Piezoelectric and dielectric constants of topologically defected boron nitride nanotubes.

Boron nitride nanotubes (BNNTs) form a promising low-dimensional piezoelectric material that may be used for multifunctional energy-harvesting nanopiezoelectronic devices. The piezoelectric and dielectric constants of a single-walled BNNT are determined a molecular dynamics simulation with several Tersoff-like potential models and Born effective charges. The effect of Stone-Wales (SW) defects on the electroelastic behavior of BNNTs is considered, owing to their importance in determining the multifunctionality of BNNTs. Both solid and hollow cylinder structures are considered as equivalent continuous tubular structures that represent the BNNT in terms of electroelasticity. Direct and reverse piezoelectricity of the BNNTs are simulated by applying elastic strain and a constant electric field along the longitudinal direction of each tube, respectively. The initial polarization of the BNNTs changes, owing to the rotation of boron and nitrogen atoms. The Tersoff potential model considered herein predicts an increase in the dielectric constant with the SW defect, which is attributable to the opposite electric displacement of nitrogen and boron atoms under an electric field. It is also observed that the elastic modulus of BNNTs is degraded by the SW defect. However, the piezoelectric constants of the BNNTs either increase or decrease as the SW defect accumulates, exhibiting a strong dependency on the applied Tersoff potential model. The performance of each Tersoff potential model in describing the geometry of the SW defect and the effect of a change in polarization and electric displacement on the electroelasticity of BNNTs is discussed. The results herein offer a deep insight into the application of BNNTs to nanopiezoelectronics and a guideline to designing the optimal BNNT composition and topology for multifunctional energy-harvesting nanocomposites.