(111)-Specific reorientation and shape change of Co1−xO particles within CaO grains

The Co1−xO/CaO powders 1:9 in molar ratio were sintered and annealed at a rather high homologous temperature of 0.97 (1300 °C) for 5 and 80 h in air. Transmission electron microscopy indicated that the intragranular Co1−xO particles less than 0.7 μm in size, but not larger, fell into two epitaxial crystallographic relationships with respect to host CaO grains: predominantly [11̄1]Co1−xO//[11̄1]CaO, [011]Co1−xO//[1̄12]CaO with a well developed (11̄1) habit plane and less commonly [111̄]Co1−xO//[111̄]CaO, [011]Co1−xO//[011]CaO with multiple yet less matched {111} habit planes. The primary epitaxial particles further changed into lath-like by forming a coherent (11̄1)Co1−xO/(11̄1)CaO interface at the expense of incoherent (111)Co1−xO/(hkl)CaO edges. Size and interfacial energetics dependence of orientation change of intragranular particles is in accordance with the mechanism of Brownian-type rotation of particles in terms of anchorage release at the Co1−xO/CaO interface.