Phase diagram of nonstoichiometric 10 mol% Gd{sub 2}O{sub 3{minus}}doped cerium oxide determined from specific heat measurements

The phase diagram for nonstoichiometric 10 mol%Gd20{sub 3{minus}}doped cerium oxide, Ce{sub 0.818}Gd{sub 0.182}O{sub 1.909{minus}y}, was determined from specific heat measurements in the temperature range 300-1250 K and composition range Ce{sub 0.818}Gd{sub 0.182}O{sub 1.909}-Ce{sub 0.818}Gd{sub 0.182}O{sub 1.731}, using a controlled diabatic scanning calorimeter. No phase transition was found in this temperature range for the composition Ce{sub 0.818}Gd{sub 0.182}O{sub l.909}. The specific heat measurements reveal phase transitions for the composition range Ce{sub 0.818}Gd{sub 0.182}O{sub l.859}-Ce{sub 0.818}Gd{sub 0.182}0{sub 1.731}. A phase diagram is constructed which shows a miscibility gap. The maximum of the miscibility gap occurs at the composition Ce{sub 0.818}Gd{sub 0.182}O{sub 1.788} and T = 939 K. The phase diagrams of nonstoichiometric CeO{sub 2{minus}x} and Ce{sub 0.818}Gd{sub 0.182}O{sub 1.909{minus}y} are compared and discussed in detail.