On the nucleation and paracrystal interspacing of Zr-doped Co3−δO4

A paracrystalline array of defect clusters was shown to form in Zr-doped Co3−δO4 spinel in the ZrO2/Co1−xO composites while prepared by a sintering route at 1650 °C in air. Analytical electron microscopic observations indicated the spinel precipitate and its paracrystal predominantly formed at the ZrO2/Co1−xO interface and the cleavages/dislocations of the Co1−xO host. Defect chemistry consideration suggests the paracrystal is due to the assembly of charge- and volume-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 4.9 times the lattice spacing of the average spinel structure of Zr-doped Co3−δO4. This spacing between defect clusters is about 0.98 times that of our previously studied undoped Co3−δO4. There is much larger (3.4 times difference) paracrystalline spacing for Zr-doped Co3−δO4 than its parent phase of Zr-doped Co1−xO.