Nano-architected GaN spinodoid metamaterials with tailorable anisotropic piezoelectric properties

Piezoelectric properties of nanomaterials are often constrained by their intrinsic crystallographic structures. Inspired by spinodal phase separation, this study develops gallium nitride (GaN) spinodoid metamaterials with enhanced and anisotropic piezoelectric properties. Molecular dynamics simulations reveal that these metamaterials exhibit significantly improved piezoelectric stress and strain constants (e.g., d₃₃ enhanced by up to 12 times) and increased piezoelectric anisotropy (e.g., d₃₁ ≠ d₃₂) compared to bulk GaN. These enhancements in piezoelectric performance are strongly affected by their underlying nano-architecture, which is governed by the evolutionary time during spinodal decomposition. Due to the asymmetric topology designs, GaN spinodoid metamaterials can possess more independent non-zero piezoelectric stress/strain constants as well as elastic constants compared to the bulk piezoelectric GaN. Relative density is found to further modulate the piezoelectric properties and anisotropy of the nano-architected piezoelectric materials through the contribution of surface effects and tuning the surface-to-volume ratio. This work underscores the potential of topology engineering to overcome crystallographic constraints in piezoelectric nanomaterials, opening avenues for their applications in nano-energy harvesters and three-dimensional pressure mapping/sensing nano-devices.