Crystal structure of ω-Al₄Cr

Abstract

The new polymorph of tetraaluminium chromium, Al4Cr, designated as the ω-phase, was obtained as the product from a high-pressure sintering (HPS) process of a stoichiometric Al4Cr mixture. The crystal structure is isotypic with Al4Mo and Al4W. The unit cell of ω-Al4Cr is much smaller than any of the other reported Al4Cr polymorphs, containing 30 rather than several hundred atoms.

On the exploration of the melting behavior of metallic compounds and solid solutions via multiple classical molecular dynamics approaches: application to Al-based systems

“…Contrary to all the Al 3 Zr ordered compounds presented in Section 3.2.1, the melting temperature of the Al 4 Cr intermetallic is not much impacted by the introduction of vacancies in its perfect structure. The melting temperature of the perfect lattice is lower than with vacancies, this is because the ω-phase 71 is unstable and the presence of vacancies allows it to restructure itself. This was confirmed with additional tests on the Al 4 W structure (Materials Project id-30336) using the Al–Cr potential, which did not display this behavior.…”

“…Additionally, we controlled the local chemical ordering surrounding a vacancy in multicomponent systems to study its impact on the energetic stability of the solid structure. The following list of structures were studied in our work via the void method: (1) pure metals (unary systems): FCC-aluminum (2) binary intermetallic compounds: Al 3 Zr (L1 2 , D0 23 ordered structures and FCC disordered phase), the ω-phase Al 4 Cr, 71 B32-AlLi and (3) disordered binary solid solutions: Al–Zn FCC-disordered (90 at% Al). The results of the void method were systematically compared to those obtained using the interface method in pure systems.…”

“…3.2.2 Peritectic melting intermetallic: Al 4 Cr. According to the work of Fan, 71,98 the o-Al 4 Cr phase is the most stable Al 4 Cr phase at high pressure, transitioning from the m-phase, a peritectically melting intermetallic. 98,99 This stability was found to allow the structure to accept the presence of defects.…”

“…98,99 This stability was found to allow the structure to accept the presence of defects. 71 Fig. 9 shows the evolution of the melting temperature of this compound as a function of the concentration of vacancies.…”

“…For the congruently melting scenario, the Al 3 Zr intermetallic is explored in its stable form (D0 23 ) and with two metastable configurations (L1 2 and disordered FCC phase). For the case of a peritectic intermetallic's melting, the ω-Al 4 Cr 71 compound is examined. The importance of the site distribution (using the vacancy method) to activate the melting process is represented through the modeling of the AlLi (B32) phase, which is an ordered solution with a wide solubility range according to classical thermodynamics.…”