Size effect of trivalent oxides on low temperature phase stability of 2Y-TZP

2 mol% Y₂O₃stabilized-TZPs (2Y-TZPs) doped with oversized trivalent cations (Sc³⁺< Yb³⁺< Y³⁺< Sm³⁺< Nd³⁺< La³⁺) whose ionic radius is larger than Zr⁴⁺was sintered for 1 h at 1500°C over the range containing trivalent oxides from 0 to 2 mol% with 0.5 mol% interval to evaluate the effect of trivalent cation alloying on low temperature phase stability of 2Y-TZP by investigating the variation of Raman spectra and lattice parameters. For a given concentration of dopant, tetragonality (c/aaxial ratio) increases with raising the dopant size. However, monoclinic (m)-ZrO₂content for the specimens annealed for 500 h at 220°C in air firstly decreases with increasing dopant size and then increases as dopant size is greater than Y³⁺ion. Raman modes of Zr-O_II(260 cm^–1) and Zr-O_I(640 cm^–1) shift to higher wavenumbers only when Sm₂O₃, Nd₂O₃, and La₂O₃are added. Although full width at half maximum (FWHM) of 640 cm^–1is constant, FWHM of 260 cm^–1mode decreases with increasing dopant size, indicating that an ordered structure (pyrochlore phase) may be formed. Therefore, dopant size is dependent on phase stability of 2Y-TZP in this system.