Dielectric Properties of (Bi0.5K0.5)ZrO3 Modified (K0.5Na0.5)NbO3 Ceramics as High-Temperature Ceramic Capacitors

(1 - x)K0.5Na0.5NbO3-x(Bi0.5K0.5)ZrO3 [abbreviated as (1 - x)KNN-xBKZ, 0 <= x <= 0.08] lead-free ceramics have been fabricated by a solid-state processing route. Based on the x-ray diffraction data and temperature-dependent dielectric characteristics, an orthorhombic phase for x <= 0.03 and single rhombohedral one for x >= 0.05 at room temperature were determined. The cell volume firstly increases, then decreases and finally increases with increasing BKZ, depending on ionic size and crystallographic structure. For the sample of x = 0.05, a temperature-stable high permittivity (similar to 1736 +/- 15%) along with low dielectric loss tangent (<= 5%) is recorded from 158 degrees C to 407 degrees C. In addition, the activation energies of dielectric relaxation and dc conductivity at high temperatures were characterized by impedance spectroscopy. A combined effect of lattice distortion and oxygen vacancies on the magnitude of activation energies was discussed.