Effect of the species of substituted ion on ferroelastic domain switching of rare-earth ion-doped ZrO 2 pseudo-single cr
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Effect of the species of substituted ion on ferroelastic domain switching of rare-earth ion-doped ZrO2 pseudo-single crystals Takanori Kiguchi, Atsushi Saiki, Kazuo Shinozaki, and Nobuyasu Mizutani Department of Inorganic Materials, Faculty of Engineering, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku, Tokyo 152, Japan (Received 26 November 1997; accepted 9 February 1998)
The difference of domain switching amount of 3 mol % R2 O3 –ZrO2 (R Yb, Y, Dy, Gd, Eu, Sm) pseudo-single crystals with additive cation species was investigated from the microstructural aspect. The switching amount of Yb, Y, Dy, and Gd substituted ZrO2 was three times higher than that of Eu and Sm. The amount corresponded to the volume fraction of the t 0 -phase, and it indicated that phase separation proceeded, especially in Eu and Sm substituted ZrO2 . I. INTRODUCTION
Partially stabilized zirconia is a ferroelastic material; therefore ferroelastic domain switching occurs. Oxygen ions, especially, displace by external stress, and consequently a- and c-axes of tetragonal lattice exchange each other. This phenomenon is known to be one of the mechanisms for fracture toughness,1–6 with mainly tetragonal zirconia with a t 0 single phase being studied to date. In the partially stabilized ZrO2 , it has been found that there is mainly 2 types of tetragonal phase. One is the metastable t 0 -phase and the other is the stable t-phase. However, partially stabilized zirconia without quench treatment from the cubic phase is composed not only of thermally metastable t 0 -phase (or c-phase) but also thermally stable t-phase. In our previous study, it was clarified that ferroelastic domain switching of partially stabilized ZrO2 occurred in 2 steps according to the switching of the t 0 -phase domain and that of the t-phase domain, respectively, and that the effect of substituted ionic radius on the ferroelastic domain switching of rare earth ion doped ZrO2 was the increase of the critical stress with the elastic strain energy introduced by substituted ions.7 However, the effect of the substituted ion on the switching amount could not be understood from the viewpoint of the lattice strain. It was found that the switching amount of t 0 -phase domain decreased with the progress of phase separation by annealing 3 mol % R2 O3 –ZrO2 .8 Therefore the purpose of this paper is to study the effect of substituted ions on the switching amount of 3 mol % R2 O3 –ZrO2 (R Yb, Y, Dy, Gd, Eu, Sm) pseudo-single crystals from the microstructural aspect. II. EXPERIMENTAL
The samples used in this work were ZrO2 pseudosingle crystals partially stabilized with 3 mol % rare earth oxides R2 O3 (R Yb, Y, Dy, Gd, Eu, Sm). They were grown by the Xe lamp arc image floating zone method according to the previous study.9,10 The growth 142
J. Mater. Res., Vol. 14, No. 1, Jan 1999
direction was along k100l, which was confirmed by the back reflection Laue method. The composition of the crystals grown was measured with inductively i
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