“…a-brass-Cu [8], Ni-Ti [9], the migration of all species, including both cations and oxygen, across the interface in the inter-diffusion of such complex oxides [6] is required for the effect to be realized. However, no observation of Kirkendall porosity by scanning electron microscopy (SEM) was reported by Butler et al [5] when only inter-diffusion of Ca 2+ and Sr 2+ in CaTiO 3 and SrTiO 3 lattice, respectively, via a vacancy mechanism was found; the former cation was the faster diffusing species. Although Kirkendall-like porosity was again not detected experimentally in another study [7], it was thought to have retarded densification in a sintered BaTiO 3 -SrTiO 3 powder mixture.…”