Cation vacancy defect in modified barium titanate ferroelectric ceramics

Abstract

Development of advanced technologies for electronic applications, particularly aiming to increase energy efficiency and sustainability, are increasing in demand for regular usage. A majority of this development involves improvement of material's properties. Researcher has been continuously studied and developed new electronic material. Ferroelectric ceramic is one of many materials that is of interest, for example, lead-based (e.g. Pb(Mg₁/₃Nb₂/₃)O₃: PMN) and lead-free (e.g. Ba(Zr,Ti)O₃: BZT) materials. It is, however, known that the RoHS (Restriction of Hazardous Substances Directive) listed Lead (Pb) as one of the hazardous materials and is restricted for using in many electronic applications. Therefore, the development of lead-free materials has increased in attention and there is many more aspects of research to be explored. The electrical properties of relaxor ferroelectric ceramics, especially dielectric and ferroelectric behaviors, are improved from normal ferroelectric ceramic, which led to the usage of these materials in various applications such as capacitors and piezoelectric devices. A majority of researches focuses on fundamental understanding of relaxor behavior both experimentally and theoretically as well as device development based on these materials. In fabrication process, it is common to find defects in polycrystalline materials, which can be in a range of atomicscale to micro-scale. These defects play major roles in controlling electrical properties of the ceramics. In some applications, defects can be advantage as to improve the properties of the devices. On the other hand, properties of devices can be deteriorated by the present of defects leading to electrical fatigue and failure of devices under extreme conditions. It is, therefore, important to understand how cation vacancy defect affects electrical properties of modified barium titanate ferroelectric ceramics. The effect of Acation non-stoichiometry on the electrical properties of barium strontium titanate ceramics is an interesting topic of investigation. This study examined the stoichiometric, Ba-excess, Ba-deficient, Sr-excess and Sr-deficient compositions of (Ba₀.₈Sr₀.₂)Ti0₃ ceramics. A-cation non-stoichiometry of (Ba₀.₈₀Sr₀.₂₀)TiO₃ ceramics affected dielectric properties differently. The Ba- and Sr-excess compositions decreased dielectric constant at Tmax while still maintaining broad phase transition characteristics. In contrast, dielectric constant increased in the Ba- and Sr-deficient compositions. The characteristics of electrical conduction are different at high temperatures when Ba- and Sr-deficiency is introduced to the dielectrics. Ti⁴⁺ state for the Ba-deficient composition is maintained. However, Ti⁴⁺state partially changes to Ti³⁺ state, giving rise in the polaron hopping conduction process for Sr-deficient composition. Therefore, this study shows that minor deviation of A-cation from stoichiometry can induce a different conduction process while maintaining the dielectric permittivity characteristics.