Antiferroelectricity in Oxides: A Reexamination

The fundamental physics of antiferroelectric oxides and their properties are reviewed. First, the difficulties in formulating a precise definition of antiferroelectricity are discussed, drawing on previous discussion in the literature. We arrive at the following definition: an antiferroelectric is the same as a ferroelectric in that its structure is obtained through distortion of a nonpolar high-symmetry reference phase; for ferroelectrics, the distortion is polar, while for antiferroelectrics it is nonpolar. However, not all nonpolar phases thus obtained are antiferroelectric: in addition, there must be an alternative low-energy ferroelectric phase obtained by a polar distortion of the same high-symmetry reference structure, and an applied electric field must induce a first-order transition from the antiferroelectric phase to this ferroelectric phase, producing a characteristic P–E double hysteresis loop. For analysis of the characteristic properties of antiferroelectrics, we use Landau theory functionals. The microscopic origins of the macroscopic behavior are examined. This is fairly straightforward for systems with clearly defined reorientable local-dipolar entities, such as antiferroelectric liquid crystals and hydrogen-bonded antiferroelecrics, and these systems are not discussed in detail in this chapter. The main focus is on the subtler case of antiferroelectric oxides, for which models based on symmetry-adapted lattice modes prove to be useful. Specific examples of antiferroelectric oxides are presented with available first-principles results and discussion of the role of compositional tuning in producing antiferroelectricity, and the nature of the electric-field-induced ferroelectric phases. In thin films and superlattices, additional tuning is possible through the effects of strain and finite size. This chapter concludes with some remarks on materials design, including the optimization of properties relevant to technological applications of antiferroelectrics.