Effect of Intrinsic Nb⁵⁺ Vacancy on Dielectric and Polarization Behaviors of KSr₂Nb₅O₁₅: First-Principles Investigation

The Nb in the structure of ferroelectric KSr₂Nb₅O₁₅ (KSN) is designated as Nb1 or Nb2 as it is surrounded by differing amounts of oxygen atoms. The dielectric properties and spontaneous polarization intensity of KSN with different Nb⁵⁺ vacancies are studied using first-principles calculations and the influence mechanism of intrinsic cation vacancies on the dielectric properties and spontaneous polarization intensity of KSN is clarified. The dielectric constants and polarization responses to the materials are different when vacancy is formed at these two types of Nb sites, respectively; vacancy at the Nb1 site increases the dielectric constant, whereas vacancy at the Nb2 site decreases it. Furthermore, the experimental results support the effects of Nb⁵⁺ vacancy on the polarization behavior of the material, including polarizability and polarization intensity. This study provides a theoretical foundation for better understanding and improving the dielectric properties and polarization behavior of tungsten bronze structure ferroelectrics.