Low-symmetry phases and loss of relaxation in nanosized lead scandium niobate

Using a combination of experimental and theoretical techniques, we reveal that lead scandium niobate (PSN) nanograins exhibit a critical size of ≈65 nm below which the ground state is not anymore rhombohedral but rather monoclinic for chemically disordered systems. A triclinic ground state is further found for chemically ordered nanosized PSN. Such changes in symmetry are associated with a change in the polarization's direction, as well as, with an enhancement of the polarization's magnitude and a vanishing of relaxation. First-principles-based calculations point toward an internal electric field and mechanical constraints for the origins of these unexpected features.