Experimental Phase Diagram Determination and Thermodynamic Assessment of the CeO 2 ‐ Gd 2 O 3 ‐ CoO System

New phase diagram data and a thermodynamic assessment of the CeO ‐ Gd 2 O 3 ‐ CoO system using the CALPHAD approach are presented. This information is needed to understand the surprisingly low sintering temperature (950°C–1050°C) of CeO 2 ‐based materials doped with small amounts of transition metal oxide (e.g., CoO ). Experimental phase equilibria between 1100°C and 1300°C are reported based on the analysis of annealed and molten samples. No isolated compound exists in the ternary. At 1300°C the Co solubility in the ternary compounds Ce 1− x − y Gd x Co y O 2− x /2− y (fluorite) is 2.7 mol% and is less than 1 mol% in the Gd 2− x Ce x O 3+ x /2 (bixbyite). The Ce solubility in the perovskite GdCoO 3−δ was found to be 1 mol%. The lowest temperature eutectic melt in the ternary has a composition of 57.2 mol% Co and 41.1 mol% Gd melting at an onset temperature of 1303 ± 5°C, which is close to the binary eutectic in the Gd 2 O 3 ‐ CoO system at 60 ± 2 mol% Co and 1348 ± 1°C.