Control of interface migration in melt-infiltrated niobium-doped strontium titanate by solute species and atmosphere

Abstract

The solid/liquid interface migration of niobium-doped strontium titanate (SrTiO3) has been investigated by using barium and calcium solute sources in the form of a Cu-Ba-Ca-O liquid, The solubilities of barium and calcium in SrTiO3 that is in equilibrium with Cu-Ba-Ca-O melts can be determined by measuring the solute concentration in the migrated Sr(Ba,Ca)TiO3 regions of SrTiO3 grains, No interface migration is observed for a certain composition range of Cu-Ba-Ca-O infiltrant, For SrTiO3 specimens that have been sintered in air, the zero driving force for the interface migration is found at a Ba:Ca ratio of -0.75 in Sr(Ba,Ca)TiO3 solid solution. This value is in good agreement with a predicted value of zero coherency strain in a thin diffusional Sr(Ba,Ca)TiO3 layer on bulk SrTiO3, For the specimens that have been sintered in 5H(2)-95N(2), however, a zero driving force results when the ratio is similar to 0.84, The difference between the value for the specimens sintered in air and that for the specimens sintered in 5H(2)-95N(2) is attributed to the change in defect concentration,ia the change in atmosphere. The estimated difference in the lattice parameters of SrTiO3 sintered in air and those of SrTiO, sintered in 5H(2)-95N(2) is similar to 1.8 x 10(-3) Angstrom (similar to 1.8 x 10(-2) mn), The difference in lattice parameters has been further confirmed by using synchrotron X-ray scattering experiment, which has revealed the lattice parameter to be 3.9053 Angstrom (0.39053 nm) in air and 3.9070 Angstrom (0.39070 mm) in 5H(2)-95N(2).