Dopants and oxygen vacancy migration mechanism in temperature-stable (Ba, Ca)TiO3-based ceramics

The migration of dopants and oxygen vacancy (VO) significantly affect the temperature stability and insulation degradation behavior of BaTiO3-based dielectric ceramics. In this work, the improved dielectric properties and reliability are achieved in (Ba, Ca)TiO3 (BCT)-based ceramics due to the intriguing effect of Ca substitution. Theoretical calculations and experiments reveal the underlying mechanisms in the migration of dopants and VO. The migration barrier of dopants is increased by ∼0.02 eV or less due to the lattice shrinkage, while it is decreased by ∼0.5 eV due to the interatomic space expansion effect caused by the small size of Ca. Thus, the core–shell structure is more susceptible in BCT-based ceramics with higher Ca content. The VO is confirmed to be more stable near the Ca ion, forming the [CaBa-VO]·· defect complex. However, the migration barrier is significantly decreased among the first nearest O sites of Ca due to the enlarged space near Ca ion. Thus, the activation energy of VO and insulation degradation behavior are improved in BCT-based ceramics with moderate Ca content but deteriorate with high content, in which the intragranular migration channels with the low barrier are formed. The present results reveal the significant effect of Ca substitution on the migration of dopants and VOs, and further on the dielectric temperature stability and reliability.