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 5O 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 5O 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 5O 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 5O 8(s) is more stable compared to LiFeO 2(s).