THERMODYNAMIC PROPERTIES OF INTERMETALLIC SYSTEMS LITHIUM-ANTIMONY AND LITHIUM-BISMUTH

Galvanic cells of the type “LiAl,” Al|LiCl-KCl(e), 1|Li-X (X = Sb, Bi) were employed to determine the Gibbs free energy of formation (ΔGf°), and the corresponding enthalpies (ΔHf°), and entropies (ΔSf°) for the systems Li-Sb and Li-Bi as a function of composition from pure X to the Li-rich side of the Li3X phases. The Li/X ratio was changed systematically by use of the coulometric titration technique. ΔGf° values were obtained by integration of the coulometric titration curve from pure X to the composition of interest. Thermodynamic data have been determined for the trilithium compounds as a function of the stoichiometry. Δf° and ΔHf° were calculated from the temperature dependence of ΔGf°. Data were obtained over the temperature range 355°-600°C. At 400°C the following values were found for the standard Gibbs free energy of formation: −176.0 kJ mole−1 (Li2Sb), −260.1 kJ mole−1 (Li3Sb), −76.0 kJ mole−1 (LiBi), and −215.3 kJ mole−1 (Li3Bi), all ± 0.1 kJ mole−1. The standard enthalpies of formation are: −220.4 kJ mole−1 (Li2Sb), −325.2 kJ mole−1 (Li3Sb), −108.9 kJ mole−1 (LiBi), −293.5 kJ mole−1 (Li3Bi), all ± 0.7 kJ mole−1. The standard entropies of formation are: −66 J mole−1K−1 (Li2Sb), −97 J mole−1K−1 (Li3Sb), −49 J mole−1K−1 (LiBi), and −116 J mole−1K−1 (Li3Bi), all ± 1 J mole−1K−1. The experimental results were also used to examine the phase diagrams for Li-Sb and Li-Bi. The range of stoichiometry of Li3+δSb is very narrow (Δδ = 7 × 10−3), whereas Li3+δBi exhibits a large deviation from the ideal stoichiometry (Δδ = 0.22), predominantly on the lithium-deficit side. Li2Sb and LiBi have been found to be the only intermediate phases existing beside the trilithium phases in the temperature range investigated. © 1978, The Electrochemical Society, Inc. All rights reserved.