System Tb–Fe–O: thermodynamic properties of ternary oxides using solid-state electrochemical cells

Abstract

The standard molar Gibbs free energies of formation of TbFeO 3(s) and Tb 3Fe 5O 12(s) have been determined using solid-state electrochemical cell employing different solid electrolytes. The reversible emfs of the following solid-state electrochemical cells have been measured in the temperature range 1050⩽ T/K⩽1250. Cell ( I):(−) Pt/{ TbFeO 3( s)+ Tb 2 O 3( s)+ Fe( s)}// YDT/ CSZ//{ Fe( s)+ Fe 0.95 O( s)}/ Pt(+) Cell ( II):(−) Pt/{ Fe( s)+ Fe 0.95 O( s)}// CSZ//{ TbFeO 3( s)+ Tb 3 Fe 5 O 12( s)+ Fe 3 O 4( s)}/ Pt(+) The oxygen chemical potentials corresponding to the three-phase equilibria involving the ternary oxides have been computed from the emf data. The standard molar Gibbs free energies of formation of solid TbFeO 3 and Tb 3Fe 5O 12 calculated by the least-squares regression analysis of the data obtained in the present study are given by { Δ f G ∘ m ( TbFeO 3, s)/( kJ· mol −1)±3.2}=−1357.5+0.2531·(T/ K); (1050⩽T/ K⩽1548); and { Δ f G ∘ m ( Tb 3 Fe 5 O 12, s)/( kJ· mol −1)±3.5}=−4901.7+0.9997·(T/ K); (1050⩽T/ K⩽1250). The uncertainty estimates for Δ f G ∘ m include the standard deviation in the emf and uncertainty in the data taken from the literature. Based on the thermodynamic information, oxygen potential diagram and chemical potential diagrams were computed for the system Tb–Fe–O at T=1250 K.