Anti-Ruddlesen-Popper A4X2O, a new family of (anti-)ferroelectric and magnetoelectric multiferroic materials discovered through high-throughput computing

Ferroelectric materials are of great fundamental and applied interests. For decades, most applications have relied on ferroelectric oxide perovskites. However, the need to combine ferroelectricity with other properties such as visible light absorption or long-range magnetic order is driving the search for materials and structural classes beyond perovskites.

We show here how the search for new ferroelectrics can be accelerated using high-throughput computing and a recently built database of more than 2,000 phonons. Browsing the phonon database, we identify materials exhibiting dynamically unstable polar phonon modes, a signature of a potential ferroelectric. We focus on a new family of ferroelectric materials discovered through this high-throughput screening approach: the anti-Ruddlesden-Popper phases of formula A₄X₂O with A: a +2 alkali-earth or rare-earth element and X: a −3 anion Bi, Sb, As and P. We show that Ba₄Sb₂O is ferroelectric and in fact hyperferroelectric. The polar instability involves the movement of an anion in a cationic cage and is geometrically-driven. Introducing a magnetic element in this structure as Eu₄Sb₂O leads to a magnetoelectric multiferroic combining coupled ferroelectricity and ferromagnetism.