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

The standard molar Gibbs energy of formations of BaFe12O19(s), BaFe2O4(s), Ba2Fe2O5(s), Ba3Fe2O6(s) and Ba5Fe2O8(s) have been determined using solid-state electrochemical technique employing CaF2(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 BaFe12O19(s) has been determined using solid-state electrochemical technique employing CSZ as an electrolyte from 1048 to 1221 K. The values of ΔfGm0(T) for the above ternary oxides are given by (ΔfGm0(BaFe12O19, s)/kJ mol-1(±0.6)=-5431.3+1.5317 (T/K) (970≤T/K≤1151))) (ΔfGm0(BaFe2O4, s)/kJ mol-1(±1.3)=-1461.4+0.3745 (T/K) (970≤T/K≤1151)))(ΔfGm0(Ba2Fe2O5, s)/kJ mol-1(±1.4)=-2038.3+0.4433 (T/K) (970≤T/K≤1149)))(ΔfGm0(Ba3Fe2O6, s)/kJ mol-1(±1.5)=-2700.1+0.6090 (T/K) (969≤T/K≤1150)))and(ΔfGm0(Ba5Fe2O8, s)/kJ mol-1(±1.6)=-3984.1+0.9300 (T/K) (973≤T/K≤1150)))The uncertainty estimates for ΔfGm0 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