Exploring the Structure/Property Nexus in Perovskite and Pyrochlore Oxides

Perovskites comprise a very large family of materials with many important applications in areas such as dielectrics, superconductivity and photovoltaics among very many others. From a structural chemical perspective the basic perovskite, formulated as ABO3, is the parent of a large variety of structure types obtained by substitutions on both the A and B sites, crystallographic ordering on these sites, intergrowth with other structure types and significant levels of vacancies on both the A and O sites. In fact about 80% of the stable chemical elements can be accommodated within the perovskite and perovskite derived structures providing many opportunities for chemical manipulations which drive changes in physical properties. Selected examples will be given involving intergrowth materials, the Ruddlesden-Popper phases (for which a strong connection to B.E. Warren exists), so called double perovskites with cation ordering on the B - site and materials with high vacancy levels on the O site. Pyrochlore oxides, A2B2O7, are a smaller family of materials but have been studied intensively over the past several years due to a singular feature of the structure which is that both the A and B site ions reside on a sublattice consisting of corner-sharing tetrahedra which provides the condition for geometric magnetic frustration leading to an ever expanding array of exotic magnetic ground states. A discussion of the first oxide of this type to be discovered, namely Y2Mo2O7, will be presented.