Atomic‐Scale Strain‐Confined Ferroelectricity in Fluorite Hafnium Dioxide

ABSTRACT 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 anisotropic‐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.