Enhancing the piezoelectric properties of boron nitride nanotubes through defect engineering

Abstract

In this work, the piezoelectric coefficients of boron nitride nanotubes (BNNTs) containing vacancies were predicted using molecular dynamics simulations (MDS) with a Tersoff potential force field. The piezoelectric coefficients were determined by applying the electric field in the axial direction of BNNTs. The effect of diameter as well as different types of atom vacancies and their positions were taken into consideration. The smaller diameter BNNTs showed higher electromechanical response than larger diameter tubes. Our results reveal that the vacancy defects significantly influence the piezoelectric coefficients of BNNTs, and in some cases, in fact increase the electromechanical response of defective tubes over that of pristine ones. For instance, the piezoelectric coefficient of (8, 0) BNNT with boron (B) mono-vacancy enhances by 17% compared to pristine tube. The converse is true in case of nitrogen (N) mono-vacancies. The removal of B–N bond I, aligned along the tube axis, results in the reduction of piezoelectric coefficient of (8, 0) BNNT by 41%. The removal of bond II, inclined to the tube axis, increases the piezoelectric coefficient of (8, 0) BNNT by 13%. The same phenomenon was observed for other zigzag BNNTs containing mono-vacancies and di-vacancies (absence of B–N bonds). The results showed that the piezoelectric coefficients of BNNTs strongly depend on the position of vacancies and the maximum enhancement was observed as 17% and 13% for B mono-vacancy and di-vacancy of B–N bond II, respectively, over that of pristine (8, 0) BNNT. Apart from mono- and di-vacancies, we also considered multi-vacancies in BNNTs and observed maximum enhancement by as much as 36% in the piezoelectric coefficient of defective (8, 0) BNNT containing 2B and 2 N vacancies at particular locations. Moreover, the concerned results reveal that the enhancement of electromechanical response largely depends on the symmetry of vacancy defect pore and not the vacancy concentration. The present work shows that we can enhance/alter the piezoelectric properties of BNNTs via a novel pathways of defect engineering by introducing different types of vacancies and changing their positions to suit a particular NEMS applications.