Large bulk piezolectric response of Van der Waals bonded quasi-2D solids

The bulk piezoelectric response of ionic solids, as measured by the piezoelectric modulus tensor d, is driven by the redistribution of a charge upon the application of stress. Hence, soft materials can generally be expected to exhibit higher piezoelectric modulus compared to stiffer systems. Motivated by the soft nature of the Van der Waals bonded quasi-2D solids, we focus our search for new piezoelectric compounds to this particular family of materials. The quasi-2D structures are identified using an automated algorithm from a pool of more than 11,000 structures reported in the Inorganic Crystal Structure Database (ICSD). The results revealed 572 materials with d_max>0.1 pC/N, out of which 192 materials have d_max greater than AlN, a material commonly used in high-frequency resonators. Interestingly, we have also found 32 compounds, including TaS₂, In₂Se₃, GeTe, and other, with moduli higher than PbTiO₃, another piezoelectric material with the bulk piezoelectric modulus among the largest known. Our results reveal the critical role of soft Van der Waals bonds between the layers as d_max often couples to a stress component (compressive or shear) orthogonal to the layers and offer guidance in selecting quasi-2D materials with high piezoelectric modulus (d).