Kirkendall porosity in barium titanate–strontium titanate diffusion couple

Inter-diffusion between perovskites BaTiO₃ and SrTiO₃ diffusion couple has been studied by determining the crystalline phases and analyzing the microchemistry and microstructure of undoped BaTiO₃–SrTiO₃ stacks sintered at 1250 °C in air. The Kirkendall effect manifested by: (1) an inter-diffusion zone containing (Ba_1−xSr_x)TiO₃ and (Sr_1−xBa_x)TiO₃ solid solutions, (2) the migration of the initial BaTiO₃–SrTiO₃ interface, and (3) the Kirkendall porosity was observed. The inter-diffused regions on both sides of the initial interface contain grains exhibiting the characteristic core–shell structure with distinctive solute contents between core and shell. TiO₂-rich polytitanates, notably Ba₄Ti₁₃O₃₀ and Ba₆Ti₁₇O₄₀ containing a minor amount of Sr from inter-diffusion, have been detected at the BaTiO₃ side near the initial BaTiO₃–SrTiO₃ interface. An analogy between the BaTiO₃–SrTiO₃ diffusion couple and Kirkendall's original α-brass-Cu couple is presented.