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.

Physicochemical methods are used to study the phase equilibria during crystallization of alloys in the Al 2 O 3 -HfO 2 -La 2 O 3 system for the first time. Liquidus and solidus projections onto the concentration triangle, a melting diagram, and a crystallization scheme are constructed. No new ternary compounds and appreciable ranges of ternary solid solutions are found in the system.

The phase equilibria during crystallization of alloys in the Al 2 O 3 -HfO 2 -Gd 2 O 3 system are studied for the first time by physicochemical methods. The liquidus and solidus surfaces on the composition triangle as well as the melting diagram and crystallization scheme are constructed. No new ternary compounds or appreciable ternary solid solution regions are found in the system. The maximum temperature in the system is 2820°C and corresponds to the AL + F + GA (E 3 ) three-phase eutectic.Since crystallization in the system finishes with eutectic reactions, it allows materials of the quasiternary system to combine the unique properties of HfO 2 -based T and F solid solutions and the properties of other phases in composite materials.