Phase Relations In The Pseudo‐Ternary System La₂O₃–SrO–Fe₂O₃

Abstract

The phase relations in the pseudo‐ternary system La2O3–SrO–Fe2O3 have been investigated in air. Isothermal sections at 1100° and 1300°C are presented based on X‐ray diffraction and thermal analysis of annealed samples. Extended solid solubility was observed for the compounds Srn+1−vLavFenO3n+1−δ (n=1, 2, 3, and ∞) and Sr1−xLaxFe12O19, while only limited solubility of La in Sr4−zLazFe6O13±δ was observed. At high Fe2O3 content, a liquid with low La2O3 content was stable at 1300°C.

Sintering behaviour of La1−xSrxFeO3−δ mixed conductors

“…14,15 The four non-stoichiometric materials (La09, La085, La80 and La65) contained secondary phases in accord with the nominal stoichiometry and phase diagrams of the system SrO-La 2 O 3 -Fe 2 O 3 reported by Fossdal et al. 16 In La085 the secondary phase changed from Fe 2 O 3 in the calcined powder to La 1−x Sr x Fe 12 O 19 in the sintered specimens, which is also in accord with the phase diagrams. 16 Generally, the diffraction lines of the secondary phases were easier to observe in sintered samples compared to the powders due to particle size broadening and reactions with moisture, which was particularly a problem with the powders containing La 2 O 3 as secondary phase.…”

“…16 In La085 the secondary phase changed from Fe 2 O 3 in the calcined powder to La 1−x Sr x Fe 12 O 19 in the sintered specimens, which is also in accord with the phase diagrams. 16 Generally, the diffraction lines of the secondary phases were easier to observe in sintered samples compared to the powders due to particle size broadening and reactions with moisture, which was particularly a problem with the powders containing La 2 O 3 as secondary phase. The average particle size of the powders calculated from the surface area assuming spherical morphology, given in Table 1, was confirmed by electron microscopy.…”

“…The formation of the liquid phase at Fe-excess relative to La 1−x Sr x FeO 3−δ as for La085 and La065 is also previously reported. 16 The rapid swelling observed at 1380 and 1320 • C for La085 and La065 can be interpreted as the solidus temperature in the pseudo binary systems La 1−x Sr x Fe 12 O 19 -La 1−y Sr y FeO 3−δ . An increasing solidus temperature with increasing Sr-content is in line with the Gibbs phase rule and is also in line with previous observations of solidus temperatures.…”

“…An increasing solidus temperature with increasing Sr-content is in line with the Gibbs phase rule and is also in line with previous observations of solidus temperatures. 16 Mizusaki et al 1 have shown that LSF materials become oxygen deficient at elevated temperatures due to the heterogeneous Fig. 9.…”

“…16 The extensive swelling of La085 and La065 were caused by the formation of a liquid phase due to presence of the secondary phases Fe 2 O 3 and La 1−x Sr x Fe 12 O 19 . The formation of the liquid phase at Fe-excess relative to La 1−x Sr x FeO 3−δ as for La085 and La065 is also previously reported.…”