Transformation-enabled cleaving and healing in zirconia dispersed Co1−xO

Zirconia-polymorphism-induced cleaving and spontaneous healing by precipitation was studied in Co1−xO polycrystals containing a dispersion of ZrO2 particles. Conventional, analytical, and high-resolution transmission electron microscopy indicated that upon cooling the Co1−xO matrix cleaves parallel to {1 0 0} and {1 1 0} planes and heals by itself by co-precipitation of parallel–topotaxial ZrO2/Co3−δO4 particles upon cooling. Due to size effect and matrix constraint, nanometer-size ZrO2 precipitates at cleavages were able to retain tetragonality upon further cooling to room temperature.