Dislocation loop formation in nonstoichiometric (Ba,Ca)TiO3 and BaTiO3 ceramics

Dislocation loops observed in nonstoichiometric and stoichiometric (Ba,Ca)TiO3, and in stoichiometric BaTiO3 sintered in a reducing atmosphere, were characterized by conventional transmission electron microscopy (TEM) under two-beam conditions and high-resolution TEM atomic structure analysis. Dislocation loops mostly lay on {100} planes with Burgers vectors of type [100]. The dynamic behavior of these dislocation loops during the electron beam irradiation (EBI), however, was classified into two different types of dislocation loops: in A-site-excess (Ba,Ca)TiO3, contrasts of dislocation loops faded completely away; in BaTiO3 and B-site-excess (Ba,Ca)TiO3, fine-line contrasts remained. Dislocation loops with Burgers vectors of type 1/2(100) and the resultant crystallographic shear (CS) structure with a displacement vector of type 1/2[110] after EBI were proposed to interpret residual line images. Disappearance of these line images in A-site-excess (Ba,Ca)TiO3 strongly suggests preferential Ca ion site occupancy at the CS structure.