Cellular Paracrystal Formation from Co-Doped CaO Polycrystals

A paracrystalline array of defect clusters was shown to form in Co-doped CaO polycrystals while prepared by a sintering route at 1300°C in air. Analytical electron microscopic observations indicated the paracrystal predominantly formed at dislocations and in the area left behind the migrating grain boundaries, exhibiting cellular structure. Defect chemistry consideration suggests the paracrystal is due to the assembly of volume- and charge-compensating defects of the 4:1 type with four octahedral vacant sites surrounding one Co3+-filled tetrahedral interstitial site. The interspacing of such defect clusters is approximately 4.3 times the lattice spacing of the average rock salt structure of Co-doped CaO. This spacing between defect clusters is about 2.7 times that of our previously studied Ni-doped CaO.