Ultralow barrier sliding ferroelectricity in CdAl₂S₄ with large out-of-plane polarization

Two-dimensional sliding ferroelectrics combining large out-of-plane polarization with low switching barriers are crucial for next-generation nanoscale devices. Here we predict robust sliding ferroelectricity in CdAl₂S₄ bilayers and multilayers using first-principles calculations. The CdAl₂S₄ bilayer exhibits a spontaneous polarization of 1.87 pC/m with an ultralow energy barrier of only 16.4 meV/f.u.—among the lowest reported for MA₂Z₄-family ferroelectrics. Remarkably, the polarization scales superlinearly with layer number, reaching ∼10 pC/m in six-layer structures while maintaining a moderate barrier of ∼82 meV/f.u.. We attribute this favorable behavior to the large ionic radius of Cd, which maintains wide interlayer spacing, and the high electronegativity contrast between Al and S, which enhances ionic charge transfer. This work establishes Cd-based 2D materials as a viable platform for sliding ferroelectrics and opens pathways for applications in ferroelectric field-effect transistors and tunnel junctions. © 2026 Elsevier B.V.