The Cu-Li-Sn phase diagram: Isothermal sections

Four isothermal sections in the Cu-Li-Sn phase diagram at 300 °C, 400 °C, 500 °C and 600 °C have been investigated by powder XRD of 108 samples, which are based on 60 alloy compositions annealed at different temperatures and quenched in cold water. Altogether 47 three-phase equilibria have been allocated experimentally to the isotherms. Besides the established two ternary compounds Li ₂CuSn (T1) and LiCu ₂Sn (T2), allocated in the hitherto known phase diagrams, four further ternary compounds could be proved. Their compositions are Li ₃Cu ₆Sn ₄ (T3), Li ₂CuSn ₂ (T4), Li ₃CuSn (T5) and Li ₆Cu ₂Sn ₃ (T6). There are hints to the existence of two additional ones with the estimated compositions Cu _0.12Li _0.66Sn _0.22 (T7) and Cu _0.11Li _0.65Sn _0.24 (T8). A new lithiation path of η′-Cu ₆Sn ₅ at room temperature was suggested, based on the appearance of ternary phases and phase equilibria along the section from η′-Cu ₆Sn ₅ to (Li): (η′-Cu ₆Sn ₅) → (η′-Cu ₆Sn ₅ + T3) → (T3) → (T3 + T4) → (T2 + T3 + T4) → (T2 + T4) → (T1 + T2 + T4) → (T1 + T4) → (T1) → ((Cu) + T1) → ((Cu) + T1 + T5) → ((Cu) + T5) → ((Cu) + T5 + Li ₁₇Sn ₄) → ((Cu) + Li ₁₇Sn ₄) → ((Cu) + (Li) + Li ₁₇Sn ₄) → ((Li) + Li ₁₇Sn ₄) → (Li).