On the surface morphology of solution annealed Co_(1-x)O-MgO-Effects of directional dislocation exposure and Co_(1-x)O condensation

摘要

The sintered Co_(1-x)O ceramics with or without 20 mol percent MgO solid solution in the rock salt type structure were annealed in the temperature range of 400-1500 deg C in air for surface morphology development study. Electron microscopic observations indicated the MgO component considerably suppressed the thermal etching and the nucleation of the Co-rich spinel as expected. Surprisingly, prolonged annealing at 1500 deg C caused anisotropic development of the {111}/{100}-faceted etch pits/hillocks from the cubic crystal system, which can be rationalized by the predominant exposure of <110> oriented dislocations on the {111} surfaces. Meanwhile, sublimation-condensation at this temperature caused cube-like Co_(1-x)O crystallites to deposit preferentially on the (100) surface following parallel or 45 deg off crystallographic relationship via Brownian motion of the crystallites.