Distinct origins of electric-field-axis and polarization-axis asymmetries in ferroelectric hysteresis

Ferroelectric hysteresis asymmetry critically influences switching stability, imprint, and preferential polarization states in nonvolatile electronic devices. However, hysteresis asymmetry is generally characterized only by horizontal loop shifts, partly because conventional polarization–electric-field measurements contain an integration-constant ambiguity that prevents independent evaluation of polarization-axis asymmetry. Here, we reveal that ferroelectric hysteresis asymmetry contains two physically distinct components by using pyroelectric hysteresis measurements that avoid this offset ambiguity. Congruent LiTaO 3 exhibits a pronounced electric-field-axis shift associated with defect-related internal bias, whereas near-stoichiometric LiTaO 3 exhibits pronounced polarization-axis asymmetry despite a small internal bias. Combined cycling experiments, sweep-field dependence, Rayleigh analysis, and piezoresponse force microscopy imaging identify domain-wall pinning and an unswitched polarization component as the origin of the polarization-axis asymmetry. In contrast, the electric-field-axis shift is governed primarily by a reconfigurable defect-related internal-bias state. These results demonstrate that ferroelectric hysteresis asymmetry should not be characterized solely by a horizontal loop-shift parameter and establish a framework for decoupling internal-bias and pinned-domain effects in ferroelectrics. The findings provide materials-design principles for improving switching reliability, imprint control, and polarization-state engineering in defect-engineered ferroelectrics.