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 7 nm 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.
