Materials Science and Engineering A 386 (2004) 1–9 Microstructural evolution in 8 mol% Y 2 O 3 -stabilized cubic zirconia (8YSCZ) with SiO 2 addition S. Tekeli ∗ , M. Erdogan, B. Aktas Materials Division, Metallurgy Education Department, Technical Education Faculty, Gazi University, 06500 Besevler-Ankara, Turkey Received 22 December 2003; received in revised form 4 June 2004 Abstract The densification, grain-growth and microstructural evolution of high-purity 8 mol% yttria-stabilized cubic zirconia (8YSCZ) with SiO 2 addition were investigated. The addition of 1 wt.% SiO 2 enhanced the sinterability of 8YSCZ, compared with 8YSCZ without additive. In particular, doped 8YSCZ achieved a density of 99% of its theoretical value at 1300 ◦ C, while undoped 8YSCZ reached the same value at 1400 ◦ C. The densification mechanism associated with this process is generally considered attributable to liquid phase sintering. For grain- growth measurements, the specimens sintered at 1400 ◦ C were annealed at 1400, 1500 and 1600 ◦ C for 10, 30 and 66 h. It was seen that grain-growth rate could also be controlled by the deliberate addition of 1 wt.% SiO 2 . A grain-growth exponent of 2 and an activation energy for grain-growth of 298 kJ/mol were obtained for undoped 8YSCZ. The SiO 2 -containing specimens had a grain-growth exponent of 3 and an activation energy of 382kJ/mol. The slow grain-growth in doped 8YSCZ is due to the lower grain boundary mobility and energy, which result from solute segregation in the grain boundary and its drag in doped 8YSCZ but not in undoped 8YSCZ. The drag effect arises from any preferred segregation of impurities either to or from grain boundary area because of size and charge differences. SiO 2 is expected to segregate to grain boundaries. This segregation layer is believed to hinder grain-growth by resulting in limiting matter transfer along the grain boundary. © 2004 Elsevier B.V. All rights reserved. Keywords: Cubic zirconia; Sinterability and grain-growth; SiO 2 1. Introduction Zirconia-based ceramics combine good mechanical prop- erties, such as high strength and toughness with good elec- tronic properties such as high ionic conductivity. Conse- quently they are widely used both as structural and functional materials [1]. Pure zirconia exists in the three different crys- tal structure, i.e., monoclinic, tetragonal and cubic. These phases can be obtained depending on temperature and com- positional ranges under equilibrium conditions [2–4]. Mono- clinic zirconia is present below 1240 ◦ C and is the stable room temperature phase of pure zirconia. Tetragonal zirconia is an intermediate phase, which lies between 1240 and 2370 ◦ C. The retention of the tetragonal phase can be controlled as in the case of cubic zirconia by the formation of a solid so- ∗ Corresponding author. Tel.: +90 312 4399760; fax: +90 312 2120059. E-mail address: stekeli@gazi.edu.tr (S. Tekeli). lution with alloying oxide such as MgO, CaO, Y 2 O 3 and CeO 2 .Y 2 O 3 additions yield an extremely fine grained mi- crostructure known as tetragonal zirconia polycrystal, which has excellent mechanical properties. Cubic zirconia is the highest temperature phase, which is present in the tempera- ture range of 2370 and 2680 ◦ C. However, upon the addition of a few percent of above-stabilizers, the cubic phase can be obtained at lower temperatures [2,3]. The high temperature cubic phase can also be retained at room temperatures as a non-equilibrium phase by rapid cooling such that diffusive transformation does not occur. The cubic form of stabilized zirconia ceramics are of technological importance due to their high oxygen ionic conductivity at around 1000 ◦ C. Their use as solid state electrolytes has allowed the creation of novel application such as oxygen gas sensors, oxygen membrane separators and solid oxide fuel cells (SOFC). High temperature deformation in fine-grained ceramics has been extensively studied in recent years. Large tensile 0921-5093/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2004.07.057