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 Δ f H m ° ( 298.15 K ) and standard molar heat capacity (Cp°) were obtained from the solution calorimetry and calvet calorimetric measurements. Δ f H m ° ( 298.15 K ) 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 C p ° with temperature can be given as C p ° ( Bi 2 Fe 4 O 9 ,s ) ( J K - 1 mol - 1 ) = 353.81 + 0.01774 T - 1.63606 × 10 5 / T 2 ( 313 < T / K < 911 ) C p ° ( BiFeO 3 ,s ) ( J K - 1 mol - 1 ) = 116.72 + 0.00968 T - 1.9273 × 10 5 / T 2 ( 313 < T / K < 911 ) and C p ° ( Bi 25 FeO 39 ,s ) ( J K - 1 mol - 1 ) = 1339.21 + 0.16550 T - 28.3546 × 10 5 / T 2 ( 324 < T / K < 834 ) . The standard Gibbs energy of formation of the above compounds have been derived using the values of Δ f H m ° ( 298.15 K ) , C p ° and the estimated Δ f S m ° ( 298.15 K ) .