Searching for Missing Binary Equiatomic Phases: Complex Crystal Chemistry in the Hf-In System

Area of Science:

• Materials Science
• Crystallography
• Computational Materials Science

Background:

• Many binary equiatomic phases (AB) remain experimentally unconfirmed.
• Machine learning models predict the Hf-In system to form a CuAu-type structure.

Purpose of the Study:

• To experimentally investigate the Hf-In system and verify the predicted CuAu-type structure.
• To determine the crystal structure of the Hf-In binary phase.

Main Methods:

• High-temperature reaction of Hafnium (Hf) and Indium (In) elements at 1070 K.
• Energy-dispersive X-ray analysis for composition determination.
• Powder and single-crystal X-ray diffraction for structure solution.

Main Results:

• Two distinct crystalline phases were identified in the Hf-In sample.
• The bulk phase adopted the γ-brass (Cu5Zn8) type structure (space group I4̅3 m).
• The surface crystals exhibited the CuPt7 type structure (space group Fm3̅ m).

Conclusions:

• The experimentally determined γ-brass-type structure of bulk HfIn is a distorted variant of the predicted CuAu-type structure.
• Structural relationships explain the discrepancy between predicted and observed phases.
• This study resolves the structural ambiguity for the Hf-In system.