Thermodynamic studies on lithium ferrites

Abstract 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 LiFe 5 O 8 (s) and LiFeO 2 (s) were determined in the temperature range 127–861 K using differential scanning calorimetry. Gibbs energies of formation of LiFe 5 O 8 (s) and LiFeO 2 (s) were determined using Knudsen effusion mass spectrometry and solid-state galvanic cell technique. The combined least squares fits can be represented as Δ f G m o (LiFe 5 O 8 ,s, T )/kJ mol −1 (±6)=−2341+0.6764( T /K) (588≤ T /K≤971) Δ f G m o (LiFeO 2 ,s, T )/kJ mol −1 (±3)=−708+0.1656( T /K) (569≤ T /K≤1021) The temperature independent term of the above equations represents Δ f H o m ( T av ) and temperature dependent term represents negative change in entropy of the respective compounds. Thermodynamic analysis shows that LiFe 5 O 8 (s) is more stable compared to LiFeO 2 (s).