Unlocking the phase evolution of the hidden non-polar to ferroelectric transition in HfO2-based bulk crystals
Shuxian Wang, Yihao Shen, Xiaoyu Yang, Pengfei Nan, Y.‐L. He, Ning Lü, Haohai Yu, Binghui Ge, Shujun Zhang, Huaijin Zhang
Abstract
The discovery of ferroelectricity in hafnium dioxide (HfO2) 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 HfO2-based (Lu:Hf1−xZrxO2) 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 Lu3+ and Zr4+ ions. Our investigation unveils the intricate local structural transitions involved in the formation of the ferroelectric orthorhombic Pbc21 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 HfO2-based nonvolatile electronic and photonic devices. The underlying formation mechanism and evolution of the ferroelectric phase in hafnium dioxide-based crystals is under debate. Here, the authors characterize the phase transitions and reveal the accompanying atomic movements in a co-doped crystal.