Thermodynamic properties of ternary oxides in the system Ba–Fe–O using solid-state electrochemical cells with oxide and fluoride ion conducting electrolytes

Abstract

The standard molar Gibbs energy of formations of BaFe 12O 19(s), BaFe 2O 4(s), Ba 2Fe 2O 5(s), Ba 3Fe 2O 6(s) and Ba 5Fe 2O 8(s) have been determined using solid-state electrochemical technique employing CaF 2(s) as an electrolyte. The reversible e.m.f. values have been measured in the temperature range from 970 to 1151 K. The oxygen chemical potential corresponding to three phase equilibria involving technologically important compound BaFe 12O 19(s) has been determined using solid-state electrochemical technique employing CSZ as an electrolyte from 1048 to 1221 K. The values of Δ f G m 0( T) for the above ternary oxides are given by Δ f G m 0( BaFe 12 O 19, s)/ kJ mol −1(±0.6)=−5431.3+1.5317 (T/ K) (970⩽T/ K⩽1151) Δ f G m 0( BaFe 2 O 4, s)/ kJ mol −1(±1.3)=−1461.4+0.3745 (T/ K) (970⩽T/ K⩽1151) Δ f G m 0( Ba 2 Fe 2 O 5, s)/ kJ mol −1(±1.4)=−2038.3+0.4433 (T/ K) (970⩽T/ K⩽1149) Δ f G m 0( Ba 3 Fe 2 O 6, s)/ kJ mol −1(±1.5)=−2700.1+0.6090 (T/ K) (969⩽T/ K⩽1150) and Δ f G m 0( Ba 5 Fe 2 O 8, s)/ kJ mol −1(±1.6)=−3984.1+0.9300 (T/ K) (973⩽T/ K⩽1150) The uncertainty estimates for Δ f G m 0 includes the standard deviation in the e.m.f. and uncertainty in the data taken from the literature. An isothermal oxygen potential diagram for the system Ba–Fe–O was constructed at 1100 K based on the thermodynamic data obtained in this study.