(Al,Mg)₃La: a new phase in the Mg-Al-La system

Area of Science:

• Materials Science
• Crystallography
• Solid-State Chemistry

Background:

• The Mg-Al-La system is crucial for understanding intermetallic compound formation.
• Binary phases like Al₃La provide a basis for ternary system investigations.
• Exploring Mg-rich compositions can reveal novel structural phases.

Purpose of the Study:

• To identify and characterize new ternary phases in the Mg-rich Mg-Al-La system.
• To determine the crystal structure of the newly discovered (Al,Mg)₃La phase.
• To compare the structure of the ternary phase with its binary counterpart.

Main Methods:

• Conventional X-ray powder diffraction (XRD) for initial phase identification.
• Transmission electron microscopy (TEM) for structural analysis.
• High-resolution XRD for precise crystal structure refinement.
• High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) for structural verification.

Main Results:

• A new ternary phase, (Al,Mg)₃La, was identified in the Mg-rich Mg-Al-La system.
• The crystal structure was determined to be orthorhombic with space group C222₁.
• Lattice parameters were refined as a = 4.3365(1) Å, b = 18.8674(4) Å, and c = 4.4242(1) Å.
• The determined structure is significantly different from the binary Al₃La phase (P6₃/mmc).

Conclusions:

• The discovery of the (Al,Mg)₃La phase expands the known phase diagram of the Mg-Al-La system.
• The unique orthorhombic structure highlights the influence of magnesium on the crystal lattice.
• Further research can explore the properties and potential applications of this new ternary phase.