Abstract
Abstract The evolution in phase composition resulting from 1400°C ageing of ZrO 2 samples stabilized by ∼4–7 mol.% each of Y 2 O 3 (YSZ), Sc 2 O 3 (ScSZ), or a mixture of Sc 2 O 3 –Y 2 O 3 (SYSZ) was studied by synchrotron radiation X-ray diffraction (SR XRD) using whole powder pattern fitting (WPPF), a recently proposed Rietveld-based method for the simultaneous refinement of phase composition and crystal microstructure. The results suggest that SYSZ has better high temperature tetragonal phase stability than the current state-of-art YSZ. For example, a plasma-sprayed coating of SYSZ (6.57 mol.%Sc 2 O 3 –1.00 mol.%Y 2 O 3 ) remained 96.7% in its original tetragonal phase (presumably t′, c / a of 1.0058) after being aged 100 h at 1400°C and then 24 h at 1480°C, whereas a 4.5 mol.% YSZ coating was transformed into two new tetragonal phases, one a low-stabilizer phase with c / a of 1.0154 (44.8%) and the other a high-stabilizer zirconia phase with c / a of 1.003 (46.5%), with some monoclinic (8.7%) formed. The phase compositions found for the various powder and coating specimens, together with information regarding lattice parameters, crystalline domain size and microstrain, also obtained by WPPF, are discussed in terms of the high-temperature phase stability of the YSZ vs SYSZ systems.
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