Thermodynamic studies on lithium ferrites

Thermodynamic studies on ternary oxides of Li–Fe–O systems were carried out using differential scanning calorimetry, Knudsen effusion mass spectrometry, and solid-state electrochemical technique based on fluoride electrolyte. Heat capacities of LiFe5O8(s) and LiFeO2(s) were determined in the temperature range 127–861 K using differential scanning calorimetry. Gibbs energies of formation of LiFe5O8(s) and LiFeO2(s) were determined using Knudsen effusion mass spectrometry and solid-state galvanic cell technique. The combined least squares fits can be represented as ΔfGmo(LiFe5O8,s,T)/kJ mol−1 (±6)=−2341+0.6764(T/K) (588≤T/K≤971) ΔfGmo(LiFeO2,s,T)/kJ mol−1 (±3)=−708+0.1656(T/K) (569≤T/K≤1021) The temperature independent term of the above equations represents ΔfHom(Tav) and temperature dependent term represents negative change in entropy of the respective compounds. Thermodynamic analysis shows that LiFe5O8(s) is more stable compared to LiFeO2(s).