Effect of number of layers upon piezoelectric behaviour of multi-walled boron nitride nanotubes

In this effort, we examined the piezoelectric properties of the multi-walled boron nitride nanotubes (BNNTs), and the influence of the tube layer number on these properties using molecular dynamics (MD) simulations. The results reveal that the piezoelectric coefficient is positive for BNNTs with odd numbers of layers but negative for those with even numbers of layers. For both, odd and even cases, the magnitude of the piezoelectric coefficient is found to decrease with increasing layer number of BNNTs. A simple continuum mechanics model is developed and reveals that the observed layer number-dependent piezoelectric coefficient of the multi-walled BNNTs mainly originates from their unique inversely stacked structure. In addition, integrating the continuum mechanics model with the MD data leads to an explicit expression for the piezoelectric coefficient of multi-walled BNNTs, which can be easily used to predict the piezoelectric coefficient of BNNTs with various layer numbers.