Electron microscopy
 
Additive-stabilized ZrO2
- Practical Electron Microscopy and Database -
- An Online Book -
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This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
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The cubic phase of ZrO2 is not thermodynamically stable. In practical applications, to stabilize the crystal structures, a small amount of stabilizers  (divalent or trivalent oxides of cubic symmetry) such as MgO, CaO, Y2O3, CeO2, Sc2O3 or Yb2O3 need to be added to stabilize the ZrO2 to the cubic phase. The additive oxide cation enters the crystal lattice and then increases the ionic character of the metal-oxygen bonds.  Note that the cubic phase is still not stable below ~1400 °C for MgO additions, ~1140 °C for CaO additions, and ~750 °C for Y2O3 additions. However, the diffusion rates for the cations are very low at these subsolidus temperatures so that the cubic phase can easily be quenched and retained as a metastable phase.

Stabilized zirconia, with its simple open cubic structure, has many applications. However, it is especially susceptible to oxygen diffusion through oxygen vacancies. The addition of 9 mol% Y2O3 produces ~4.1% vacancies and leads to an ionic conductivity of 300-500 ohm-cm at 1000 °C. This ionic conductivity is used in oxygen sensing, solid oxide fuel cells (SOFCs), and heating element applications.

 

 

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