Boron Nitride Polymorphs Research Articles

Exploration of novel boron nitride polymorphs: High-throughput screening combined with multi-task orbital crystal graph convolutional neural network (MT-OCGCN)

In response to the limitations of traditional material property prediction methods, we have developed a Multi-task Orbital Crystal Graph Convolutional Neural Network (MT-OCGCN). This innovative model allows for sharing parameters and computational resources, significantly improving prediction efficiency and accuracy. Experimental comparisons show that the model can achieve multi-task prediction with high accuracy for both strong and weak correlation properties, this offers an efficient approach for computational materials screening and design. Combined with high-throughput screening has resulted in the discovery of 13 new boron nitride polymorphs in the P21/c phase, among which 7 are characterized as wide direct band gap semiconductors. Furthermore, we have comprehensively analyzed the mechanical, thermal, and electronic properties of these new boron nitride polymorphs. It can be asserted that MT-OCGCN has the capability to precisely forecast the physical properties of novel structures that are absent from current databases.

Study of the novel boron nitride polymorphs: First- principles calculations and machine learning

This study explores two new boron nitride polymorphs, namely C2221 BN and I-4 BN, characterized by sp2 hybridization. The investigation is conducted through first-principles calculations, including assessments of their structural properties, stability, elastic properties, anisotropy, and electronic properties. The newly discovered boron nitride polymorphs exhibit mechanical stability, dynamic stability, and thermodynamic stability, as ascertained by analyzing their elastic constants, phonon spectra, and associated enthalpies. The B/G values for both C2221 BN and I-4 BN far exceed the threshold of 1.75, thus confirming that they are ductile materials. The BN polymorphs investigated in this work exhibit different degrees of anisotropy in Young's modulus, shear modulus, and Poisson's ratio. Meanwhile, two different datasets were trained using four machine learning algorithms, and the random forest model with the m2ax dataset showed a high fitting degree, small error, and good stability. Then, the machine learning model, which has undergone training, is used to predict the elastic modulus of boron nitride polymorphs. Upon comparing the computed GGA values with the experimental values of c-BN, it is evident that the random forest model outperforms in accurately predicting the elastic modulus of boron nitride polymorphs.

A First-Principle Study of Two-Dimensional Boron Nitride Polymorph with Tunable Magnetism

Using the first-principles calculation, two doping two-dimensional (2D) BN (boron nitride) polymorphs are constructed in this work. The two doping 2D BN polymorphs B5N6Al and B5N6C sheets are thermally stable under 500 K. All the B6N6, B5N6Al, and B5N6C sheets are semiconductor materials with indirect band gaps on the basis of a hybrid functional. The anisotropic calculation results indicate that Young’s modulus (E) and Poisson’s ratio (v) of the B6N6, B5N6Al, and B5N6C sheets are anisotropic in the xy plane. In addition, the magnetic properties of the B6N6, B5N6Al, and B5N6C sheets have also been investigated. According to the calculation of the magnetic properties, B6N6 sheet does not exhibit magnetism, while it shows weak magnetism after doping carbon atom to the BN sheet. This paper explores the influence mechanism of doping different atoms on the basic physical properties of two-dimensional BN sheets. It not only constructs a relationship between structure and performance but also provides theoretical support for the performance regulation of BN materials.

Wetting and Brazing of Superhard Materials Based on Dense Boron Nitride Polymorphs with Braze Alloy Melts

Wetting and Brazing of Superhard Materials Based on Dense Boron Nitride Polymorphs with Braze Alloy Melts

On functional boron nitride: Electronic structures and thermal properties

• Summary of boron nitride polymorphs and structural stabilities. • Electronic and thermal transport in boron nitride, from bulk to lower dimensions. • Summary of state-of-the-art study on atomic-layer-deposition growth of boron nitride. • Current application of boron nitride and future perspectives. The past two decades have witnessed extensive explorations of boron nitride (BN) largely due to its unique optoelectronic properties, mechanical robustness, high thermal conductivity, thermal and chemical stability. Crystal growth and functional engineering of BN thin film structures as well as their integrations with two-dimensional materials for advanced applications have been attracting increasing interest in recent years. Here, we have reviewed the basic structural, electronic, and thermal transport properties of BN, especially hexagonal BN both in bulk and reduced dimensionalities. This is followed by a thorough account of progress in atomic layer deposition (ALD) of BN, which has the advantages of being able to grow on 3D surface and control the film thickness in atomic level. Future perspectives are provided through discussing the potential applications of BN along with the material synthesis.

Two new BN polymorphs with wide-bandgap

Two boron nitride polymorphs, denoted as P-62m BN and I-43d BN, are investigated in this work: P-62m BN with sp2 + sp3 hybridizations, and I-43d BN with sp3 hybridization. P-62m BN and I-43d BN are mechanically, thermally, and dynamically stable. As predicted by the electronic band structure, both P-62m BN and I-43d BN are wide band gap semiconductor materials, and P-62m BN is an ultrawide band gap semiconductor material because the band gap of P-62m BN exceeds that of Ga2O3 and diamond. Meanwhile the band gap of I-43d BN is larger than that of ZnO, GaN and SiC. Both the B/G ratios of P-62m BN and I-43d BN are smaller than 1.75, which confirms that they are brittle materials. The P-62m BN and I-43d BN show different degrees of elastic anisotropy in Young's modulus in this work. In addition, to better distinguish these BN polymorphs in the future, X-ray diffraction patterns of P-62m BN and I-43d BN are also studied.

Two novel large-cell boron nitride polymorphs

Based on density functional theory, two novel sp2-hybridized cubic boron nitride (cP128 BN and cP144 BN) structures are proposed. Analysis of phonon spectra, elastic constants and molecular dynamics simulation energy changes at 800 K indicates that cP128 BN and cP144 BN have dynamical stability, mechanical stability and thermodynamic stability. The bulk to shear modulus ratios for cP128 BN and cP144 BN are calculated to be 2.28 and 2.26, and the Poisson's ratios are calculated to be 0.31 and 0.31, respectively, indicating that both novel BN polymorphs are ductile. Compared with the anisotropy of cP128 BN, c-BN, P213 BN and Pm-3n BN in the primary plane, cP144 BN has large anisotropy in the primary planes. Moreover, both cP128 BN and cP144 BN are wide band gap semiconductors, in which cP128 BN has a direct band gap with a band gap of 3.297 eV, and cP144 BN can be regarded as an indirect band gap semiconductor with a band gap of 2.824 eV. Through the design and study of these two novel electronic materials, it can be found that they have good prospects for application in the industry for optoelectronic devices, as well as high temperature, high power and other electronic devices.

Diffusion Monte Carlo Study on Relative Stabilities of Boron Nitride Polymorphs

Although Boron nitride (BN) is a well-known compound widely used for engineering and scientific purposes, the phase stability of its polymorphs, one of its most fundamental properties, is still under debate. The ab initio determination of the ground state of the BN polymorphs, such as hexagonal and zinc-blende, is difficult because of the elusive Van der Waals interaction, which plays a decisive role in some of the polymorphs, making quantitative prediction highly challenging. Hence, despite multiple theoretical studies, there has been no consensus on the ground state yet, primarily due to contradicting reports. In this study, we apply a state-of-the-art ab initio framework - fixed-node diffusion Monte Carlo (FNDMC), to four well known BN polymorphs, namely hexagonal, rhombohedral, wurtzite, and zinc-blende BNs. Our FNDMC calculations show that hBN is thermodynamically the most stable among the four polymorphs at 0 K as well as at 300K. This result agrees with the experimental data of Corrigan~{\it et al.} and Fukunaga. The conclusions are consistent with those obtained using other high-level methods, such as coupled cluster. We demonstrate that the FNDMC is a powerful method to address polymorphs that exhibit bonds of various forms. It also provides valuable information, like reliable reference energies, when reliable experimental data are missing or difficult to access. Our findings should promote the application of FNDMC for other van der Waals materials.

Novel Boron Nitride Polymorphs with Graphite-Diamond Hybrid Structure

Both boron nitride (BN) and carbon (C) have sp, sp 2 and sp 3 hybridization modes, thus resulting in a variety of BN and C polymorphs with similar structures, such as hexagonal BN (hBN) and graphite, cubic BN (cBN) and diamond. Here, five types of BN polymorph structures are proposed theoretically, inspired by the graphite-diamond hybrid structures discovered in a recent experiment. These BN polymorphs with graphite-diamond hybrid structures possess excellent mechanical properties with combined high hardness and high ductility, and also exhibit various electronic properties such as semi-conductivity, semi-metallicity, and even one- and two-dimensional conductivity, differing from known insulators hBN and cBN. The simulated diffraction patterns of these BN hybrid structures could account for the unsolved diffraction patterns of intermediate products composed of so-called “compressed hBN” and diamond-like BN, caused by phase transitions in previous experiments. Thus, this work provides a theoretical basis for the presence of these types of hybrid materials during phase transitions between graphite-like and diamond-like BN polymorphs.

All sp2 hybridization BN polymorphs with wide bandgap

Four new boron nitride polymorphs hP24 BN, hP18-I BN, mP36 BN, and hP18-II BN with sp2 hybridization are investigated in this study by first-principles calculations, including the structural properties, stability, elastic properties, anisotropy, and electronic properties. Predicted by the electronic band structure, all the BN polymorphs in hP24, hP18-I, mP36, and hP18-II phase are wide bandgap semiconductor materials with a bandgap of 2.97–4.72 eV. Meanwhile, the bandgap of hP24 BN is larger than that of ZnO, and the bandgaps of hP18-I BN, mP36 BN, and hP18-II BN are larger than those of GaN and SiC. The new boron nitride polymorphs have mechanical stability, dynamic stability, and thermodynamic stability by analyzing the elastic constants, phonon spectra, and related enthalpies. The values of B/G of hP24 BN, hP18-I BN, mP36 BN, and hP18-II BN are all larger than 1.75, which confirms that they are ductile materials. Their densities are around 2.100 g/cm3, which are smaller than that of the c-BN (3.466 g/cm3). BN polymorphs in this study show different degrees of anisotropy in Young's modulus, and hP24 BN has the largest anisotropy in Young's modulus, while mP36 BN displays the smallest Young's modulus anisotropy.

P213 BN: a novel large-cell boron nitride polymorph

A new boron nitride polymorph, P213 BN (space group: P213), is investigated by first-principles calculations, including its structural properties, stability, elastic properties, anisotropy and electronic properties. It is found that the new boron nitride polymorph P213 BN is mechanically, dynamically and thermodynamically stable. The bulk modulus (B), shear modulus (G) and Young’s modulus of P213 BN are 91 GPa, 41 GPa and 107 GPa, respectively, all of which are larger than that of Y carbon and TY carbon. By comparing with c-BN, the Young’s modulus, shear modulus and Poisson’s ratio of P213 BN show tiny anisotropy in the (001), (010), (100) and (111) planes. At the same time, in contrast with most boron nitride polymorphs, P213 BN is a semiconductor material with a smaller band gap of 1.826 eV. The Debye temperature and the anisotropic sound velocities of P213 BN are also investigated in this work.

Determination of the optical bandgap of the Bernal and rhombohedral boron nitride polymorphs

We report a study of polymorphic boron nitride (BN) samples. We interpret the photoluminescence (PL) line at $6.032\ifmmode\pm\else\textpm\fi{}0.005\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ that can be recorded at 8 K in $s{p}^{2}$-bonded BN as being the signature of the excitonic fundamental bandgap of the Bernal BN (bBN) [or graphitic BN (gBN)] polymorph. This is determined by advanced PL measurements combined with x-ray characterizations on pure hexagonal BN (hBN) and on polymorphic crystal samples, later compared with the theoretical predictions of Sponza et al., [Phys. Rev. B 98, 125206 (2018)]. The overall picture is consistent with a direct excitonic fundamental bandgap of the bBN (or gBN) polymorph. This value $d{X}_{b}=6.032\ifmmode\pm\else\textpm\fi{}0.005\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ is higher than the indirect bandgap of hBN $(i{X}_{h}=5.955\ifmmode\pm\else\textpm\fi{}0.005\phantom{\rule{0.16em}{0ex}}\mathrm{eV})$.

Four superhard sp3 hybrid cubic boron nitride polymorphs: A first principles calculations

In this study, four sp3 hybrid boron nitride polymorphs were proposed based on first principles calculations. The calculation results indicated that, at ambient conditions, four polymorphs are stable based on the criteria of dynamic and mechanical stability. At ambient conditions, they are thermodynamically metastable than h-BN, but more stable under high pressure conditions. In these four boron nitride phases, atoms are assembled in cubic symmetry, which are all sp3 hybrid cubic diamond-like structures, and the results showed that the Vickers hardness of them are as hard as c-BN, indicating they are potential superhard materials. Meanwhile, these four structures are considered as wide band gap semiconductor structures with direct band gap. Therefore, these four boron nitride structures have great potential as photovoltaic electronic devices and cutting tools.

Three metallic BN polymorphs: 1D multi-threaded conduction in a 3D network.

In this paper, three novel metallic sp2/sp3-hybridized boron nitride (BN) polymorphs are proposed by first-principles calculations. One of them, denoted as tP-BN, is predicted based on the evolutionary particle swarm structural search. tP-BN is composed of two interlocked rings forming a tube-like 3D network. The stability and band structure calculations show that tP-BN is metastable and metallic at zero pressure. Calculations for the density of states and electron orbitals confirm that the metallicity originates from the sp2-hybridized B and N atoms, forming 1D linear conductive channels in the 3D network. According to the relationship between the atomic structure and electronic properties, another two 3D metastable metallic sp2/sp3-hybridized BN structures are constructed manually. Electronic property calculations show that both of these structures have 1D conductive channels along different axes. The polymorphs predicted in this study enrich the structures and provide a different picture of the conductive mechanism of BN compounds.

Structure and electronic properties of 4-8 and 4-6-12 layered varieties of boron nitride

The structure of two new layered polymorphic varieties of boron nitride was calculated by the density functional theory method using the gradient approximation. The structure of layers BN-L4-8 and BN-L4-6-12 differs from the structure of the hexagonal layer of boron nitride in that their surface is formed not only from hexagons. As a result of the calculations, it was found that the sublimation energy of the new layers (17.36 and 17.14 eV (BN)-1 for the layers BN-L4-8 and BN-L4-6-12, respectively) is less than the sublimation energy of hexagonal boron nitride ( 18.14 eV (BN)-1). The band gap of new boron nitride polymorphs is about 3.9 eV, which is less than the calculated width of the band gap in BN-L6 – 4.69 eV.

Crystal Structure Exploration of Boron Nitride Polymorphs Using Anharmonic Downward Distortion Following Method with Potential Energy Surface Modified by the Inverse of Lattice Volume

The boron nitride polymorphs were explored using the anharmonic downward distortion following (ADDF) method with the energy value of the density functional-based tight binding approximation modified by the inverse of the volume of a unit cell. Twelve novel boron nitride polymorphs were discovered. Previously, it has been difficult to search reaction pathways connecting two-dimensional structures such as hexagonal boron nitride to three-dimensional structures using the ADDF method. This problem was partially resolved using this approach.

Direct and indirect excitons in boron nitride polymorphs: A story of atomic configuration and electronic correlation

We compute and discuss the electronic band structure and excitonic dispersion of hexagonal boron nitride (hBN) in the single layer configuration and in three bulk polymorphs (usual AA' stacking, Bernal AB, and rhombohedral ABC). We focus on the changes in the electronic band structure and the exciton dispersion induced by the atomic configuration and the electron-hole interaction. Calculations are carried out on the level of \textit{ab initio} many-body perturbation theory (GW and Bethe Salpeter equation) and by means of an appropriate tight-binding model. We confirm the change from direct to indirect electronic gap when going from single layer to bulk systems and we give a detailed account of its origin by comparing the effect of different stacking sequences. We emphasize that the inclusion of the electron-hole interaction is crucial for the correct description of the momentum-dependent dispersion of the excitations. It flattens the exciton dispersion with respect to the one obtained from the dispersion of excitations in the independent-particle picture. In the AB stacking this effect is particularly important as the lowest-lying exciton is predicted to be direct despite the indirect electronic band gap.

Structural impact on the eigenenergy renormalization for carbon and silicon allotropes and boron nitride polymorphs

The phonon-induced renormalization of electronic band structures is investigated through first-principles calculations based on the density functional perturbation theory for nine materials with various crystal symmetries. Our results demonstrate that the magnitude of the zero-point renormalization (ZPR) of the electronic band structure is dependent on both crystal structure and material composition. We have performed analysis of the electron-phonon-coupling--induced renormalization for two silicon (Si) allotropes, three carbon (C) allotropes, and four boron nitride (BN) polymorphs. Phonon dispersions of each material were computed, and our analysis indicates that materials with optical phonons at higher maximum frequencies, such as graphite and hexagonal BN, have larger absolute ZPRs, with the exception of graphene, which has a considerably smaller ZPR despite having phonon frequencies in the same range as graphite. Depending on the structure and material, renormalizations can be comparable to the GW many-body corrections to Kohn-Sham eigenenergies and, thus, need to be considered in electronic structure calculations. The temperature dependence of the renormalizations is also considered, and in all materials, the eigenenergy renormalization at the band gap and around the Fermi level increases with increasing temperature.

Publisher's Note: Hole polarons and p -type doping in boron nitride polymorphs [Phys. Rev. B 96 , 100102(R) (2017)

Publisher's Note: Hole polarons and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>p</mml:mi></mml:math> -type doping in boron nitride polymorphs [Phys. Rev. B <b>96</b> , 100102(R) (2017)

Hole polarons and p -type doping in boron nitride polymorphs

Boron nitride polymorphs hold great promise for integration into electronic and optoelectronic devices requiring ultrawide band gaps. We use first-principles calculations to examine the prospects for $p$-type doping of hexagonal ($h\ensuremath{-}\mathrm{BN}$), wurtzite ($wz\ensuremath{-}\mathrm{BN}$), and cubic ($c\ensuremath{-}\mathrm{BN}$) boron nitride. Group-IV elements (C, Si) substituting on the N site result in a deep acceptor, as the atomic levels of the impurity species lie above the BN valence-band maximum. On the other hand, group-II elements (Be, Mg) substituting on the B site do not give impurity states in the band gap; however, these dopants lead to the formation of small hole polarons. The tendency for polaron formation is far more pronounced in $h\ensuremath{-}\mathrm{BN}$ compared to $wz\ensuremath{-}\mathrm{BN}$ or $c\ensuremath{-}\mathrm{BN}$. Despite forming small hole polarons, Be acceptors enable $p$-type doping, with ionization energies of 0.31 eV for $wz\ensuremath{-}\mathrm{BN}$ and 0.24 eV for $c\ensuremath{-}\mathrm{BN}$; these values are comparable to the Mg ionization energy in GaN.