Dislocation Loops in Pressureless‐Sintered Undoped BaTiO₃ Ceramics

Abstract

Dislocation loops in pressureless‐sintered undoped BaTiO3 ceramics have been analyzed by transmission electron microscopy. The Burgers vector of the loops and its sense b=+1/2[010] were determined using the g·b=0 invisibility criteria, combined with the inside–outside contrast technique using (g·b)sg>0 or<0, keeping the deviation parameter sg>0. The edge‐vacancy nature was further ascertained by determining the loop habit plane normal n=[010]. Weak‐beam dark‐field imaging reveals that loops contained no stacking fault fringes; they are edge‐vacancy partial dislocation loops lying in {020} or {010} where parts of the TiO2 or BaO layer are vacant. It is suggested that the extrinsic defects of both cations and oxygen vacancies generated by non‐stoichiometry have condensed during sintering in air and are responsible for the formation of such vacancy loops.

High temperature creep‐mediated functionality in polycrystalline barium titanate

“…The individual dislocations in Figure D and the dislocation structures in (F) verify that it is possible to introduce dislocations by plastic deformation of BaTiO 3 . Previous TEM analyses have demonstrated that different types of dislocations can be induced in BaTiO 3 ‐based materials . Figure D reveals typical dislocations loops with scallops along the dislocation line .…”

“…Suzuki et al argued that these loops arise due to vacancy condensation and require the presence of Schottky defects (eg, ) . Additionally, it was proven that dislocations can adorn domain walls . and that the density of the dislocation loops can be influenced by oxygen partial pressure …”

Intragranular Voids and dc Degradation in (CaO+MgO) Codoped BaTiO3Multilayer Ceramic Capacitors

“…In Al alloys, thermal vacancies are known to condense to prismatic dislocation loops upon quenching to room temperature 29 . Indeed, vacancy loops in BaTiO 3 were often found in MLCC chips, 30 in undoped BaTiO 3 , 31 and in MgO doped BaTiO 3 32 sintered in air. Two types of loops are formed with an identical Burgers vector b =1/2 〈010〉 31 via the condensation of (i) and (i.e., vacant BaO‐layer), and (ii) and (i.e., vacant TiO 2 layer) 30 .…”

“…Indeed, vacancy loops in BaTiO 3 were often found in MLCC chips, 30 in undoped BaTiO 3 , 31 and in MgO doped BaTiO 3 32 sintered in air. Two types of loops are formed with an identical Burgers vector b =1/2 〈010〉 31 via the condensation of (i) and (i.e., vacant BaO‐layer), and (ii) and (i.e., vacant TiO 2 layer) 30 . Vacancies in the stoichiometric composition are required at the sites where loops are formed, and the slower moving species (Ba 2+ or Ti 4+ ) is rate‐controlling kinetically in forming loops.…”

“…Thus, even if those created by reducing sintering 22,23 are not considered, more oxygen vacancies expected from the dissolved Mg 2+ would make the inverse Schottky reaction for vacancy condensation () to form voids more favorable. When its concentration is not sufficient to warrant the inverse Schottky reaction, apart from condensing to dislocation loops, 30–32 can either combine with substitutional defects to form defect associates 1,27,36,37 in core shell grains, 1 or exists as individual defect distributed randomly in the crystal. It is the individual oxygen vacancies in a dilute solid solution when driven to migrate by an electric field during demixing 5–7 are primarily responsible for dc degradation.…”