Ambient-pressure superconductivity in covalent Au-B frameworks stabilized by electropositive metals

Area of Science:

• Materials Science
• Solid-State Chemistry
• Superconductivity

Background:

• Extended covalent compounds involving gold are rare due to gold's preference for metallic or molecular coordination.
• Traditional chemical principles often limit the formation of gold-based covalent structures.

Purpose of the Study:

• To identify and characterize novel ternary compounds featuring gold-boron covalent frameworks.
• To explore the potential for superconductivity in these new materials.
• To demonstrate a new strategy for designing materials by overcoming electronegativity constraints.

Main Methods:

• High-pressure crystal structure search combined with first-principles calculations.
• Analysis of electronic structure and bonding configurations.
• Investigation of phonon-mediated superconductivity mechanisms.

Main Results:

• A family of ternary compounds, M₂AuB₆ (M = Na, K, Mg, Ca, Sr), with stable Au-B covalent frameworks was identified.
• A 'push-pull' design rule involving electropositive cations and electron-deficient boron octahedra was established.
• The Na₂AuB₆ and K₂AuB₆ phases exhibit superconductivity, with contributions from gold and boron electronic states and phonon interactions.
• Pressure-induced structures were successfully quenched to ambient pressure.

Conclusions:

• The M₂AuB₆ compounds represent a new class of materials with unique gold-boron covalent bonding.
• These compounds offer a viable platform for studying gold-based superconductivity.
• The electron-donor-guided materials discovery approach is effective for creating novel chemical structures and properties.