Nature Communications, Published online: 07 September 2026; doi:10.1038/s41467-026-77566-1 The authors demonstrate the synthesis of a metastable SmO2/Sm2O3 mosaic-like lateral. heterostructure using molten eutectic salt. This structural asymmetry induces an intrinsic built-in dipole, a nonlinear optical response, and room temperature interface ferroelectric polarization.