Unlocking the phase evolution of the hidden non-polar to ferroelectric transition in HfO<sub>2</sub>-based bulk crystals.

Wang, Shuxian; Shen, Yihao; Yang, Xiaoyu; Nan, Pengfei; He, Yuzhou; Lu, Ning; Yu, Haohai; Ge, Binghui et al. · Nat Commun · 2025

basic_science · Level V

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Abstract

The discovery of ferroelectricity in hafnium dioxide (HfO<sub>2</sub>) thin films over the past decade has revolutionized the landscape of ferroelectrics, providing a promising candidate for next-generation ferroelectrics beyond the constraints of Moore's law. However, the underlying formation mechanism of their metastable and volatile ferroelectric phase is under debate. Herein, we successfully grow HfO<sub>2</sub>-based (Lu:Hf<sub>1-x</sub>Zr<sub>x</sub>O<sub>2</sub>) bulk crystals and gain a comprehensive understanding of the non-polar to ferroelectric phase evolution. We achieve a controllable polymorphic engineering by elucidating the synergistic modulation of co-doped Lu<sup>3+</sup> and Zr<sup>4+</sup> ions. Our investigation unveils the intricate local structural transitions involved in the formation of the ferroelectric orthorhombic Pbc2<sub>1</sub> phase from the metastable tetragonal phase. We also establish a controllable tetragonal-to-orthorhombic transformation route, effectively improving the ferroelectric phase component within bulk crystals. Our findings will advance the comprehension of ferroelectric mechanisms in fluorite-structured materials, paving the way for significant strides in developing HfO<sub>2</sub>-based nonvolatile electronic and photonic devices.