Thermodynamic Assessment of the La-Fe-O System

Abstract

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 La 1±x Fe 1±y O 32d 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 LaFeO 3 due to a magnetic orderdisorder transition is included in the model description. Lanthanum-doped hexaferrite, LaFe 12 O 19 , is modeled as a stoichiometric phase. D f,elements°H298 K (LaFe 12 O 19 ) = 25745 kJ/mol,°S 298 K (LaFe 12 O 19 ) = 683 J/mol AE K, and D f,oxides°G (LaFe 12 O 19 ) = 4634 2 37.071T (J/mol) from 1073 to 1723 K are calculated. The liquid phase is modeled using the two-sublattice model for ionic liquids. The calculated La-Fe phase diagram, LaO 1.5 -FeO x phase diagrams at different oxygen partial pressures, and phase equilibria of the La-Fe-O system at 873, 1073, and 1273 K as a function of oxygen partial pressures are presented.

Thermodynamic stability of stoichiometric LaFeO3 and BiFeO3: a hybrid DFT study

“…Exploration of formation energies of LFO was performed in many experimental studies [9][10][11][12][13][14] using various calorimetric and electrochemical techniques. However, spread of Gibbs free energy of formation of LFO from La2O3 and Fe2O3 oxides obtained in different experiments is very large: from 13 23 kJ/mol to 92 kJ/mol .…”

Defect Chemistry and Phase Equilibria of (La1-xCax)FeO3-δThermodynamic Modeling

“…There are many possible interactions Figure 1 depicts the compositional space for LCFO showing only major defects in the system with cation vacancies omitted, and the shaded triangle represents the electrically neutral combinations of species. Since LaFeO 3-δ perovskite was already modeled, 14 the interaction parameters in the top plane are fixed. Since LaFeO 3-δ perovskite was already modeled, 14 the interaction parameters in the top plane are fixed.…”

“…Eq. The Gibbs energy function for GVVV is common for most perovskite modeling 6,8,14 and taken from Grundy's work 8 for compatibility of perovskite databases. Among the 16 end-members, 8 of them have vacancy in the first sublattice and are the same as in the LaFeO 3-δ system.…”

“…3 in the present paper. [6][7][8][9]14 and assuming ideal mixing, the above Gibbs energies of neutral compounds can be related to the Gibbs energies of corresponding end-members as follows, Their Gibbs energy functions are thus taken from the LaFeO 3-δ modeling.…”

“…However, the detailed defect mechanism and its thermodynamics property through which the Ca doping on A-site affects the valence state of B-site iron and the oxygen vacancies are not fully understood. [12][13][14][15][16][17] The paper is organized as follows. 2 The present work thus aims to develop a comprehensive understanding of defect chemistry and phase equilibria of LCFO through thermodynamic modeling of the phase using the CALPHAD (CALculation of PHAse Diagram) approach.…”