Abstract:The thermodynamic properties of Fe₂Ti₃0₉ and Fe₂TiO₅ were measured by means of the following solid state electrolyte cells:
    Pt，Fe+“Fe0”‖ZrO₂ (CaO)‖FeTiO₃+Fe₂Ti₃O₉+Fe₂O₃，Pt
    Pt,  Fe+“Fe0”‖ZrO₂(CaO)‖FeTiO₃+Fe₂TiO₅+TiO₂，Pt
    From the experimental data，the Gibbs energies of formation of Fe₂Ti₃O₉ and Fe₂TiO₅  were obtained:
△G⁰_pr (kJ .mol^-1)= -3459.7-0.847T，(1053 K＜T＜l153K)
△G⁰_pb (kJ .mol^-1) =-1700.2-0.465T，(1173K＜T＜1273K)
 Experimental results fit approximately to those of estimation.

Key words: Fe­₂Ti₃O₉  Fe₂TiO₅  thermodynamic  property  solid state  electrolyte cell