The design concept and kilohertz performance of the PD-AKN material system.

The research group of Professor Wu Haijun, led by Xi'an Jiaotong University (XJTU)'s Academician Sun Jun from the State Key Laboratory for Mechanical Behavior of Materials and Professor Ding Xiangdong from the School of Materials Science and Engineering, in collaboration with Professor Li Jingfeng's team from Tsinghua University, has published a research paper titled Ultrahigh piezoelectricity by polaron-defect complexes in the journal Science.

The joint research team constructed a dynamically reconfigurable point-defect ordering structure – namely polaron-defect (PD) complex ordering – in silver niobate (AKN)-based thin films, thereby forming the PD-AKN material system.

Under DC bias activation, the field-induced effective piezoelectric coefficient of PD-AKN reaches 7170 pm V-1 at 1 kHz, with a maximum field-induced strain of 6.2 percent. At 10 kHz, the field-induced effective piezoelectric coefficient still reaches 1,090 pm V-1, demonstrating exceptional kilohertz electromechanical response.

The core design of PD-AKN utilizes fast-hopping small electronic polarons (localized electronic states coupled with local lattice distortions) to drive defect polarization changes, thereby combining "large defect polarization" with "fast electron dynamics" to achieve a "fast and large" field-induced electromechanical response.

Unlike the long-range migration of ionic defects, this electron-mediated local reconstruction has much faster kinetics while still strongly modulating the lattice, offering a new design paradigm for reconciling response amplitude with operating frequency.

The kilohertz ultrahigh response of PD-AKN indicates that electronic states, lattice distortions, and response kinetics can be co-designed within the same material. Charged defects spatially anchor small electronic polarons, external fields regulate their dynamic reconstruction, and local charge changes are converted into macroscopic strain via lattice coupling.

This polaron-driven charge-lattice synergistic response provides a new physical foundation and material design pathway for constructing electromechanical materials with both large deformation and fast kinetics outside of traditional ferroelectric mechanisms.