A modern perspective on antiferroelectrics.

Antiferroelectrics attract attention due to their unusual physical characteristics, chief among which is the double hysteresis loop that separates their antipolar ground state from the voltage-induced polar phase. This behaviour is useful for energy storage and promising for electrocaloric cooling and other applications. However, the defining features of antiferroelectrics (antipolar ground state and double hysteresis loops) are increasingly challenged: materials with non-collinear and/or hybrid polar-antipolar order have been discovered, and double hysteresis has been realized in materials without a conventional antipolar ground state. These developments add to the already intense interest in the fundamental and practical aspects of antiferroelectrics and call for a fresh look at antiferroelectricity. In this Perspective, we revise the definition of antiferroelectricity, discuss material systems with new antipolar orders and/or engineered double hysteresis, and reflect on emergent properties and theoretical approaches.