Atomic-scale strain-confined ferroelectricity in fluorite hafnium dioxide

HfO ₂ -based ferroelectrics hold exceptional promise for next-generation microelectronics, offering robust ferroelectricity down to the nanoscale while maintaining compatibility with CMOS technology. However, stabilization of the ferroelectric orthorhombic phase ( o -FE) is consistently challenged by the simultaneous formation of its antiferroelectric counterpart ( o -AFE). This unresolved o -FE/ o -AFE competition, particularly under strain, is a critical factor driving undesirable device phenomena like ‘wake-up’ and ‘fatigue’. To decipher the strain-confinement effects governing o -FE stability at coherent o -phase interfaces, we have developed a bulk-crystal strategy. This approach overcomes thin-film strain complexities by leveraging larger grain sizes and simplified strain landscapes. Integrating advanced microscopy with theoretical calculations, we demonstrate that specific biaxial strain—tensile along the a -axis coupled with compressive along the b -axis—proves sufficient to stabilize the o -FE phase, while strain relaxation favors o -AFE dominance. Direct atomistic tracking reveals the mechanisms underlying the formation of the o -FE phase and the evolution pathway between o -FE and o -AFE phases. Our work establishes a unified strain-mediated mechanism for the ubiquitous phase switching between the o -FE and o -AFE phases observed in HfO ₂ -based materials, delivering a fundamental framework to design high-performance fluorite ferroelectrics. This has broad implications for advancing microelectronics and neuromorphic computing.