Controlled 90° domain wall motion in BaTiO₃ piezoelectric ceramics modified with acceptor ions localized near grain boundaries

The irreversible motion of non-180° ferroelectric domain walls is a predominant cause for the increased hysteretic loss in piezoelectric ceramics at elevated temperatures. In this study we designed piezoelectric ceramics modified with acceptor ions localized near grain boundaries for the purpose of suppressing the irreversible domain wall motion at elevated temperatures without diminishing the contribution from the reversible domain wall motion. Particles of undoped BaTiO₃ (BT) were coated with Mn-doped BT by a coprecipitation method and then sintered to form a Mn-modified BT ceramic. Structural and dielectric characterizations indicated that the Mn ions in the resulting ceramic were localized near grain boundaries. The measurement of the unipolar electric-field-induced strain was conducted for the Mn-modified and unmodified (pure) BT ceramics at temperatures up to 120 °C (just below the Currie temperature) to discuss the hysteretic behavior in their piezoelectric response. The results showed that the effective piezoelectric coefficient d₃₃^* of the Mn-modified BT ceramic was comparable to the unmodified BT ceramic. The hysteresis of the Mn-modified BT ceramic was retained below 40% in the whole temperature range whereas that of the unmodified BT ceramic increased significantly at elevated temperatures over 100 °C. The results in this study demonstrate that the localized Mn ions effectively pin the domain walls to suppress their irreversible motion at elevated temperatures, while the reversible motion inside the grains remains possible.