The geometries, formation energies, electronic properties, and reactivities of Stone−Wales (SW) defects in single-walled (8,0) boron nitride nanotubes (BNNTs) were investigated by means of gradient-corrected density functional theory (DFT) computations. SW defects deform BNNTs severely and result in local curvature changes at defect sites. The energies of defect formation increase with increasing tube diameters and are orientation dependent. Depending on the SW defect orientations, additions to central 7-7 ring fusions can be either more or less favorable than to defect-free sites. The reaction energies of model H2 addition are mostly endothermic for defective as well as pristine BNNTs, but reactions at the most favorable sites near SW defect (homoelement N−N bonds followed by the B−B bond sites) are exothermic. This and the fact that the band structures of BNNTs are only slightly changed by SW and vacancy defects as well as by chemical additions at low modification ratios endow BNNTs with great applicati...

Stone−Wales Defects in Single-Walled Boron Nitride Nanotubes: Formation Energies, Electronic Structures, and Reactivity

A Stone–Wales (SW) defect is the simplest topological defect in graphene-like materials and can be potentially employed to design electronic devices . In this paper, we have systematically investigated the formation, structural, and electronic properties of the neutral and charged SW defects in hexagonal boron nitride (BN) using first-principles calculations. The transition states and energy barrier for the formation of SW defects demonstrate that the defected BN is stable. Our calculations show that there are two in-gap defect levels, which originate from the asymmetrical pentagon–heptagon pairs. The local defect configurations and electronic properties are sensitive to their charge states induced by the defect levels. The electronic band structures show that the negative and positive charged defects are mainly determined by shifting the conduction band minimum (CBM) and valence band maximum (VBM) respectively, and the SW-defected BN can realize −1 and +1 spin-polarized charge states. The effects of carbon (C) substitution on neutral and charged SW-defected BN have also been studied. Our results indicate that the C substitution of B in BN is in favour of the formation of SW defects. Structural and electronic calculations show rich charge-dependent properties of C substitutions in SW-defected BN, thus our theoretical study is important for various applications in the design of BN nanostructure-based devices.

Local charge states in hexagonal boron nitride with Stone-Wales defects.

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

Enhancing the piezoelectric properties of boron nitride nanotubes through defect engineering

By using first principles density functional theory simulations, we report detailed geometries, electronic structures and hydrogen (H2) storage properties of boron nitride nanotubes (BNNTs) doped with selective polylithiated molecules (CLi2) We find that unsaturated bonding of Li-1s states with BNNT significantly enhances the system stability and hinders the Li-Li clustering effect, which can be detrimental for reversible H2 storage The H2 adsorption mechanism is explained on the basis of polarization caused by the cationic Li+ of CLi2 molecules bonded with BNNT The incident H2 molecules are adsorbed with BNNT-nCLi2 through electrostatic and van der Waals interactions We find that with a maximum of 50% of CLi2 coverage on BNNT, an H2 gravimetric density of up to 441 wt% can be achieved with adsorption energies in the range of -033 eV per H2, which is suitable for ambient condition H2 storage applications

Capacity enhancement of polylithiated functionalized boron nitride nanotubes: an efficient hydrogen storage medium.

Mechanical and thermal properties of carbon nanotubes and boron nitride nanotubes for fuel cells and hydrogen storage applications: A comparative review of molecular dynamics studies

Using density functional theory, effect of the Stone–Wales (SW) defect on the structural and electronic properties of (6,0) zigzag single-walled boron nitride nanotube (BNNT) under axial tension and compression was investigated at B3LYP/6-31+G(d) level of theory The calculated binding energy for SW defective BNNT is estimated to be smaller than pristine BNNT In Stone–Wales defected BNNT (SW–BNNT), the defect region serves as a nucleation site for fraction It is predicted that the fracture is started from the N–N bond connecting the pentagon and heptagon rings, which is different from fracture mechanism proposed for carbon nanotubes (CNT) with similar location of SW defects Increase in the energy difference between defective and perfect BNNT, ∆E = E
 SW − E
 perfect, was predicted upon axial tension According to our calculation, band gap energy of the SW–BNNT decreases under axial tension and increases under axial compression It is predicted that the SW–BNNT and in turn its tensile form are more suitable than perfect one for photoconductivity applications

Effect of the Stone–Wales (SW) defect on the response of BNNT to axial tension and compression: a quantum chemical study

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Effect of the Stone–Wales (SW) defect on the response of BNNT to axial tension and compression: a quantum chemical study