Grain Boundary Unlocks Ferroelectric Phase Regulation
Ferroelectrics with intrinsic electric polarization are indispensable for non-volatile storage and computing-in-memory chips. However, conventional perovskite ferroelectrics suffer from size effects that degrade functional properties at reduced dimensions, limiting nanoscale applications. Fluorite-based ferroelectrics, such as HfO2 and ZrO2, maintain ferroelectricity in nanocrystalline films and are compatible with Si-based processes, but their ferroelectricity relies on a metastable orthorhombic (O) phase that is thermodynamically unstable at room temperature, leading to wake-up effects, fatigue, and reduced reliability. Previous stabilization strategies (stress, doping, oxygen vacancies) lack atomic-level verification or depend on specific processing conditions. This highlight discusses a recent Nature Materials study by Wang et al. that demonstrates grain boundary (GB) chemical engineering as a new paradigm. Using a La0.67Sr0.33MnO3 (LSMO) buffer layer, they achieved stable O-phase ZrO2 films. Atomic-scale HAADF and EELS revealed ordered GBs with selective segregation of La, Sr, and Mn, forming chemically ordered heterostructures. First-principles calculations showed that the ordered eg/t2g orbital arrangement of Mn3+/Mn4+ at GBs softens phonon modes by regulating Zr–O bond strength, stabilizing the ferroelectric phase. This work establishes GBs as independent functional units, offering a universal approach for designing highly stable metastable functional materials.