The La-Fe and the La-Fe-O systems are assessed using the Calphad approach, and the Gibbs energy functions of ternary oxides are presented. Oxygen and mutual La and Fe solubilities in body-centered cubic (bcc) and face-centered cubic (fcc) structured metallic phases are considered in the modeling. Oxygen nonstoichiometry of perovskite-structured La1±x Fe1±y O3−δ is modeled using the compound energy formalism (CEF), and the model is submitted to a defect chemistry analysis. The contribution to the Gibbs energy of LaFeO3 due to a magnetic order-disorder transition is included in the model description. Lanthanum-doped hexaferrite, LaFe12O19, is modeled as a stoichiometric phase. Δf,elements°H 298K (LaFe12O19)=−5745kJ/mol, °S 298K (LaFe12O19)=683J/mol·K, and Δf,oxides°G (LaFe12O19)=4634−37.071T (J/mol) from 1073 to 1723K are calculated. The liquid phase is modeled using the two-sublattice model for ionic liquids. The calculated La-Fe phase diagram, LaO1.5-FeO x phase diagrams at different oxygen partial pressures, and phase equilibria of the La-Fe-O system at 873, 1073, and 1273K as a function of oxygen partial pressures are presente

Chen, M.

Gauckler, L.

Grundy, A.

Ivas, T.

Povoden-Karadeniz, E.

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Thermodynamic Assessment of the La-Fe-O System

The La-Cr and the La-Cr-O systems are assessed using the Calphad approach. The calculated La-Cr phase diagram as well as LaO1.5-CrO1.5 phase diagrams in pure oxygen, air, and under reducing conditions are presented. Phase equilibria of the La-Cr-O system are calculated at 1273K as a function of oxygen partial pressure. In the La-Cr system reported solubility of lanthanum in bcc chromium is considered in the modeling. In the La-Cr-O system the Gibbs energy functions of La2CrO6, La2(CrO4)3, and perovskite-structured LaCrO3 are presented, and oxygen solubilities in bcc and fcc metals are modeled. Emphasis is placed on a detailed description of the perovskite phase: the orthorhombic to rhombohedral transformation and the contribution to the Gibbs energy due to a magnetic order-disorder transition are considered in the model. The following standard data of stoichiometric perovskite are calculated: $$ \Updelta_{\text{f,oxides}} {^{\circ }H}_{{298{\rm K}}} ( {\text{LaCrO}}_{ 3} )= - 7 3. 7 {\text{ kJ}}\,{\text{mol}}^{-1} $$ , and $$ {}^{\circ } S_{{298\,{\text{K}}}} ( {\text{LaCrO}}_{ 3} )= 109.2{\text{ J}}\,{\text{mol}}^{ -1}\, {\text{K}}^{ -1} $$ . The Gibbs energy of formation from the oxides, $$ \Updelta_{\text{f,oxides}} {^{\circ } G} ( {\text{LaCrO}}_{ 3} )= -72.403 - 0.0034$$ T (kJmol−1) (1273-2673K) is calculated. The decomposition of the perovskite phase by the reaction $$ {\text{LaCrO}}_{3} \to \frac{1}{2}{\text{La}}_{2} {\text{O}}_{3} + {\text{Cr}} + \frac{3}{4}{\text{O}}_{2} ({\text{g}}) \uparrow $$ is calculated as a function of temperature and oxygen partial pressure: at 1273K the oxygen partial pressure of the decomposition, $$ p_{{{\text{O}}_{{\text{2}}} {\text{(decomp)}}}} = 10^{-20.97}\,{\text{Pa}}$$ . Cation nonstoichiometry of La1-x CrO3 perovskite is described using the compound energy formalism (CEF), and the model is submitted to a defect chemistry analysis. The liquid phase is modeled using the two-sublattice model for ionic liquid

Thermodynamic Assessment of the La-Fe-O System

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