The solid-phase portion of the Al-Li phase diagram has been computed from first principles both at zero pressure and at a hydrostatic compression of 5.4 GPa. Computation of the pressure dependence of the Al-Li phase equilibria answers two questions: (1) how important is the effect of the atomic size difference, and (2) is the stability of the ${\mathrm{Al}}_3$Li precipitates influenced by high hydrostatic stress. The zero-pressure first-principles phase diagram exhibits excellent qualitative agreement with experimental data. The presence or absence of solid solutions (SS), of stable and metastable intermetallic phases, and their degree of order are computed correctly. Compression is predicted to affect the phase equilibria in Al-Li as follows: (1) the solubility of Li in fcc Al-rich SS is decreased, (2) the solubility of Al in Li is increased. However, the low melting point of Li limits the range of SS, and (3) the metastable ${\mathrm{Al}}_3$Li Al-rich fcc SS phase equilibrium is unaffected and the stability of the precipitates is unchanged, (4) the ordering tendencies at Li-rich compositions are slightly enhanced. Although high pressure eliminates the difference in atomic volume of the pure constituents, it has almost no effect on the solid-solid phase equilibria in this alloy system. A simple method for verifying the accuracy of the cluster expansion for the configurational internal energy is presented and applied. Moreover, it has been shown that with a convenient choice of the occupation numbers, one can define correlation functions which greatly facilitate the determination of new ground state structures. © 1996 The American Physical Society.

• Received 10 October 1995

DOI:https://doi.org/10.1103/PhysRevB.53.6137