Thermodynamic and mechanical stabilities of α- and β-Ta4AlC3 via first-principles investigations.

Recently, it has been predicted that Ta4AlC3 is likely to exhibit an (α-β) polymorphic transformation at temperatures above 1873 K. However, recent X-ray diffraction and transmission electron microscopy experiments suggest on the other hand that the α phase remains stable up to temperatures close to the limit of experimental capabilities and no transition has yet been observed. While the matter has already been settled experimentally, in this work, we re-investigate the phase stability problem in Ta4AlC3 by using first-principles methods. The study was carried out by considering both thermodynamic and mechanical stabilities of the Ta4AlC3 polymorphs. Particularly, finite-temperature Gibbs free energies and elastic properties of the polymorphs were calculated using density functional theory. Calculation results reveal that the α phase continue to be stable even at temperatures exceeding 1875 K, which is in agreement with experimental results reported in literature. [ABSTRACT FROM AUTHOR]