Effects of RE3+ Ionic Radius on Monoclinic Phase Content of 8 mol% REO1.5 Partially Stabilized ZrO2 (RE = Yb, Y, Gd, and Nd) Powder Compacts after Annealing at High Temperature

Powders of zirconia doped with 8 mol% REO 1.5 (RE = Yb, Y, Gd, and Nd) were synthesized by using the sol–spray pyrolysis method. The effects of RE 3+ ionic radius on monoclinic (m) phase content of powders were investigated. The XRD results showed that the metastable tetragonal (t′) phase underwent a complete phase change to form m and cubic (c) phases after a heat treatment of 50–100 h at 1450°C. A cation size-dependent reduction in the m phase content of the REO 1.5 partially stabilized ZrO 2 powders was observed. The SEM–EDS analysis of the powders revealed that the RE 3+ concentrations in the c phases decreased with decreasing the RE 3+ ionic radius. These results indicate that the stabilizer concentration of the c phase can be attributed to RE 3+ ionic radii, resulting in different m phase contents. Compared to the REO 1.5 single doped ZrO 2 , the m phase contents of 8 mol% (RE 0.5 Yb 0.5 )–ZrO 2 (RE = Y, Gd, and Nd) powders were significantly reduced. The results prove that the stabilizer with a lower RE 3+ size is effective in reducing the m phase content of partially stabilized ZrO 2 after annealing at high temperatures.