Zigzag Boron Nitride Nanotubes Research Articles

A comparative simulation study of piezoelectric properties in zigzag and armchair boron nitride nanotubes: by discovering a pioneering protocol

A comparative simulation study of piezoelectric properties in zigzag and armchair boron nitride nanotubes: by discovering a pioneering protocol

Analyze the temperature-dependent elastic properties of single-walled boron nitride nanotubes by a modified energy method

The elastic properties of boron nitride nanotubes (BNNTs) were investigated utilizing an enhanced energy method. By considering small deformations and applying the principle of minimum potential energy, the variations in atomic bonds and bond angles within the nanotube structure were determined. The modified model incorporated the contribution of inversion energy to the overall potential energy of the system, leading to the derivation of analytical expressions for the Young's modulus, shear modulus, and strain energy of both armchair and zigzag BNNTs under varying temperatures. The results indicate that compared to zigzag BNNTs, the impact of inversion energy on the elastic constants of armchair BNNTs is more significant, especially at small diameters (<1 nm). In thermal environment, this study demonstrates that the change in Young's modulus of BNNTs is lower than that of carbon nanotubes (CNTs), confirming the superior thermal stability of BNNTs over CNTs. Furthermore, molecular structure mechanics (MSM) and continuum mechanics models were employed to analyze the strain energy of BNNTs. The effects of different bonds, bond angles, and inversion angles on strain energy were analyzed in a thermal environment, revealing distinct differences between the two types of BNNTs. These findings provide more accurate theoretical guidance for thermal applications based on the stretching of BNNTs.

Zigzag boron nitride nanotube functionalization as a sensor for the recognition of group IIA (Mg2+, Ca2+) metal ions, quasi-metal (Si2+, Ge2+) ions, and transition metal (Cu2+, Zn2+) ions: a computational study.

Boron nitride nanotubes (BNNTs) provide an exceptional and sophisticated platform for detecting metal ions with high surface area and remarkable chemical stability. Metal cations tend to bind to the surface of BNNTs, which leads to significant changes in the electrical properties of nanotubes. BNNT-based metal ion sensors have shown promising results in various applications, including water quality monitoring, biomedical research, industrial quality control, and environmental monitoring. In the present study, we have explored the electronic sensitivity of the BNNT to metal ions (Si2+, Ge2+, Cu2+, Zn2+, Mg2+, and Ca2+). The interaction between the ions with the pristine BNNT is performed in the solution phase. The results show that ion adsorption on the nanotube surface is exothermic and favorable. The density of states calculation is presented to investigate the electronic properties of the nanotube during the adsorption process. The results display that an increase in the electrical conductivity of the complexes accompanies the reduction in the energy gap. Based on the obtained data, the Si2+ and Ge2+ cations adsorbed on the BNNT with satisfactory Eg changes (%ΔE) can be promising candidates for better sensing ability. All calculations are conducted within the density functional theory (DFT) using the ωB97XD functional and 6-31G(d,p) basis set. The present approach incorporates the utilization of empirical atom-atom dispersion in conjunction with long-range correction. The calculations are performed using the quantum chemistry package GAMESS, and the obtained results are visualized by employing the GaussView 6.0.16 program.

Predicting Quantum-Mechanical Partial Charges in Arbitrarily Long Boron Nitride Nanotubes to Accurately Simulate Nanoscale Water Transport.

Single-walled boron nitride nanotubes (BNNTs) have been explored for various applications, ranging from water desalination to osmotic power harvesting. However, no simulation work so far has modeled the changes in the partial charge distribution when a flat sheet is rolled into a tube, hindering the ability to perform accurate molecular dynamics (MD) simulations of water flow through BNNTs. To address this knowledge gap, we employ electronic density functional theory (DFT) calculations to precisely estimate quantum-mechanically derived partial charges on boron (B) and nitrogen (N) atoms in BNNTs of varying lengths and diameters. We observe a spatially varying charge distribution inside both armchair and zigzag nanotubes of finite lengths. Performing DFT calculations for longer BNNTs is computationally intractable, even with state-of-the-art computing resources. To solve this issue, we devise a charge assignment scheme to predict partial charges for longer BNNTs using DFT data for shorter nanotubes, thus overcoming the need to perform more expensive DFT calculations. We show that these charges reproduce the electrostatic potential predicted from first-principles simulations. Subsequently, we carried out MD simulations to predict the effect of the charge distribution inside BNNTs on water flow enhancement via them. We find that using uniform charges leads to an underprediction in flow enhancement, as compared to using quantum-mechanical charges for both armchair and zigzag BNNTs. We also incorporate atomic vibrations into our simulations and show that these vibrations lead to a reduction in the water flow through aperiodic BNNTs. Our work demonstrates the requirement of a quantum-mechanical charge assignment scheme for BNNTs and evolves a framework to assign charges to nanotubes of arbitrary length, thus allowing realistic MD simulations of long BNNTs using accurate partial charges.

Building Molecular Nanomagnets by Encapsulating Lanthanide Ions in Boron Nitride Nanotubes: Ab Initio Investigation.

Lanthanide-based single-ion magnets have attracted much interest due to their great potential for information storage at the level of one molecule. Among various strategies to enhance magnetization blocking in such complexes, the synthesis of axially symmetric compounds is regarded as the most promising. Here, we investigate theoretically the magnetization blocking of several lanthanide ions (Tb3+, Dy3+, Ho3+, Er3+, and Tm3+) encapsulated in highly symmetric zigzag boron nitride nanotubes (BNNTs) of different diameters with ab initio methodology. We found that Tb3+@(7,0)BNNT, Dy3+@(7,0)BNNT, and Tm3+@(5,0)BNNT are suitable SIM candidates, while the other investigated complexes from this series show no signs of magnetization blocking owing to a hard competition between contributions to the crystal field of the lanthanide ion from neighboring and more distant atoms of the nanotube.

Engineering and controlling the electronic properties of zigzag and armchair boron nitride nanotubes with various concentrations of oxygen impurities

This research underscored the comprehension of the electronic properties of the various diameters for zigzag and armchair single-wall boron nitride (ZSWBNNTs and ASWBNNTs) under various concentrations of oxygen impurities. The electronic properties of these tubes are investigated by using the first density functional theory (DFT), which implemented in the QUANTUM ESPRESSO package. Results show that the electronic properties of all these tubes can be controlled by using different concentrations of oxygen impurities. In the pristine case, the electronic band gap of these tubes is deepened on the diameter. So, the electronic band gap is increased by increasing the diameter of the tube. Nevertheless, these properties are changed and affected by various concentrations of oxygen impurities. The electronic band gap of ZSWBNNTs reduced by using one and two -hexagonal of oxygen impurities, and the behavior of ASWBNNTs changed from insulator to semiconductor properties by using a 2-hexagonal of oxygen impurities. Our investigation revealed for the first time that the behaviors of ZSWBNNTs and ASWBNNTs are changed from semiconductor and insulator to metallic with seven oxygen impurities. Then, there are very fascinating results. Also, the electronic band gap doesn't only depend on the impurity concentration, but also depends on the geometrical pattern of oxygen impurities in the ASWBNNTs.

Quantum Chemical Approaches to the Encapsulation of Parathion, Chlorpyrifos and Coumaphos by Armchair and Zigzag Boron Nitride Nanotubes Doped with Aluminum

Boron nitride nanotubes have been widely used as drug delivery vehicles and for the controlled release of targeted therapeutic drugs. In this study, we calculated the encapsulation efficiencies of three organophosphorus pesticides, parathion, chlorpyrifos, and coumaphous, using quantum chemical methods. The results show that the encapsulation energy of zigzag BNNT(20,0) is lower than that of armchair BNNT(12,12) to encapsulate parathion. Al doping helps to decrease the encapsulation energy and Al-doped zigzag BNNT(20,0) + parathion has the greatest binding affinity. In addition, the energy gap of armchair BNNT(12,12) encapsulating organophosphorus pesticides changed significantly. Al doping reduces the band gap of boron nitride nanotubes. Al-doped armchair BNNT(12,12) has the strongest electron-accepting ability and is a promising sensor material.

Density Functional Theory Investigation on the Structural and Electronic Properties of Pristine, Vacancy, and Group IV Doped Zigzag Boron Nitride Nanotubes

In this work, density functional theory (DFT) calculations were conducted to study the structural and electronic properties of pure, vacancy, and group IV [i.e. carbon (C), silicon (Si), and germanium (Ge) atoms] doped boron nitride nanotubes (BNNTs). The DFT computational results obtained agree well with the literature results. The calculated B−N bond distances obtained in this study are about 1.44 Å – 1.47 Å. Among seven BNNTs, the optimized B35GeN36H12 holds the lowest local energy minimum value in this study Moreover, the structure of B35CN36H12 possesses the smallest HOMO−LUMO energy (2.17 eV) among nine BNNT models considered. The boron (B) atoms hold the positive charges, and the negative charges fall on the nitrogen (N) atoms in this work. Similar results are reported to the molecular electrostatic potentials (MEPs) of studied BNNTs. The distributions of positive and negative electrostatic potentials fall on the regions of N− and B−tips of BNNT frameworks, respectively in this report. The DFT calculations reported that the spin densities were mainly concentrated in the regions around group IV elements, such as C, Si, and Ge atoms. Therefore, we believe that these computed results will provide useful information on the adsorption of hydrogen molecules on the BNNT frameworks in the future.

Ni-doped boron nitride nanotubes as promising gas sensing material for dissolved gases in transformer oil

This paper reports that the transition metals (TM), including Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, are substituted in a perfect zigzag (8, 0) boron nitride nanotubes (BNNTs) at B-site and N-site to improve the adsorption performance of intrinsic BNNTs towards oil-dissolved gases (H 2 , CH 4 , and C 2 H 2 ), particularly C 2 H 2 . In this regard, the quantum chemical calculations are performed based on the density functional theory (DFT). The results show that the C 2 H 2 gas adsorption characteristic of BNNTs is selectively enhanced due to the intervention of the TM atom. The Co B , Ni B, Cu B, Zn B, and Zn N are preliminarily selected as potential gas sensors for C 2 H 2 gas based on their suitable range of adsorption energy. The sensitivity, selectivity, and recovery time of the above five structures are compared. It is found that Ni B is a superior sensing material with exceptionally high sensitivity and selectivity. Moreover, the Ni B presented preferable desorption properties for C 2 H 2 gas at room temperature, making it promising for a chemical resistance-type gas sensing device. The analysis of charge transfer and density of states illustrates that the Ni B donates electrons to C 2 H 2 , proving its superiority over the adsorption properties for C 2 H 2 gas over H 2 and CH 4 . The suitable recovery time (2.3 s), extremely high gas response value (494383%), and stable chemisorption demonstrate that the Ni-doped BNNTs at B-site can be a superior chemical gas sensor for C 2 H 2 gas at room temperature.

First-principles calculations of nickel, cadmium, and lead nanoclusters adsorption on single-wall (10,0) boron-nitride nanotube

The aim of this work is to elucidate and characterize the interaction of heavy metals like nickel (Ni), cadmium (Cd) and lead (Pb) with (10,0) zigzag boron nitride nanotubes (BNNT). All the calculations were done using first principle method within the density functional theory. The binding energies’ results indicate that the adsorptions of Ni and Cd are favorable (negative value) and the adsorption of Pb is non favorable (positive value). Between the three metals, Ni has the lower binding energy (strongest interaction) and induced the major modifications on the electronic structure. Furthermore, they are quite different values indicate great adsorption selectivity. Both Ni and Pb trigger a change in the magnetism of the nanotube through the induction of spin polarization. All three metals produced a band-gap reduction and maintain the semiconductor behavior of the BNNT. The binding energies and the BNNT electronic properties’ changes after the interaction of metals with nanotube suggest that BNNT can be used as filters and sensors of such metals.

A two-section beam element to model the B-N covalent bonds in boron nitride nanotubes

The ability of molecular mechanics to model the covalent bonds with equivalent elements is limited to the bonds connected with similar atom pairs. When dissimilar atoms are connected by covalent bonds, single-sectioned beam or spring elements could not capture the physical properties of the bond. In this respect, a molecular mechanics based two-sectioned beam element was formulated based on strain energy minimization and was used to model the elastic and vibrational characteristics of the boron nitride nanotubes (BNNT). Inconsistent conclusions given by the conventional molecular mechanics models were all rectified by the present formulation. It was shown that the armchair BNNTs has higher Young's modulus than that of zigzag counterparts. This was captured by the model with two-section beam elements, while single-section beam and equivalent spring elements are unable to predict this conclusion. The shear modulus of the zigzag BNNTs were 10 to 17 percent higher than the armchair counterparts.

Structural, magnetic, and electronic properties and stability of 3d-TM substituted single-walled zigzag BNNTs: A density functional theory study

We investigate the effects of the substitution of all the first series transition-metal (TM) atoms on the physical properties of (10,0) boron nitride nanotube (BNNT) using the DFT calculation. Three interesting results are as follows: First, the formation energies show a more stable system for the born (B) site substitution than nitrogen (N) site substitution. Second, reducing the bandgap of the TM-substituted BNNT with respect to the pristine BNNT can be mainly related to the presence of the new impurity states induced near the Fermi level by the d electrons of the TM atom, and a half-metal behavior has been obtained for Ti-, V-, Ni-, Co-, Cu-substitution at B-site and Fe-, V-, Ni-substitution at N-site. Third, besides the appearance of two up-and-down-spin channels, a new spin-crossover has been observed for Fe-, Ni-, Co-, Cu-substitution at B-site and Ti-, V-substitution at N-site which make them suitable to use in spintronic applications.

Axial deformation effects on hydrogen storage of Ni decorated (8,0) zigzag single-walled boron nitride nanotubes: a DFT study

The effect of axial deformation on tuning the hydrogen storage of nickel functionalised (8,0) zigzag boron nitride nanotube is investigated by using density functional theory calculations. The assessment has been carried out based on the adsorption of molecular hydrogen with the binding energy lying in the desirable energy window, charge transfer, the density of states, pairwise and nonpairwise additivty, frontier orbital band gaps, isosurface plots, polarizabilities and hyperpolarizabilities, simulated Infrared (IR) and Raman (R). The numerous changes in adsorption energy of H2 upon relaxation or compression of only (1%) strain points to the sensitivity of H2 binding to axial deformation effects. The calculated pairwise and non-pairwise additive components show that the role of the BNNT is not restricted to support the metal. Spectral analysis additionally as polarizability and hyperpolarizability calculations characterise the relaxed structure (Z = 1.01), that H2 adsorption energy (−0.552 eV) is within the suggested energy vary for hydrogen storage, to be energetically additional desirable than the compressed structure (Z = 0.99). The results provide some way to manage and characterise the hydrogenation process of metal functionalised BNNTs by strain loading.

Collective plasmonic oscillations of zigzag boron-nitride nanotubes in the presence of Holstein phonons

In this paper, we study theoretically both dynamical and static charge susceptibilities of zigzag boron-nitride nanotube due to the effects of electron-phonon interaction. One can find the plasmonic oscillation modes of the system using the imaginary part of the dynamical charge susceptibility function. For this purpose, we implement Green's function approach in the context of the Holstein model Hamiltonian. According to the linear response theory, the charge response function will be obtained by calculating the correlation function of charge density-density operators. We also exploit the random phase approximation in order to correct the charge susceptibility due to the electron-phonon interaction. In addition, we present the static charge structure factor which can be a criterion for charge ordering of the system. Especially the effect of electron-phonon coupling, gap parameter, chemical potential, next-to-nearest-neighbor hopping amplitude, and tube diameter on the plasmonic modes of the system. The results indicate a change in the intensity, frequency position of sharp peaks, and the number of those in the imaginary part of the dynamical charge susceptibility function of zigzag boron-nitride nanotube system. Finally, the temperature behavior of the static charge structure factor of zigzag boron-nitride nanotube is studied and the effect of the mentioned parameters on this function has been investigated.

Potential applications of armchair, zigzag, and chiral boron nitride nanotubes as a drug delivery system: Letrozole anticancer drug encapsulation

A density functional theory calculation has been applied to be investigated the ability of (12,12) armchair, (21,0) zigzag, and (18,5) chiral boron nitride nanotubes (BNNT) as the drug nanocarrier in Letrozole delivery. For this purpose, the behavior of drug Letrozole when encapsulated into different chirality of BNNTs with the same diameter was studied. Moreover, the reduced side effects and increasing solubility of Letrozole can be achieved by encapsulation in boron nitride nanotubes. A complete understanding of the encapsulation process of drug molecules into BNNTs is necessary for the development of drug delivery systems. Geometry optimizations of the three types of BNNTs and drug Letrozole have been performed by means of density functional theory calculation, using the functional wb97xd with 6-31G basis set. The results indicate that Letrozole is encapsulated in cavity of the nanotubes. The structural and the electronic properties of encapsulated Letrozole in the studied systems have been also predicted by quantum mechanical descriptors such as equilibrium distances, highest occupied molecular orbital (HOMO)—lowest unoccupied molecular orbital (LUMO) energy gap. The quantum mechanical calculations verify that the armchair and the chiral single-walled boron nitride nanotubes could spontaneously adsorb Letrozole in a chemisorption process while the physisorption process plays a large role in adsorption within the zigzag single-walled boron nitride nanotube.

Defect-Mediated Piezoelectricity in Boron Nitride Nanotube

Introduction A zigzag boron nitride nanotube (ZBNNT) has a large intrinsic polarized dipole and a piezoelectric tunability with crystal chirality, nanotube diameter, and point defect. The piezoelectric coefficients (e33) of 8-ZBNNT with the VIA-group defects of SN and SeN are estimated to be 18.7×10-2 C/m2 and 14.9×10-2 C/m2, respectively. The coefficients of defect-mediated 8-ZBNNT are 97% and 57% bigger than that of pristine 8-ZBNNT. The elastic modulus of 8-ZBNNT is decreased due to the VIA-group defects, but is increased for the larger number of unit cells along zigzag rolling direction. The electronic band gap of 8-ZBNNT is reduced due to the VIA-group defects. The large piezoelectricity enhancement of 8-ZBNNT with VIA-group defect is attributable to the enhanced piezoelectricity from ionic contribution. Therefore, the unprecedented defect-mediated 8-ZBNNT provides a new material platform of mechanoelectronic devices for nanoscale sensors and energy conversions. Modeling and methodology Figure 1 shows the schematic of a single wall 8-ZBNNT with an atomic defect. The supercell is in a simple orthorhombic box with periodic boundary condition in 30 Å × 30 Å × Lc where Lc is the lattice parameter along the transport direction. The green atom “A” indicates the defect of a single substitution atom per a supercell. The average bond length is defined as the average length of atomic bond between the defect doping atom and the neighboring boron atoms. The first principle calculations were carried out by using the Virtual Nanolab Atomistix ToolKit (ATK) package with the density functional theory (DFT). The localized density approximation (LDA) exchange correlation with a double zeta polarized (DZP) basis was used with a mesh cut-off energy of 150 Ry. All atomic positions and lattice parameters were optimized by using the generalized gradient approximations (GGA) with the maximum Hellmann Feynman forces of 0.05 eV/Å, which was sufficient to obtain relaxed structures. The maximum number of fully self-consistent field (SCF) iteration steps was set to 100. Defect-mediated piezoelectricity The table I includes the piezoelectric coefficient (e33) and average bond length (a0) of 10- and 8-ZBNNT with different kinds of defects including SW deformation, IVA-group, and VIA-group defects within one supercell. Among the defects in ZBNNT, a single nitrogen vacancy or SW defect diminishes the piezoelectric coefficient (e33) of 10- and 8-ZBNNT. However, the atomic defects of IVA- and VIA-group elements in a nitrogen site enhance the piezoelectric coefficient. The piezoelectric coefficient of VIA-group defect is higher than that of IVA-group defect. The piezoelectric coefficient e33 of chalcogen defect SN and SeN in 8-ZBNNT is enhanced 97% and 57% from 9.49×10-2 C/m2 to 18.7×10-2 C/m2 and 14.9×10-2 C/m2, respectively, compared to that of pristine 8-ZBNNT. The table I includes the elastic modulus of pristine10-ZBNNT and 8-ZBNNT and the ZBNNT with defects. The elastic modulus of 10- and 8-ZBNNT with defects is smaller than that of pristine 10- and 8-ZBNNT. The elastic modulus of SW defects in ZBNNT is increased compared to that of pristine 10- and 8-ZBNNT. The structure with smaller elastic modulus has the larger strain response to the constant external stress. Therefore, the ZBNNT with IVA- and VIA-group atomic defects has an efficient response to the external stress for piezoelectric applications. 8-ZBNNT of SN and SeN with the smaller elastic modulus have the larger e33 compared to the structure with ON. Defect-mediated electronic band structure Figure 2 shows the electronic band structure of 8-ZBNNT with (a) pristine structure and (b) defects of ON, SN and SeN. The group VIA-group defects in 8-ZBNNT are n-type doping because the Fermi level is located in the conduction band while the VIA-group defects in 8-ZBNNT are p-type doping. The bandgap in 8-ZBNNT is also reduced from 3.37 eV to 3.16 eV, 3.12 eV and 3.20 eV for the VIA-group defect of ON, SN and SeN, respectively. However, the band gaps of 8-ZBNNT with the IVA-group defects of CN, SiN and GeN is slightly widened to 3.38 eV, 3.49 eV and 3.50 eV compared to the band gap 3.37 eV of pristine 8-ZBNNT, respectively. Conclusions The piezoelectricity of ZBNNT is significantly enhanced by atomic defects. The piezoelectric coefficients (e33) 8-ZBNNT with SN and SeN defects are increased up to 97% and 57%, respectively. The electronic band gap of 8-ZBNNT with defects is reduced. The large piezoelectricity enhancement of 8-ZBNNT with VIA-group defect is attributable to the enhanced piezoelectricity from ionic contribution. Therefore, the unprecedented defect-mediated 8-ZBNNT provides a new material platform of mechanoelectronic devices for nanoscale sensors and energy conversions. Acknowledges This work is supported by ARO W911NF-15-1-0535, NSF HRD-1137747, and NASA NNX15AQ03A. Figure 1

Electric Field Effects on Buckling Analysis of Boron–Nitride Nanotubes Using Surface Elasticity Theory

In this paper, the axial buckling of boron nitride nanotubes (BNNTs) is investigated by considering the effects of surface and electric field. To achieve this purpose, the surface elasticity theory is exploited and the results are compared with the molecular dynamic simulation in order to validate the accuracy of the applied theory. In the molecular dynamics simulation, the potential between boron and nitride atoms is considered as Tersoff type. The Timoshenko beam theory is adopted to model BNNT. Moreover, two types of zigzag and armchair BNNTs are considered. In this study, the effects of surface, electric field, length, and thickness of BNNT on the critical buckling load are investigated. According to the results, the critical load of zigzag BNNT depends on the electric field. However, the electric field would not affect the critical load of the armchair BNNT. It should be noted that the surface residual tension and surface Lamé’s constants of BNNT have considerable impact on the critical load of BNNT. For lower values of electric field and smaller dimensions of BNNT, the critical load would be more dependent on the surface effect regarding the results. Furthermore, as an efficient non-classical continuum mechanic approach, the surface elasticity theory can fill the potential gap between the classical continuum mechanic and molecular dynamics simulation.

Electromechanical buckling analysis of boron nitride nanotube using molecular dynamic simulation

In this paper, the effect of electric field on axial buckling of boron nitride nanotubes is investigated. For this purpose, molecular dynamics simulation and continuum mechanics are used for the first time simultaneously. In molecular dynamics simulation, the potential between boron nitride atoms is considered as Tersoff and Timoshenko beam theory is used in continuum mechanics. In this paper, buckling of zigzag and armchair boron nitride nanotubes are investigated. Here, the effects of the electric field and the length of the boron nitride nanotube on the critical load are investigated and it is shown that the effect of the electric field is different with respect to the arrangement of atoms in the boron nitride nanotubes. In fact, the electric field creates axial and torsional loads on the zigzag and armchair nanotube, respectively. Axial buckling of the zigzag nanotube is dependent on the electric field, whereas in the armchair nanotubes, the electric field changes have no effect on the axial buckling. To better understand the impact of the electric field on axial buckling, these results are compared with the continuum mechanics.

Effect of Stone–Wales defects on the mechanical behavior of boron nitride nanotubes

The transversely isotropic response of pristine as well as defective boron nitride nanotubes (BNNTs) containing Stone–Wales (SW) defects was comprehensively studied via molecular dynamic simulations with a three-body Tersoff force field. The elastic properties and the failure behavior of BNNTs were studied under the transversely isotropic loading conditions, namely uniaxial tension, twisting moment, in-plane shear and in-plane biaxial tension. The effect of chirality, diameter and SW defect density was taken into consideration. The failure mechanism of BNNTs under each loading condition was explained in detail. Our study reveals that the elastic moduli of zigzag BNNTs are higher than for armchair tubes and decrease as the diameter of the tube increases. The effect of SW defects is found to be higher on the elastic properties of smaller diameter BNNTs than for larger diameter tubes, regardless of chirality. The higher defect density reduces the axial Young’s modulus, shear, plane strain bulk and in-plane shear moduli by 11%, 18%, 9% and 7%, respectively. The SW defects affect the (1) longitudinal shear moduli of BNNTs more profoundly irrespective of chirality and (2) the mechanical behavior of zigzag BNNTs stronger compared to armchair ones. It is also found that the mechanical properties of BNNTs are functions of chirality and diameter, especially for small diameter tubes.

Enhancing the piezoelectric properties of boron nitride nanotubes through defect engineering

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.