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• Calorimetry and X-ray powder diffraction data for (Li,Na)acetate salts. • The Li 1- x Na x CH 3 COO phase diagram has a eutectic at x = 0.55. • Li 4 Na(CH 3 COO) 5 and LiNa 3 (CH 3 COO) 4 compounds give rise to peritectic reactions. • Quenched samples with x <0.55 are glasses that crystallize when heated. • Samples with x >0.55 are mixtures of glass and crystals. Anhydrous mixtures of lithium acetate and sodium acetate were investigated by differential scanning calorimetry and X-ray powder diffraction. A tentative phase diagram is derived from these data. The Li 1- x Na x CH 3 COO system has a eutectic for the NaCH 3 COO molar fraction of x ≈ 0.55. The relatively low eutectic melting point at 448 K (175 ∘ C) may make this composition an interesting molten salt solvent. Peritectic reactions correspond to phases with compositions near Li 4 Na(CH 3 COO) 5 and LiNa 3 (CH 3 COO) 4. On the Li-rich side of the eutectic, the system, prepared as a glass, can crystallized deliberately. This allows checking the data validity with the first law of thermodynamics. The stability range of the supercooled liquid increases with x up to Li 0.55 Na 0.45 CH 3 COO. For higher sodium concentrations, the samples remain mixtures of glass and crystalline phases, with the amount of the vitreous component decreasing linearly from x = 0.45 to x = 1. The fragility of the liquid state, highest for pure LiCH 3 COO, decreases by a factor of two over the range 0 < x < 0.2 , and remains constant for higher x. [ABSTRACT FROM AUTHOR]