Phase engineering of relaxor ferroelectricity in van der Waals crystal

Phase engineering of two-dimensional van der Waals materials offer a rich landscape to uncover the potential ferroelectric properties. The precisely controlling phases in these reduced dimensional materials with the unique atomic arrangement are crucial. Herein, through a novel phase engineering approach, we synthesize CuInP₂(S_1-xSe_x)₆ crystal with controllable coexistence of monoclinic and trigonal phases, and experimentally realize relaxor ferroelectricity in low-dimensional materials. Composition tailoring creates an intermediate phase transition region, which facilitates the evolution of ferroelectricity into relaxor ferroelectricity and eventually superparaelectricity. The relaxor ferroelectric properties are verified by the hysteresis-free polarization switching and diffused phase transition. High-resolution transmission electron microscopy reveals that edge dislocations play a critical role in forming locally disordered polar structures. When integrated it into a memristor device, the relaxor crystal with nanodomains demonstrates an increased number of analog resistance states and lower operating voltages compared to conventional ferroelectric crystals. This work establishes a phase engineering strategy to tailor ferroelectric behavior in low-dimensional materials, offering substantial potential for future electronic applications.