Oxidation–decomposition facilitated reorientation of nanoparticles in reactively sintered (Ni0.33Co0.67)1−δO polycrystals

(Ni0.33Co0.67)1−δO polycrystals with rock salt structure and a bimodal size distribution due to reactive sintering at 1000 °C were subject to annealing at 720 °C for 2–72 h in air and studied by analytical electron microscopy with regard to the effect of oxidation decomposition on the reorientation of nanoparticles in host grains. Upon annealing, the nanoparticles rapidly oxidized as spinel structure progressively Co-richer, whereas the host protoxide grains with rock salt-type structure progressively Ni-richer. The spinel particles less than 100 nm in size readily detached from grain boundaries and fell into parallel epitaxial relationship with respect to the host protoxide grains sharing a coherent interface. Such a Brownian-type reorientation process, in terms of anchorage release at interphase interface and driven by epitaxy energy cusp, at a rather low apparent homologous temperature (T/Tm=0.45) was facilitated by oxidation decomposition process and nanometer-size effect.