Influence of Oxygen Vacancies on the Impedance Spectrum of Al₂O₃–Na_0.5K_0.5NbO₃ Composites

Abstract

Composites based on ferroelectric Na0.5K0.5NbO3 (NKN) and paraelectric Al2O3 were observed using impedance spectroscopy at different temperatures. This allowed for the evaluation of the conduction processes of the bulk and grain boundary, revealing the occurrence of interdiffusion and changes in the conductive properties. The effective conductivity decreased with the increase in Al2O3, which is due to the highly resistive nature of Al2O3. Interestingly, the activation energy for the bulk response increased from 0.87 ± 0.06 eV to approximately 1.12 ± 0.03 eV, and the activation energy of the grain boundary decreased from 1.26 ± 0.09 eV to 0.99 ± 0.09 eV. These observations of the activation energy revealed the interdiffusion of Al3+ ions, leading to the formation of oxygen vacancies in close vicinity to the grain boundary. As a result, the conduction path for charge carriers shifted to take place predominantly along the grain boundary.

Keywords

• impedance spectroscopy
• composites
• lead-free ferroelectrics