Piezoelectric and elastic properties of multiwall boron-nitride nanotubes and their fibers: A molecular dynamics study

Abstract

Piezoelectric and elastic properties of multiwall boron-nitride nanotubes are studied using a classical molecular dynamics model with an incorporated strain-dependent dipole potential energy term. The results are applied to predict the piezoelectric and elastic properties of a boron-nitride nanotubes fiber with experimentally obtained diameter and wall number distribution of the nanotubes synthesized by high-temperature pressure methods. Nanotubes of (m, 0)-type (zig-zag nanotubes) of up to 10 wall layers and up to 7nm in diameter are simulated in tension along the tube axis. While the tensile stiffness of all of the simulated nanotubes increases linearly with their radius and the number of wall layers, a substantial difference in the piezoelectric response is found between nanotubes of even and odd number of wall layers due to the particular stacking sequence of the boron-nitride layers. The piezoelectric polarization per unit length of odd-layer boron-nitride nanotubes increases linearly with the tube radius, but decreases with the number of layers. By contrast, the piezoelectric polarization of even-layer nanotubes is independent of the radius, but increases linearly with the number of layers. Analytical expressions for the multiwall boron-nitride nanotubes stiffness and piezoelectric coefficients are provided for use in continuum mechanics finite-element models.