Effect of Eu Doping on the Structural, Electrical, and Dielectric Properties of K0.5Na0.5NbO3 Ceramics for High-Temperature Capacitor Applications

The structural and dielectric properties of Eu-doped K0.5Na0.5NbO3 (KNN) ceramics were investigated as a potential candidate for use in high-temperature capacitors with working temperature beyond 200A degrees C. x-Ray diffraction results showed that tetragonal and cubic structure distortions occurred for low- and high-concentration doping, respectively. With increase of Eu content, the dielectric anomaly of the tetragonal-cubic transition was depressed and shifted to low temperature, while the temperature of the orthorhombic-tetragonal transition remained unchanged. A dielectric relaxation associated with oxygen vacancies was detected in the paraelectric phase region. The activation energy of oxygen vacancies depended on the Eu concentration and the defect compensation mechanism. KNN doped with 3 mol% Eu (KNN3Eu) showed good dielectric temperature stability (+/- 10%) with relatively high permittivity (> 1800 at 225A degrees C) over the temperature range from 119A degrees C to 495A degrees C, representing a good starting point for development of high-temperature capacitor materials.