ABO3-type oxides—Their structure and properties—A bird's eye view

ABO3-type oxides form an important class of materials of great technical value in several device applications. Such oxides are known to exist with a wide range of A and B ions. Most of these oxides have the relatively simple structure of the mineral perovskite (CaTiO3). The ideal perovskite structure has a cubic unit cell. However, distortions are common and depend upon the value of the tolerance factor t given by γA + γO/√2(γB + γO). Rhombohedral structure or orthorhombic GdFeO3-type structure is found when t is less than unity. Polytypic structures are observed when t is greater than unity. Other structures such as ilmenite and pyrochlore also occur. ABO3-type oxides display a wide spectrum of physical properties of technical importance such as ferroelectricity, antiferroelectricity, piezoelectricity, insulating behaviour, semiconductivity, metallic conductivity, superconductivity, ferromagnetism, antiferromagnetism etc. The ferroelectric properties are mostly controlled by the relative sizes of the ions. The electrical and magnetic properties are mainly dependent on the electronic configuration of the ions. Dopants and substituents have a profound influence on the properties of the ABO3 oxides.