The cubic fluorite-type solid solution of ZrO₂ containing 15 mole % CaO has been prepared by the hot-pressing process. The effects of annealing on the change.of lattice parameter, electrical properties, and density of the solid solution have been investigated. The lattice parameter of the cubic solid solution was found to depend on the heat treatment of the specimens. The decrease of lattice parameter with annealing temperature and time has been interpreted either in terms of the removal of interstitial oxygen ions from the." lattice or in terms of the inhomogeneous distribution of the CaO in the ZrO₂ lattice. The activation energy for conduction was also found to depend on the heat treatment of the specimens. The variation of activation energy with annealing temperature has been interpreted in terms of pairing and clustering of the oxygen vacancies with the substitutional Ca ions in the solid solution. The minimum activation energy obtained in the present investigation corresponded to the theoretically predicted activation energy for the migration of oxygen vacancies. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate