FORMATION OF FLUORITE-RELATED PHASES BY RAPID QUENCHING OF Gd//3TaO//7.

A disorder phase with a cubic pyrochlore lattice (space group Fd3m) was obtained by rapid quenching of a Gd//3TaO//7 (3 Gd//2O//3 multiplied by (times) Ta//2O//5) melt. A fluorite-related phase with orthorhombic weberite lattice (C 222//1) was formed both by firing at 1350 degree C for 96 h or at 1700 degree C for 4 h, and by melting of the 3 Gd//2O//3 plus Ta//2O//5 mixture. Annealing at 1350 degree C for 96 h or at 1700 degree C for 4 h of the rapidly quenched pyrochlore also produced the weberite phase. Order-disorder transition may occur above 1700 degree C in this compound.