Xia Hong http://orcid.org/0000-0002-7873-5774
Date of this Version
Published in Nature Materials 22 (September 2023), pp. 1049–1050.
Piezoresponse microscopy and spectroscopy reveal the inextricable role of surface electrochemistry in stabilizing and controlling ferroelectricity in doped hafnia.
Doped hafnia (HfO2), a relatively new member of the ferroelectric family, has challenged in many ways our conventional perception of ferroelectric oxides. It possesses extremely localized electric dipoles that are independently switchable,1 making it immune to finite size effects — the loss of long-range dipole order in ferroic materials due to size scaling. While polycrystalline grains and microstructures can yield lower polarization and poorer cycling behavior in canonical ferroelectrics such as Pb(Zr,Ti)O3 and BaTiO3, in hafnia, confined dimensions often seem to be the key to success,2 with ferroelectricity substantially compromised in films thicker than 20 nm (ref. 3). The recent report of a record high polarization in epitaxial yttrium-doped HfO2 thin films4 further escalates the debate about whether the intrinsic structural constraint competes with or complements extrinsic mechanisms such as oxygen vacancy migration5 in anchoring ferroelectric instability in this material. Now, writing in Nature Materials,6 Kelley and colleagues add a previously overlooked element into the puzzle, discussing whether surface electrochemistry could be the missing link in understanding ferroelectric hafnia.