Crystal structures and formation mechanisms of boron-rich tungsten borides

Gu, Chao; Liang, Yongcheng; Zhou, Xuefeng; Chen, Jian; Ma, Dejiang; Qin, Jiaqian; Zhang, Wenqing; Zhang, Qiang; Daemen, Luke L.; Zhao, Yusheng; Wang, Shanmin

doi:10.1103/physrevb.104.014110

Cited by 10 publications

(11 citation statements)

References 58 publications

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“…Similar behaviors have been reported in other systems. For example, transition-metal carbonitrides have the largest elastic constant C 44 at a VEC of 8.4 e/f.u., , and the AlB 2 -type diborides exhibit the lowest formation energy at a VEC of 10 e/f.u. , …”

Section: Resultssupporting

confidence: 76%

“…For example, transition-metal carbonitrides have the largest elastic constant C 44 at a VEC of 8.4 e/f.u., 23,24 and the AlB 2 -type diborides exhibit the lowest formation energy at a VEC of 10 e/f.u. 29,30 For Re 0.5 W 0.5 C, the VEC is 10.5 e/f.u. Although the pd bonding states are fully occupied, the dd bonding states and pd antibonding states are partially filled, which is responsible for its relatively low shear stiffness and hardness.…”

Section: ■ Results and Discussionsupporting

confidence: 68%

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Vacancy Hardening and Ordering in Rhenium Tungsten Carbides

et al. 2022

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Vacancies generally reduce the number of chemical bonds and hence cause structural softening. It is puzzling, however, that substoichiometric Re0.5W0.5C0.4 with 60% carbon vacancies was identified as a superhard material. Here, we report the underlying mechanism responsible for such anomalous vacancy-induced hardening in the Re0.5W0.5C1–x system via first-principles calculations. The shear stiffness and hardness increase consistently with rising carbon vacancy concentration in Re0.5W0.5C1–x and reach the maximum at about x = 40%. Such an unexpected hardening phenomenon originates from a gradual relief of the shear-unstable dd bonding and unfavorable pd antibonding interactions owing to the formation of C-vacancies. We further predict that the simultaneous ordered vacancies of W and C atoms can produce a cubic crystalline Re2/3W1/3C that is isomorphic with the NbO type. The calculations on vibrational, mechanical, and electronic properties reveal that this phase has considerable structural stability and is a hard metallic material. This work not only elucidates the intriguing mechanism responsible for the vacancy hardening in this class of systems but also provides a new principle for the structural stability of other transition-metal compounds.

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Section: Resultssupporting

confidence: 76%

Section: ■ Results and Discussionsupporting

confidence: 68%

Vacancy Hardening and Ordering in Rhenium Tungsten Carbides

et al. 2022

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“…Single-crystal electron diffraction (SED) pattern in Figure 6f is obtained by a fast Fourier transform (FFT) of a selected area of TEM image (Figure S4b), which is consistent with the pattern simulated using the WB 2.34 structural model as determined in our recent work (Figure 6g). 44 Obviously, our current high-P reaction route can readily synthesize high-quality phase-pure WB 2+x powders with tunable grain size, which may be favorable for many applications such as catalysts where the nanoparticles with a high-surface area are required. Besides, the high-T products of our method are single-crystal forms (Figures 6h and S4c), in stark contrast to the polycrystalline bulk sample prepared by traditional methods from the reaction between W and B powders (Figure 6i,j).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Along the [100] crystallographic direction, the W–W bilayers can be identified in Figure e. Single-crystal electron diffraction (SED) pattern in Figure f is obtained by a fast Fourier transform (FFT) of a selected area of TEM image (Figure S4b), which is consistent with the pattern simulated using the WB 2.34 structural model as determined in our recent work (Figure g) . Obviously, our current high- P reaction route can readily synthesize high-quality phase-pure WB 2+ x powders with tunable grain size, which may be favorable for many applications such as catalysts where the nanoparticles with a high-surface area are required.…”

Section: Resultsmentioning

confidence: 99%

Synthesis, Phase Evolutions, and Stabilities of Boron-Rich Tungsten Borides at High Pressure

Zhou

et al. 2022

Inorg. Chem.

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Boron-rich tungsten borides such as WB2+x and WB3+x have been highly expected to be superhard with many advantages over conventional superhard materials. However, because the formation of boron-rich tungsten borides is thermodynamically unfavorable at ambient pressure, their crystal structures, compositions, and properties are largely unexplored, which have impeded the rational design of functional materials in the W–B family. In this work, using unique high-pressure reactions, we report a systematic synthesis study of challenging compounds of tungsten borides including WB, WB2+x , and WB3+x . The use of pressure, combined with the controllable temperature, heating duration, and ratios of starting reactants, leads to different compositions and structures of final products with largely tunable crystallite size from nanocrystalline to single-crystal forms. In addition, the optimal conditions for the formation of WB3+x are well investigated by tuning the temperature and starting ratio of reactants, as well as by adding a solvent material. Phase diagrams and stabilities of the involved W–B compounds are also well depicted, which would provide an important guidance for future exploratory synthesis and study of the family of transition-metal borides.

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“…29–37 Among them, a phase referred to as “WB 4 ”, 38–49 and its several derivatives ( e.g. , W 1− x B 3 , WB 4− x , WB 4+ x , WB 4.2 , and WB 5− x ) 50–56 were identified as highly promising candidates, whose mechanical characteristics ( e.g. theoretical and experimental values of H V vary from 30 to 45 GPa (ref.…”

Section: Introductionmentioning

confidence: 99%