Revealing the Unusual Boron-Pinned Layered Substructure in Superconducting Hard Molybdenum Semiboride

Area of Science:

• Materials Science
• Solid State Physics
• Superconductivity

Background:

• Improving electrical conductivity in hard materials is crucial for their technological applications.
• Molybdenum borides (MoB, MoB2) are known hard materials, but their conductivity can be limiting.
• Understanding the relationship between composition, structure, and properties is key for designing advanced materials.

Purpose of the Study:

• To synthesize and characterize a novel high-hardness metallic molybdenum boride (Mo2B).
• To investigate the electrical conductivity and superconductivity of Mo2B.
• To elucidate the relationship between boron concentration, mechanical hardness, and electronic properties.

Main Methods:

• High-pressure and high-temperature synthesis methods were employed to produce Mo2B.
• Temperature-dependent electrical resistivity measurements were conducted to assess conductivity and superconductivity.
• Vickers hardness testing was performed to quantify mechanical properties.
• First-principles calculations were utilized to understand the underlying mechanisms of hardness.

Main Results:

• High-hardness metallic Mo2B was successfully synthesized.
• Mo2B exhibits excellent metallic conductivity and weak-coupled superconductivity with a critical temperature (Tc) of 6.0 K.
• The Vickers hardness of Mo2B reached 16.5 GPa, surpassing that of MoB and MoB2.
• Mechanical properties are optimized by a specific boron concentration, not necessarily a high one.
• First-principles calculations indicate that the pinning effect of light elements, like boron, is directly related to hardness.

Conclusions:

• The metal-rich molybdenum semiboride, Mo2B, presents a promising combination of high hardness and excellent electrical conductivity.
• The findings suggest that designing high-hardness conductive materials should focus on the structural arrangement of light elements, such as boron's pinning effect in layered structures, rather than solely on high elemental concentrations.
• Mo2B's superconductivity at 6.0 K opens avenues for research in superconducting hard materials.