Crystal Structure, Microstructure and Electronic Properties of a Newly Discovered Ternary Phase in the Al-Cr-Sc System

• Published in: Crystals (Basel) Vol. 11; no. 12; p. 1535
• Main Authors: Kušter, Monika, Meden, Anton, Markoli, Boštjan, Samardžija, Zoran, Vončina, Maja, Boulet, Pascal, Gaudry, Émilie, Dubois, Jean-Marie, Šturm, Sašo
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.12.2021; MDPI
• Series: This article belongs to the Special Issue Crystallography of Structural Phase Transformations (Volume II)
• Subjects: Al-Cr-Sc system; Alloying; Alloys; Aluminum; Binary alloys; Chemical Sciences; Cristallography; Crystal structure; crystal structure refinement; Crystallography; Density functional theory; Density of states; Electric arc melting; Electronic properties; Electronic structure; First principles; HAADF-STEM; High temperature; Investigations; Laves phase; Material chemistry; Microstructure; Occupancy; Scandium; Scanning electron microscopy; Scanning transmission electron microscopy; Single crystals; Software; Ternary systems; Transmission electron microscopy; Unit cell; X ray powder diffraction; X-ray diffraction; Germany; HAADF-STEM; Al-Cr-Sc system; Laves phase; crystal structure refinement
• ISSN: 2073-4352; 2073-4352
• DOI: 10.3390/cryst11121535

This study focused on the crystal and electronic structures of a newly discovered phase in the Al-Cr-Sc system. The latter two species do not mix in a binary alloy, but can be alloyed with aluminium in the vicinity of the Al2−xCrxSc composition, where 0.3 < x < 0.5. After preparation of the pure constituents via arc melting, high-temperature annealing at 990 °C for 240 h was required to achieve full mixing of the elements. A detailed characterisation of the crystal structure, alloy microstructure and stability was obtained using single-crystal X-ray diffraction (SCXRD) and powder X-ray diffraction (PXRD), in addition to transmission electron microscopy (TEM), especially in high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) mode, scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDXS) and differential scanning calorimetry (DSC) measurements. The crystal structure was refined to a hexagonal unit cell of the MgZn2 type, space group no. 194, P63/mmc, which belongs to the Laves phases family. Special attention was paid to the occupancy of the crystallographic sites that were filled by both Cr and Al atoms. First-principles calculations based on the density functional theory (DFT) were performed to investigate the electronic structure of this ternary phase. The total density of states (DOS) exhibited a pronounced sp character, where a shallow pseudo-gap was visible 0.5 eV below the Fermi energy that brought a small but definite contribution to the thermodynamic stability of the compound.