Anomalous structural distortion - a possible origin for the waking-up of the spontaneous polarization in ferroelectric HfO2

We report that the waking-up of the spontaneous polarization (P (spon)) in ferroelectric (FE) HfO2 is related to the phase transformation driven by electric field cycling. We found an anomalous distortion, which is defined by the difference between in-plane and out-of-plane interplanar spacing induced in FE-HfO2 thin films. We further investigated and found that there is a relationship between the amount of the P (spon) that was woken up and the amount of distortion. Due to the distinctiveness of an electric field-driven phase transformation, we propose a concept of distortion as a possible origin that determines the waking-up of the P (spon) in FE-HfO2.