The origin of hyperferroelectricity in Li$B$O$_3$ ($B$=V, Nb, Ta, Os)

TL;DR

This study uses first-principles calculations to explore the electronic and structural origins of hyperferroelectricity in Li$B$O$_3$ compounds, revealing that short-range interactions drive hyperferroelectric instability, unlike proper ferroelectrics.

Contribution

It identifies Li$B$O$_3$ as hyperferroelectrics with a novel instability mechanism driven by short-range interactions, expanding understanding of ferroelectric materials.

Findings

Li$B$O$_3$ compounds are hyperferroelectrics with unstable longitudinal optic phonon modes.

The ferroelectric-like instability in LiOsO$_3$ is a special case of hyperferroelectricity.

Hyperferroelectric instability is driven by short-range interactions, not long-range Coulomb forces.

Abstract

The electronic and structural properties of Li$B$O$_3$ ($B$=V, Nb, Ta, Os) are investigated via first-principles methods. We show that Li$B$O$_3$ belong to the recently proposed hyperferroelectrics, i.e., they all have unstable longitudinal optic phonon modes. Especially, the ferroelectric-like instability in the metal LiOsO$_3$, whose optical dielectric constant goes to infinity, is a limiting case of hyperferroelectrics. Via an effective Hamiltonian, we further show that, in contrast to normal proper ferroelectricity, in which the ferroelectric instability usually comes from long-range coulomb interactions, the hyperferroelectric instability is due to the structure instability driven by short-range interactions. This could happen in systems with large ion size mismatches, which therefore provides a useful guidance in searching for novel hyperferroelectrics.