First‐Principles Investigation on the Chemical Bonding and Intrinsic Elastic Properties of Transition Metal Diborides TMB
            <sub>2</sub>
            (TM=Zr, Hf, Nb, Ta, and Y)

Zhou, Yanchun; Wang, Jiemin; Li, Zhen; Zhan, Xun; Wang, Jingyang

doi:10.1002/9781118700853.ch4

Cited by 10 publications

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“…The TM diborides have a complex mix of bond types resulting in a remarkable combination of metal-like and ceramic-like properties. [22][23][24][25] The AlB2 structure consists of layers of close-packed metal atoms that alternate with boron in graphite-like sheets. Metallic bonding in the TM layers leads to high electrical (10 7 S/m for ZrB2) 26,27 and thermal (~130 W/m•K for ZrB2) [27][28][29] conductivities, while strong covalent bonding in the B layers gives high hardness (~33 GPa for TiB2) 30 and elastic modulus (~560 GPa for TiB2) 31 values.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of ultra-refractory transition metal diboride compounds

2016

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Section: Introductionmentioning

confidence: 99%

Synthesis of ultra-refractory transition metal diboride compounds

2016

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“…In the ZrB 2 and HfB 2 scenarios, the high Young's modulus is underpinned by the strong covalent bonds between B atoms in the crystal structure. [6,7] It is well established that, in addition to chemical composition, chemical bonding plays an important role in dictating the structure and properties of a material. Therefore, comparing to chemical composition modification of ZrB 2 (or HfB 2 ), modification of the nature of chemical bonding in transition metal borides is more effective in *Corresponding author.…”

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“…The finite states at a Fermi level are from both Y 3d and B 2p states, indicating the presence of the metallic bond in YB 6 and it is electrically conductive. In short, metallic, ionic and covalent bonding all have contributions to the chemical bonding in YB 6 .…”

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“…In addition, YB 6 has Young's modulus of 156 GPa, which is much lower than those of ZrB 2 and HfB 2 (523 and 535 GPa, respectively). [46] Low Young's modulus indicates better thermal shock resistance for YB 6 .…”

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“…Crystal structure and electron density map on the (002) plane. (a) A 2 × 1 × 1 cell of MB6 showing octahedron within the unit cell and the inter-octahedral B-B bonds connecting the B 6 octahedra into the three-dimensional network. (b) Electron density difference map on the (002) plane across the B atoms, the B 6 octahedron is cut into a two-dimensional B 4 square.…”

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YB₆: A ‘Ductile’ and Soft Ceramic with Strong Heterogeneous Chemical Bonding for Ultrahigh-Temperature Applications

Zhou

Liu

Xiang

et al. 2015

Materials Research Letters

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Transition metal borides have contributed to the success of ultrahigh-temperature materials (UHTM) development. Current ZrB 2and HfB 2-based UHTMs exhibit high-temperature environmental stability, high strength and modulus but inevitable brittleness due to strong covalent bonding. In contrast but interestingly, YB 6 is predicted as a 'ductile' and soft ceramic for ultrahigh-temperature applications, through density functional theory investigations on its electronic structure and bonding properties. The 'ductility' is underpinned by chemical bonding anisotropy, that is, a strong σ bond connecting the B 6 octahedra and a weak banana bond formed by overlapping the lobes of two perpendicular p orbitals (τ bond).

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Ab Initio Prediction of Mechanical and Electronic Properties of Ultrahigh Temperature High‐Entropy Ceramics (Hf_0.2Zr_0.2Ta_0.2M_0.2Ti_0.2)B₂ (M = Nb, Mo, Cr)

Wang

Gan

Wang

et al. 2018

Physica Status Solidi (b)

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High-entropy metal diborides (Hf 0.2 Zr 0.2 Ta 0.2 M 0.2 Ti 0.2 )B 2 (M ¼ Nb, Mo, Cr) are a new class of ultrahigh temperature ceramics. The novel structural, mechanical, and electronic properties of (Hf 0.2 Zr 0.2 Ta 0.2 M 0.2 Ti 0.2 )B 2 (M ¼ Nb, Mo, Cr) are studied within density functional theory, with the compositional disorder being treated using the special quasi-random structures technique. The elastic stiffness constants C ij , as well as bulk, shear and Young's modulus of (Hf 0.2 Zr 0.2 Ta 0.2 M 0.2 Ti 0.2 )B 2 (M ¼ Nb, Mo, Cr) are studied to estimate the mechanical properties. The ductility is also investigated from several criterions, showing that (Hf 0.2 Zr 0.2 Ta 0.2 M 0.2 Ti 0.2 )B 2 (M ¼ Nb, Mo, Cr) is still intrinsically brittle. The high Debye temperature of (Hf 0.2 Zr 0.2 Ta 0.2 M 0.2 Ti 0.2 )B 2 (M ¼ Nb, Mo, Cr) indicates the strong interatomic interactions and good thermal conductivity. The detailed investigations of electronic structure reveal that covalent and metallic bonds are respectively formed in the boron layer and the metal layer, mixed ionic and covalent bonds are formed between the metals and boron interlayer.

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First‐Principles Investigation on the Chemical Bonding and Intrinsic Elastic Properties of Transition Metal Diborides TMB ₂ (TM=Zr, Hf, Nb, Ta, and Y)

Cited by 10 publications

References 31 publications

Synthesis of ultra-refractory transition metal diboride compounds

Synthesis of ultra-refractory transition metal diboride compounds

YB₆: A ‘Ductile’ and Soft Ceramic with Strong Heterogeneous Chemical Bonding for Ultrahigh-Temperature Applications

Ab Initio Prediction of Mechanical and Electronic Properties of Ultrahigh Temperature High‐Entropy Ceramics (Hf_0.2Zr_0.2Ta_0.2M_0.2Ti_0.2)B₂ (M = Nb, Mo, Cr)

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First‐Principles Investigation on the Chemical Bonding and Intrinsic Elastic Properties of Transition Metal Diborides TMB 2 (TM=Zr, Hf, Nb, Ta, and Y)

Cited by 10 publications

References 31 publications

Synthesis of ultra-refractory transition metal diboride compounds

Synthesis of ultra-refractory transition metal diboride compounds

YB6: A ‘Ductile’ and Soft Ceramic with Strong Heterogeneous Chemical Bonding for Ultrahigh-Temperature Applications

Ab Initio Prediction of Mechanical and Electronic Properties of Ultrahigh Temperature High‐Entropy Ceramics (Hf0.2Zr0.2Ta0.2M0.2Ti0.2)B2 (M = Nb, Mo, Cr)

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First‐Principles Investigation on the Chemical Bonding and Intrinsic Elastic Properties of Transition Metal Diborides TMB ₂ (TM=Zr, Hf, Nb, Ta, and Y)

YB₆: A ‘Ductile’ and Soft Ceramic with Strong Heterogeneous Chemical Bonding for Ultrahigh-Temperature Applications

Ab Initio Prediction of Mechanical and Electronic Properties of Ultrahigh Temperature High‐Entropy Ceramics (Hf_0.2Zr_0.2Ta_0.2M_0.2Ti_0.2)B₂ (M = Nb, Mo, Cr)