Ferro- and Antiferroelectricity: Order/Disorder versus Displacive, N.S.Dalal, A.Bussmann-Holder

Solid-state systems are frequently classified according to their physical, structural or chemical properties. Such schemes are extremely helpful since properties related to any such classification are typically known and facilitate identifying solids with special material classes. The best-known examples of these schemes are conductivity or resistivitymeasurements bymeans of whichmetals are easily distinguishable from insulators. However, frequently clear-cut decisions between material classes are not possible, since anisotropy, chemical composition, binding forces and local effects wash out distinct properties and lead to competition or coexistence. Such unresolved situations are especially typical for transitionmetal oxides that exhibit a variety of ground-state properties in a fascinating way. Here chemical substitution, doping, pressure or temperature effects easily influence the physical properties and may, for instance, induce metal/insulator, antiferromagnet/ ferromagnet, insulator/superconductor transitions. This situation is analogous to perovskite ferroelectrics and hydrogen-bonded ferroelectrics, where ferroelectric/antiferroelectric transitions occur with chemical substitutions of one of the constituent sublattices. In addition, glass-like states (dipolar glasses) are observed and relaxor ferroelectricity with a large potential for applicationfrequently occurs.