BnO3n+1] are well-known ferroelectrics with high Curie temperatures. Recently this class of compounds attracted significant attention due to possible multiferroic and photocatalytic properties. We have investigated the possibility of the Bi→Ln and Ti→Mn substitution in the double-layered Aurivillius phases Bi3NbTiO9 and Bi3TaTiO9. In both cases substitution appeared to be limited. The Ln-substituted compounds can be obtained only for Ln=La-Gd. The Ti→Mn substitution is possible only if the substitution degree does not exceed 0.2. The formation of the double-layered Aurivillius phases has been investigated by means of the X-ray diffraction and thermal analysis. The limits of substitution have been explained on the basis of the formation mechanism. The stability of the intermediate Bi4Ti3O12-based phase appeared to be crucial for the possibility of obtaining the substituted Aurivillius phase. The temperature dependence of the dielectric and magnetic properties has been investigated. The magnetoelectric coupling is found at low temperatures.