Translational Boundaries of Antiferroelectrics as Topologically-Protected Polar Domains

Antiferroelectric materials are characterized by their antipolar dipole arrangement. Such antipolar arrangements can be disrupted by so-called translational boundaries, which separate antiferroelectric domains where the dipolar ordering is the same, but shifted by an integer number of sub-lattice units. The simplest manifestation of such translational boundaries are antiphase boundaries, where two adjacent domains are separated by half a unit cell. The antiferroelectric archetype, PbZrO3, has an unit cell that contains four dipoles, and in theory it can therefore have up to three types of translational boundaries, whereby the dipolar arrangement across the boundary is shifted by pi/2, pi or 3pi/2. Experimentally, however, we have observed “translational boundaries” with an arbitrary number of unit cells, resulting in phase shifts bigger than 2pi. These are de-facto polar domains with their own internally symmetry, polarization and electric field response. But, while they are domains, they are also, still, translational boundaries topologically constrained by their adjacent antiferroelectric domains. The dual nature of these ultra-wide translational boundaries and their functional consequences will be discussed in the talk, together with experimental evidence for their existence.