Review article

Factors Influencing the Stability of Low Temperature Tetragonal ZrO₂

Goran Štefanić ; Division of Materials Chemistry, Ruđer Bošković Institute, P O. Box 180, 10002 Zagreb, Croatia
Svetozar Musić ; Division of Materials Chemistry, Ruđer Bošković Institute, P O. Box 180, 10002 Zagreb, Croatia

Abstract

Various factors that influence the appearance of a tetragonal (t-) ZrO₂ polymorph at room temperature have been extensively investigated. Several proposed models emphasize the role of anionic impurities (SO₄2-, OH-), crystallite size (surface energy), structural similarities between the starting material and t-ZrO₂, lattice strains, water vapor, lattice defects (oxygen vacancies), etc. Our investigations, focused on the stability of low temperature t-ZrO₂, showed that, regardless of the structural differences in the starting zirconium materials, their thermal decomposition products crystallized into a metastable t-ZrO₂. The t-ZrO₂ -> m-ZrO₂ transforma-tion occurred during the cooling or further calcination in the pres-ence of air at atmospheric pressure. On the other hand, if these processes are performed in vacuum, the metastable phase is pre-served. These observations indicate that a metastable t-ZrO₂ appears at room temperature as a result of stabilization caused by introduction of oxygen vacancies, similarly as in the solid Solutions with aliovalent cations. A decrease in the specific surface area of ZrO₂ grains or the presence of the substances that enter into strong surface interactions with ZrO₂ (SO₄2-, Cr₂O₃) prevents the diffusion of oxygen from the atmosphere into the ZrO₂ lattice and due to this fact the metastable t-ZrO₂ is stabilized. On the other hand, lattice strain and grain size of metastable t-ZrO₂ could not be clearly related to its stability.

Keywords

t-ZrO₂; m-ZrO₂; hydrous zirconia; oxygen vacancies; lattice strain; XRD; DSC

Hrčak ID:

129319

URI

https://hrcak.srce.hr/129319

Publication date:

1.8.2002.

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