  Ferroelectricity in binary oxides including hafnia and zirconia have riveted
the attention of the scientific community due to highly unconventional physical
mechanisms and the potential for integration of these materials into
semiconductor workflows. Over the last decade, it has been argued that
behaviors such as wake-up phenomena and an extreme sensitivity to electrode and
processing conditions suggests that ferroelectricity in these materials is
strongly coupled with additional mechanisms, with possible candidates including
the ionic subsystem or strain. Here we argue that the properties of these
materials emerge due to the interplay between the bulk competition between
ferroelectric and structural instabilities, similar to that in classical
antiferroelectrics, coupled with non-local screening mediated by the finite
density of states at surfaces and internal interfaces. Via decoupling of
electrochemical and electrostatic controls realized via environmental and
ultra-high vacuum PFM, we show that these materials demonstrate a rich spectrum
of ferroic behaviors including partial pressure- and temperature-induced
transitions between FE and AFE behaviors. These behaviors are consistent with
an antiferroionic model and suggest novel strategies for hafnia-based device
optimization.
