Lattice stability of aluminum-rare earth binary systems: A first-principles approach

The thermodynamics of over 330 compounds in 15 Al-RE (RE=rare earth elements) binary systems is studied via first-principles density-functional theory at low-temperature limit. The calculated phase stabilities at T=0 K are in very good agreement with experimentally reported ones for the majority of the systems. For example, we show the Al₂RE.cF24 structure is the most stable compound phase in each binary and it indeed has the highest (congruent) melting point in each system. In some other cases, we obtain results previously unknown experimentally. For example, we suggest that the structure of the observed compound AlTm₂ is isostructural with Co₂Si.oP12 (prototype Co₂Si, Pearson symbol oP12), we confirm the stability of AlEu.oP20 rather than AlEu.oP18 by examining the energetics of vacancy substitution, and we predict the unreported Al-Pm phase diagram. Relative accuracy of different potentials and calculational details are addressed. This study predicts that the Al-RE phase diagrams evolve systematically across the entire RE series, interrupted by anomalies at elements Ce and especially Eu and Yb. Trends in lattice stability across the RE series are explained on the basis of interatomic bonding and strain. This study demonstrates that first-principles calculations can be employed to (1) further examine and improve the experimentally established binary-alloy phase diagrams, and (2) provide accurate enthalpy data for stable and hypothetical compounds and structures.