Standard enthalpy of formation and heat capacity of compounds in the pseudo-binary Bi2O3-Fe2O3 system

Bismuth ferrites, Bi2Fe4O9, BiFeO3, and Bi25FeO39 have been prepared and characterized. The thermodynamic data such as standard molar enthalpies of formation ΔfHmo(298.15K) and standard molar heat capacity (Cpo) were obtained from the solution calorimetry and calvet calorimetric measurements. ΔfHmo(298.15K) for Bi2Fe4O9(s), BiFeO3(s), and Bi25FeO39(s) were found to be (-2476.0 ± 4.3), (-768.4 ± 2.9) and (-7699.8 ± 17.3) kJ mol-1, respectively. The dependence of molar heat capacity Cpo with temperature can be given as Cpo(Bi2Fe4O9,s)(JK-1mol-1)=353.81+0.01774T-1.63606x105/T2(313<T/K<9 11), Cpo(BiFeO3,s)(JK-1mol-1)=116.72+0.00968T-1.9273x105/T2(313<T/K<911) and Cpo(Bi25FeO39,s)(JK-1mol-1)=1339.21+0.16550T-28.3546x105/T2(324<T/ K<834. The standard Gibbs energy of formation of the above compounds have been derived using the values of ΔfHmo(298.15K), Cpo and the estimated ΔfSmo(298.15K)