The Al2O3–HfO2–La2O3 phase diagram. II. phase equilibria at 1250 and 1600°C

Abstract

The isothermal sections at 1250 and 1600°C for the Al 2 O 3 -HfO 2 -La 2 O 3 phase diagram are constructed for the first time. No ternary compounds or appreciable regions of solid solutions based on components or binary compounds are found in the ternary system. The triangulation of the system is determined by the La 2 Hf 2 O 7 phase being most thermodynamically stable.

Thermodynamic Modeling of the HfO2–La2O3–Al2O3 System

“…The calculated results are in good agreement with most experimental data. For La 2 O 3 –Al 2 O 3 system, compared with the previous assessments, the thermal stabilities of LaAl 11 O 18 and LaAlO 3 phases are reduced by making their Gibbs energies more positive to get the tie line between Al 2 O 3 and pyrochlore in agreement with ternary experimental data . We fit the experimental heat capacity of LaAlO 3 with expression of C p = 118.764 + 0.0127 T – 2 760 800 T −2 as seen in Fig.…”

“…It should be noted that the two‐phase region of β + P appears with the increase in temperature. However, one sample at the same region at 1873 K observed by Lakiza et al . was three‐phase equilibrium of β + P + LA.…”

“…Lakiza et al . studied the phase equilibria of HfO 2 –La 2 O 3 –Al 2 O 3 system at 1523 and 1873 K by quenching experiment and the quenched samples were analyzed by XRD.…”

“…Calculated isothermal sections of the HfO 2 –La 2 O 3 –Al 2 O 3 system at (a) 1523 K and (b) 1873 K compared with experimental data …”

“…reassessed this system because some new calorimetric data for LaAlO 3 were available. However, it is difficult to reproduce the experimental phase equilibria of HfO 2 –La 2 O 3 –Al 2 O 3 ternary system using the Gibbs energies of LaAl 11 O 18 and LaAlO 3 reported by Fabrichnaya et al . Furthermore, the recent Gibbs energy of formation for LaAlO 3 measured by Jacob et al .…”