Zero Thermal Expansion and Strong Covalent Binding of VB₂ Compound

Abstract

Zero thermal expansion (ZTE) is an intriguing phenomenon by virtue of its peculiar lack of expansion and contraction with temperature. The achievement of ZTE in a metallic material is a desired but challenging task. Here we report the ZTE behavior of a single-phase metallic VB2 compound, stacking with the V and B atomic layers along the c direction (α V = 2.18 × 10–6 K–1, 5–150 K). Neutron powder diffraction demonstrates that the ZTE behavior is entangled in the direct blocking of the lattice expansion along all crystallographic directions with temperature. X-ray photoelectron spectroscopy and density functional theory calculations indicate that strong covalent binding adheres the nearest-neighbor B–B and V–B pairs, which is proposed to control the ZTE within both the basal plane and the c direction. An intimate correlation is revealed between the covalent binding and the lattice parameters. Our work indicates the opportunity to design metallic ZTE with strong chemical binding in the future.

Switch of Thermal Expansions Triggered by Itinerant Electrons in Isostructural Metal Trifluorides

“…Materials with NTE are rare and could be categorized by diverse mechanisms, such as magnetic order in a FeNi Invar alloy, rare-earth intermetallic alloys, − MnM′Ge-based alloys (M′ = Co or Ni), , anti-perovskite nitrides, spontaneous polarization in PbTiO 3 -based ferroelectric solids, − strong covalent binding in VB 2 , chemical pressure, charge or orbital ordering in (Bi, La)­NiO 3 , Ca 2 RuO 4 , and V 2 OPO 4 , and so forth. Among them, NTE derived from soft optical phonons with negative Grüneisen parameters (γ) is a dominating branch, such as the prototype ZrW 2 O 8 , open-framework oxides, , cyanides, , metal–organic frameworks, and equally attractive cubic fluorides. − Owing to the critical role of soft optical phonons, to achieve MTE of open-framework solids, long-term cognition focuses on developing diverse chemical methods to mediate the specific phonon modes by introducing local structure distortion (LSD) in NTE materials.…”

Vanadium Diboride (VB2) for NO Electroreduction to NH3

“…The V 2p spectrum (Figure d) can be decomposed into two doublets of V 4+ –B (515.9.2/524.1 eV) and V 2+ –B (513.1/520.6 eV). Likewise, the deconvoluted B 1s spectrum (Figure e) shows the same V 4+ –B (192.3 eV) and V 2+ –B (188.5 eV) bonds, consistent with the reported VB 2 . − These results demonstrate the successful synthesis of VB 2 . In addition, electronic structure analysis reveals that VB 2 possesses a high-occupancy state near the Fermi level (Figure S1), together with a low work function of 4.397 eV (Figure S2), suggesting that VB 2 is metallically conductive, which is beneficial for boosting the electron transport to accelerate the reaction kinetics.…”