In high-purity yttria-stabilized tetragonal zirconia with a grain size of 0.35 μm, deformation at grip portions and concurrent grain growth strongly affect the tensile creep at 1673 K and lead to the spurious determination of the stress exponent at low stresses. Analysis of strain rates directly along the gauge portion of each creep specimen reveals a sigmoidal stress-strain rate relationship such that there is a high stress region with n = 2.7, a low stress region with n = 1.6, and a transient region connecting the former regions appear in a stress range of 3 to 80 MPa. A decreasing n-value toward unity incorporated with a grain size exponent of 2.0 at low stresses suggests an intervention of diffusional creep in the low stress region.
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