Relaxor behavior in rocksalt cation-ordered material induced by (anti)ferroelectric phase competition

Relaxor ferroelectrics are characterized by dispersion of the temperature-dependent dielectric constant with frequency and enhanced electromechanical coupling. These properties arise from the dynamic polar response of correlated nanodomains that are strongly associated with atomic-scale compositional disorder, which disrupts long-range ferroelectric ordering and enables nanodomain formation. Here, we report relaxor properties originating from spontaneous low temperature phase competition in fully cation-ordered antiferroelectric PbMg_0.5W_0.5O₃ epitaxial films, including the identification of a new low-energy polar phase. Unlike prototypical relaxors, the B-site cations in coherently strained PbMg_0.5W_0.5O₃ films exhibit long-range rocksalt chemical ordering. Temperature-dependent polarization studies reveal the switching behaviors associated with the phase transitions from paraelectric to antiferroelectric to ferroelectric, and the characteristic dielectric relaxation is ascribed instead to phase competition between the polar and antipolar phases mediated by temperature and substrate clamping. This phase competition breaks long-range dipole correlation and leads to dielectric dispersion and relaxor behavior. These findings demonstrate a new paradigm for designing relaxor material properties through engineered phase competition.