Gibbs energies of formation of CoF
2 and MnF
2 have been measured in the temperature range from 700 to 1100 K using Al
2O
3-dispersed CaF
2 solid electrolyte and Ni+NiF
2 as the reference electrode. The dispersed solid electrolyte has higher conductivity than pure CaF
2 thus permitting accurate measurements at lower temperatures. However, to prevent reaction between Al
2O
3 in the solid electrolyte and NiF
2 (or CoF
2) at the electrode, the dispersed solid electrolyte was coated with pure CaF
2, thus creating a composite structure. The free energies of formation of CoF
2 and MnF
2 are (± 1700) J mol
−1; {fx37-1} The third law analysis gives the enthalpy of formation of solid CoF
2 as Δ
H° (298·15 K) = −672·69 (± 0·1) kJ mol
−1, which compares with a value of −671·5 (± 4) kJ mol
−1 given in Janaf tables. For solid MnF
2, Δ
H°(298·15 K) = − 854·97 (± 0·13) kJ mol
−1, which is significantly different from a value of −803·3 kJ mol
−1 given in the compilation by Barin
et al.
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