Origin of giant spin-lattice coupling and the suppression of ferroelectricity in EuTiO₃ from first principles

We elucidate the microscopic mechanism that causes a suppression of ferroelectricity and an enhancement of octahedral rotations in EuTiO₃ from first principles. We find that the hybridization of the rare-earth Eu 4f states with the B-site Ti cation drives the system away from ferroelectricity. We also show that the magnetic order dependence of this hybridization is the dominant source of spin-phonon coupling in this material. Our results underline the importance of rare-earth f electrons on the lattice dynamics and stability of these transition metal oxides.