Symmetry-breaking triggered by atomic tungsten for largely enhanced piezoelectric response in hexagonal boron nitride

The breakdown of crystal symmetry leads to the emergence of lattice distortions, which play an essential role in the piezoelectric properties. However, strategies aimed at symmetry breaking are mainly restricted to traditional crystallographic considerations, such as doping or control synthesis of particular material phases, which greatly limited the scope of piezoelectric investigations. Here, we report for the first time a "heavy ball-pressed-cloth" strategy can be applied to a wide range of materials with significantly enhanced piezoelectric response. For instance, the anchoring of single-atom tungsten (W) into hexagonal boron nitride (h-BN) nanosheets can greatly enhance the piezoelectric response, by approximately 12-fold that of the parent h-BN nanosheets even at a rather small W loading of 0.34 at.%. The boosted piezoelectric is ascribed to the fact that the 5d metal W can act as a "bolt" in causing significant lattice distortions when anchoring into two-dimensional (2D) lattice, thus introducing a strikingly large out-of-plane polarization. Our findings provide insights into the lattice dynamics related with single-atom metals, and demonstrate a universal experimental technique that would be useful in the management about the piezoelectric properties.