Effect of Dopant Species on Tetragonal (t′)‐to‐Monoclinic Phase Transformation of Arc‐Melted ZrO₂‐RO,_1.5 (R = Sm, Y, Er, and Sc) in Water at 200°C and 100 MPa Pressure

Arc‐melted specimens of rare‐earth‐doped zirconia (ZrO₂‐X mol% RO_1.5; X= 4–10 for R = Sm, Y, Er, and X= 4–18 for Sc) were hydrothermally treated at 200°C, 100 MPa to investigate the dependence of the tetragonal‐to‐monoclinic transformation on dopant species and its content. The volume fraction of monoclinic phase Vm(t) increased from Vm(0) to a certain saturated value Vm(ω), following [Vm(t) −Vm(0)]/[Vm(t) −Vm(ω)] = 1 − exp(−k·t), where t is the annealing time at 200°C, 100 MPa. The transform‐abilities, Vm(0), Vm(ω), and k decrease with increasing dopant content. The Vm(ω) decreased with an increase of ionic radius of dopants. The relation 0 < Vm(ω) < 1 suggests that apparent noncompositional inhomogeneity exists in the hydrothermally treated sample.