First-Principles Calculation of the Cu-Li Phase Diagram

Abstact We present first-principles calculations of the solid-state portion of the Cu-Li phase diagram based on the cluster expansion formalism coupled with the use of (i) bond length-dependent transferable force constants and lattice dynamics calculations to model of vibrational disorder and (ii) lattice gas Monte Carlo simulations to model configurational disorder. These calculations help settle the existence of additional phases in the Cu-Li phase diagram that have been postulated, but not yet clearly established. Our calculations predict the presence of at least one additional phase and the associated predicted phase transitions are consistent with our electrochemical measurements, which exhibit clear plateaus in the electromotive force-composition curve. In 1976, Smith and Moser [1] published the thermodynamic assessments of binary lithium alloys using information from the literature, followed by experimental investigations by galvanic cells initiated at the Institute of Metallurgy and Materials Sciences in Kraków in 1981 in cooperation with the University of Saarland in Germany. The following binary systems were studied: [11]. These studies were extended later to ternary Al-Li-Mg alloys including calorimetric measurements in cooperation with the Max Planck Institute in Stuttgart [12] and to phase diagram calculations of Al-Li-Mg [13] and on Al-Li-Cu [14] systems. In 1998 [14] during the Thermodynamics of Alloys Conference, thermodynamic studies of solid Cu-Li alloys from electromotive force (emf) measurements were presented that suggested the existence of intermetallic phases. Previous phase diagram assessments of Pelton [15] and of Saunders [16] do not indicate the existence of intermetallic phases. In 1996, Borgstedt and Gumiński [17] performed a critical evaluation of previous phase diagram assessments. They indicated that the only experimental thermodynamic data of enthalpies of mixing [18] of liquid alloys based on Cu exhibiting slight exothermic effect (-1.1 kJ/mol) suggests negative deviations from ideal behavior. In addition, taking into account results of Kraus et al. [19] and Old et al.[20] who suggested the formation of Cu 4 Li phase, probably formed at the temperature 473-873 K, Borgstedt and Gumiński [17] introduced this phase into a schematic phase diagram of the Cu-Li system based on Pelton's [15] assessment. It should be noted that estimates of enthalpy of mixing by Miedema et al. [21] yield a much more exothermic effect for the Cu-Li system amounting to –39 kJ/mol. In this article, we employ first-principles calculations in conjunction with electrochemical measurements to investigate the presence of intermetallic phases in the Cu-Li system. Our findings suggest that the only …