Figure 5: Illustration of effects of nanopores on the polarization of a non-piezoelectric material under uniform stress.
From: Anomalous piezoelectricity in two-dimensional graphene nitride nanosheets
(a) A non-piezoelectric material with no pores exhibits no piezoelectric response; (b) with circular (centrosymmetric) pores, local polarization is non-zero while net polarization remains zero, and overall there is no apparent piezoelectric response; (c) with triangular (non-centrosymmetric) pores, a non-zero local and net polarization exist and the material possesses an apparent piezoelectricity.
