Defect-driven conductivity behavior in lead-free KNN-based ceramics

Abstract

Defect-driven properties of lead-free piezoelectric materials have become the focus of research as a result of in-depth investigations into such materials. Here, we pay special attention to the conductivity mechanism of 0.91K0.5Na0.5NbO3–0.05Ag1 − xNaxSbO3–0.04Bi0.5Na0.5ZrO3 ceramics. The charge carrier concentration induced by defects, which exerts an effect on conductivity, displays different mechanisms under different temperatures. By analyzing the energy band diagram, we identify the carriers to be oxygen vacancy and electron, which are related to the dielectric relaxation. In addition, by means of comparison between the Fermi level and the donor ionization level, we find that parts of oxygen vacancies are single-ionized in the low temperature region and this is attributed to the Fermi level approaching the first ionization energy of oxygen vacancies, while the ionized electrons emanate from approximately the first ionization and from a part of the second ionization in the high temperature region due to the Fermi level being far below the first ionization energy of oxygen vacancies and close to the second ionization energy. We hope that the analysis of the defect and origin of ionized electrons will help to further enhance the electrical properties in K0.5Na0.5NbO3-based ceramics.