Antiferroelectricity with metastable polar state from the Kittel model

We have revisited the Kittel model that describes antiferroelectricity (AFE) in terms of two sublattices of spontaneous polarization with antiparallel couplings. By constructing a comprehensive phase diagram including the antiferroelectric, ferroelectric, and paraelectric phases in the parameter space, we have identified an AFE phase with stable antipolar states and metastable polar states (SAMP) when the coupling between the two sublattices is weak. We find that the metastability of the polar state in the SAMP AFE phase can lead to apparent ferroelectric behavior, depending on the measurement timescale—for example, the frequency of the applied electric field. This explains the observed ferroelectric behavior of orthorhombic hafnia, which is predicted to be antipolar from density functional theory calculations.