Structure and Ionic Mobility of Zirconia at High Temperature

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Abstract
The high‐temperature structure of zirconia was studied by powder neutron diffraction up to 2400°C. The boundaries of the domain of the nonstoichiometric tetragonal form are defined. They are consistent with a tetragonal‐cubic transition at 2350°C for stoichiometric zirconia. The changes in the structural parameters of the tetragonal form (unit‐cell, positional parameters and thermal B factors) with temperature give evidence of medium zirconium and oxygen mobilities. The oxygen ions are, however, always more mobile than the zirconium ions. An enhancement with temperature of the structural an‐isotropy tends to weaken the weaker of the two distinct Zr‐0 bonds of the tetragonal zirconia. It results in the transformation into the cubic form which is accompanied by a change in unit‐cell volume; this change becomes sharper as the composition tends toward stoichiometry. This transition is probably followed by an increase of the ionic mobility.

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