The ZrO2-GdO1.5 system is of interest, since materials based on co-doping of zirconia with Y and Gd are attractive as possible new thermal barrier coatings. However, phase equilibria data concerning this system are very limited and not consistent. The establishment of a precise phase diagram in whole composition and temperature ranges is thus of high importance. In the present work, totally 27 samples have been prepared by two kinds of chemical method and sintered in air at 1400 °C for 20 h and additionally for 240 h after intermediate grinding. Samples on GdO1.5-rich side were also annealed at 1600°C for 48 h. The XRD, SEM/EDX, TEM, DTA are employed to obtain the structure information, phase boundary data and phase evolution behavior. With the help of high-temperature calorimeter, heat capacity of pyrochlore phase at five compositions was measured between 100°C and 1400°C.
Based on the experimental phase equilibria and thermodynamic data from literature and those obtained in the present work, the ZrO2-GdO1.5 system has been thermodynamically assessed. The ordered pyrochlore phase is described with a five sublattice ionic solution model (Gd+3,Zr+4)2(Zr+4,Gd+3)2(O-2,Va)6(O-2)1(Va,O-2)1. Most of the experimental data are reproduced within the experimental errors.