Al₄Ir: An Al-Ir Binary-Phase Superstructure of the Ni₂Al₃ Type

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• The Aluminum-Iridium (Al-Ir) system is crucial for understanding intermetallic compound formation.
• Investigating new binary phases can reveal novel material properties and structures.

Purpose of the Study:

• To discover and characterize a new binary phase in the Al-Ir system.
• To elucidate the crystal structure, stability, and electronic properties of the Al4Ir phase.

Main Methods:

• Single-crystal X-ray diffraction for structural determination.
• Scanning transmission electron microscopy (STEM) for atomic-scale imaging.
• Differential thermal analysis (DTA) for metastability assessment.
• Density functional theory (DFT) for electronic structure calculations.

Main Results:

• Discovery of a new Al4Ir binary phase crystallizing in the trigonal space group P3c1.
• Experimental confirmation of a supercell structure derived from Ni2Al3, attributed to Al atom ordering.
• Atomic-scale imaging revealed Al site misalignment causing the supercell.
• DTA confirmed the metastable nature of Al4Ir.
• DFT calculations supported experimental findings, indicating a metallic nature with electronic structure deviating from Hume-Rothery rules.

Conclusions:

• The Al4Ir phase represents a novel intermetallic compound in the Al-Ir system.
• Its metastability is linked to its unique electronic structure and atomic ordering.
• DFT analysis provides insights into bonding and stability, highlighting sp-d hybridization in Ir-centered clusters.