Mechanisms of room temperature metastable tetragonal phase stabilisation in zirconia

Abstract

Mechanisms of tetragonal phase stabilisation, at room temperature, in nanocrystalline (,100 nm), submicrometre-sized (100 nm-1 mm), and bulk zirconia (ZrO 2 ) (.1 mm) are reviewed in detail. The merits, demerits and scope of each individual model are outlined. The analysis of the literature shows that, although the mechanism of tetragonal phase stabilisation in bulk ZrO 2 is well understood, the room temperature tetragonal phase stabilisation mechanism in undoped, nanocrystalline ZrO 2 is controversial. Various proposed models, based on surface energy (nanocrystallite size), strain energy, internal and external hydrostatic pressure, structural similarities, foreign surface oxides, anionic impurities, water vapour and lattice defects (oxygen ion vacancies), are discussed in detail. It is proposed that generation of excess oxygen ion vacancies within the nanocrystalline ZrO 2 is primarily responsible for the room temperature tetragonal phase stabilisation, below a critical size. Hence, the mechanism of tetragonal phase stabilisation in nanocrystalline ZrO 2 appears to be the same as that in doped ZrO 2 (at room temperature) and undoped ZrO 2 (at higher temperature).

Peridynamic simulations of the tetragonal to monoclinic phase transformation in zirconium dioxide

“…Exposure of manufactured zirconia to moist environments up to ~400°C has been shown to cause the tetragonal phase to transform to monoclinic, this phenomenon is referred to as low temperature, or hydrothermal, degradation (Chevalier et al, 2009;Eichler et al, 2007;Guo and Schober, 2004;Shukla and Seal, 2005). These conditions are very similar to those experienced by oxidising zirconium alloys in nuclear reactors or autoclaves, and these oxide films also demonstrate a continuous reduction in tetragonal phase fraction and degradation in the protective character of the oxide layer (Petigny, 2000;P.…”

“…These values are much greater than those of ΔU STRAIN and ΔU SURFACE discussed in this manuscript, and as such it appears that the transformation should occur regardless of the applied load or fracture behaviour. ΔG C could be reduced significantly by the introduction of oxygen vacancies (Shukla and Seal, 2005), either by doping elements (Li and Chen, 1994), or as a product of the oxidation of zirconium alloys (Ni et al, 2012). However, these results indicate that factors modifying the chemical free energy change could have the greatest impact on whether the phase transforms or not.…”

“…The reduction of tin in zirconium-niobium alloys has been shown to produce oxide layers with a lower tetragonal phase fraction Wei et al, 2013). A proposed theory behind this mechanism is that introducing a doping element with a lower valence state than Zr 4+ may stabilise the presence of oxygen vacancies, which in turn distort the lattice and make the tetragonal phase more energetically favourable (Fabris et al, 2002;Guo and Schober, 2004;Ho and Tuan, 2011;Shukla and Seal, 2005). As zirconium alloys oxidise entirely due to the inward migration of oxygen ions (Cox, 2005), there should be an increasing concentration of oxygen vacancies approaching the metal-oxide interface from the oxide surface (Cox and Pemsler, 1968;Na Ni et al, 2011;Yoo, 2001).…”

Synthesis optimization of carbon-supported ZrO2 nanoparticles from different organometallic precursors

“…ZrO 2 exists in three phases, viz., monoclinic (a room temperature stable phase), tetragonal (stable above 1100°C), and cubic (stable above 2300°C); the latter two are thus called hightemperature phases [1]. Various mechanisms are reported which explain the stabilization of high-temperature ZrO 2 phases at room temperature [2,3]. ZrO 2 stabilized with dopants like yttria, magnesia, and alumina has a wide range of applications in solid-oxide fuel cells, thermal barrier coatings, and biomedical implants [4][5][6].…”

Zirconia nanoparticles: a martensitic phase transition at low temperature

“…Pure zirconia exhibits three well-defined crystallographic forms, namely the monoclinic, tetragonal, and cubic polymorphs. The tetragonal phase, normally stable at high temperature for the case of coarse grain ceramics, has been observed stable or metastable at room temperature [6]. Since Ruff and Ebert's [1] pioneering report in 1929 on the existence of a reversible tetragonal to monoclinic martensitic transformation in pure zirconia, much effort has been dedicated to understanding the details of this transformation.…”