2.19.4 Point Defects and Crystal Density in ZrO₂ when doped with CaO

CaO doping in ZrO₂ allows stabilization of high temperature tetragonal or cubic polymorphs of ZrO₂  at room temperature as a metastable phase.

CaO doping also introduces the defects according to

(1)

OR

(2)

From (1), oxygen vacancies formed allow ZrO₂ to possess high ionic conductivity as a result cubic ZrO₂ is used as electrolyte. When CaO in ZrO₂ dissolves substitutionally, it has to be compensated by creation of a positive charge.

These substitutions also lead to a change in crystal density of ZrO₂.

Figure 2.10 Density of ZrO2 as a function of CaO doping

For more case studies, readers are referred to  Chapter 2 of Physical Ceramics by Chiang, Birnie and Kingery (see bibliography).