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 (Ba1−xSrx)TiO3 and (Sr1−xBax)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.