Crystallite and Grain-Size-Dependent Phase Transformations in Yttria-Doped Zirconia

• Published in: Journal of the American Ceramic Society 2003-02, Vol.86 (2), p.360-362
• Main Authors: Suresh, Arun, Mayo, Merrilea J., Porter, Wallace D., Rawn, Claudia J.
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Crystalline state (including molecular motions in solids); Crystallographic aspects of phase transformations; pressure effects; Exact sciences and technology; grain size; phase transformation; Physics; Structure of solids and liquids; crystallography; zirconia: yttria-stablized
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/j.1151-2916.2003.tb00025.x

In pure zirconia, ultrafine powders are often observed to take on the high‐temperature tetragonal phase instead of the “equilibrium” monoclinic phase. The present experiments and analysis show that this observation is one manifestation of a much more general phenomenon in which phase transformation temperatures shift with crystallite/grain size. In the present study, the effect of crystallite (for powders) and grain (for solids) size on the tetragonal → monoclinic phase transformation is examined more broadly across the yttria–zirconia system. Using dilatometry and high‐temperature differential scanning calorimetry on zirconia samples with varying crystallite/grain sizes and yttria content, we are able to show that the tetragonal → monoclinic phase transformation temperature varies linearly with inverse crystallite/grain size. This experimental behavior is consistent with thermodynamic predictions that incorporate a surface energy difference term in the calculation of free‐energy equilibrium between two phases.