Symmetry-Guided Functional Pathways of Intercalation-Free Rhombohedral ( R3 ) Hafnia Derived from the Fluorite Phase for Low-Coercive Ferroelectric Memory

Rhombohedral hafnia-based ferroelectrics promise low-coercive, scalable nonvolatile memories, yet their realization has traditionally relied on complex cation intercalation or external stress. Here, we demonstrate a possible intrinsic route to the rhombohedral (R3) phase in Hf1-xZrxO₂ through symmetry breaking of the parent fluorite lattice. First-principles calculations under R3 symmetry-constrained equation-of-state conditions show that the 12-atom fluorite-derived configuration, at equiatomic composition (x = 0.5), stabilizes an intrinsically polar R3 ground state with spontaneous polarization Ps = 44.9 μC cm⁻², dielectric permittivity εr = 51.3, an ultralow switching barrier of 27.8 meV f.u.-1, and a coercive field of 0.46 MV cm⁻¹. Distinct from orthorhombic Pca21, the R3 structure shows nonmonotonic dielectric behavior, revealing a symmetry-renormalized polarization mechanism beyond conventional Vegard-type ferroelectricity. Moreover, the R3 phase stabilizes at reduced thickness, with low built-in potential at proper electrodes preserving its low coercive field. Experiments using fast Fourier transform and geometric-phase analysis validate these predictions, and R3-phase-dominant Hf1-xZrxO₂ capacitors exhibit comparably low coercive fields (0.65 MV cm⁻¹) and enhanced dielectric permittivity εr = 39.1.