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

Abstract

2 mol% Y2O3 stabilized-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 degreesC 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/a axial ratio) increases with raising the dopant size. However, monoclinic (m)-ZrO2 content for the specimens annealed for 500 h at 220 degreesC 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 La2O3 are added. Although full width at half maximum (FWHM) of 640 cm(-1) is constant, FWHM of 260 cm(-)1 mode 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. (C) 2001 Kluwer Academic Publishers.