Diffusion couples of metal alloys were commonly used to study Kirkendall pore formation and amorphization near the interface of composition discontinuity. In this work, yttria-partially stabilized zirconia (Y-PSZ) powders mixed with Co(1-x)O (1:99 molar ratio, denoted as Z1C99) were sintered and annealed at 1600 degrees C for 1-75 h to study interdiffusion-induced defect microstructures of Co(1-x)O near confined Y-PSZ particles. Analytical electron microscopic analysis indicated a much larger flux of Co(2+) from Co(1-x)O into Y-PSZ compared to the reverse flux of Zr(4+) and Y(3+). In addition, there is a significant inward flux of oxygen from Y-PSZ into Co(1-x)O. A net vacancy flux in the opposite direction of ion flux then caused the formation of Kirkendall pores and dislocations in Co(1-x)O near corrugated Y-PSZ/Co(1-x)O interface. Amorphous regions and [111] faulting were also found in Co(1-x)O near Kirkendall pores, which can be rationalized by diffusion-induced amorphization and assembly of cation vacancies along close-packed [111] planes vulnerable to crystallographic shear, respectively. Y-PSZ particles were found to migrate-coalesce as corrugated slabs and rods at Co(1-x)O grain boundaries and junctions, respectively, when the composite with more Y-PSZ additive (Z(1)C(89)) was annealed.