A research team led by Professor Hong Jiawang and Professor Wang Xueyun from the School of Aerospace Engineering and the State Key Laboratory of Environment Characteristics and Effects for Near-space at the Beijing Institute of Technology (BIT), in collaboration with Professor Nie Yuefeng's team at Nanjing University, has revealed the mechanism of nonreciprocal bending in ferroelectric membranes.

The findings were published online in the journal Advanced Materials on Oct 14 under the title "Nonreciprocal Bending in Ferroelectric Membranes Driven by Flexoelectricity".

Nonreciprocity — different responses to signals traveling in two opposite directions — has drawn wide attention in optics, acoustics, and spin-wave research. However, nonreciprocity in quasi-static mechanical systems remains largely unexplored. For centrosymmetric dielectric films, bending in opposite directions is conventionally expected to produce the same mechanical response. In polar ferroelectric materials, however, bending-induced strain gradients generate flexoelectric fields, which may cooperate with or compete against the spontaneous polarization depending on the bending direction — opening the possibility of nonreciprocal bending.

Building on this idea, the BIT team studied freestanding single-crystal PbTiO3 (PTO) membranes using suspended-membrane nanoindentation. The membranes showed markedly different mechanical responses under opposite bending directions, with the effective elastic modulus differing by up to 33 percent, and their elastic recovery after bending was also clearly asymmetric. Further analysis traced the asymmetric response to ferroelectric domain switching driven by flexoelectricity.

The study extends nonreciprocity research from dynamic propagation responses to quasi-static mechanical responses and demonstrates the feasibility of tailoring ferroelectric domain structures through flexoelectricity, offering a route toward ferroelectric devices with tunable mechanical responses.