Giant electric-field-induced strain associated with defect dipoles in Fe-doped barium titanate single crystals activated by an electric field

Aged 1 mol% Fe-doped BaTiO₃ (Fe-BTO) single crystals are activated by an alternating current (AC) electric field, leading to a remarkable electric-field-induced strain close to 1%. The mechanism of this giant electric-field-induced strain behavior is investigated. In unaged Fe-BTO, the polarization–electric field (P–E) hysteresis loop exhibits a typical single loop, which transforms into a double-pinched hysteresis loop after aging. The strain–electric field (S–E) hysteresis loop reveals a dramatic increase in strain from 0.4% to 0.9% at 3 kV mm⁻¹ after the aging. Unlike conventional thermal aging, the AC-field-activated aging process takes <1 hour, promoting domain switching and directional alignment of defect dipoles formed by Fe³⁺ dopants and oxygen vacancies. These aligned defect dipoles pin spontaneous polarization at low field, and once a threshold field is exceeded, they trigger abrupt 90° domain switching, producing the giant strain. Phase-field modeling confirms that dipole alignment, rather than defect migration, biases domain switching, facilitating this giant electric-field-induced strain response. The electric field-induced giant strain in aged Fe-BTO single crystals can be used for low frequency actuator applications.