Space-charge relaxation and electrical conduction in K_0.5Na _0.5NbO₃ at high temperatures

Sodium potassium niobate K_0.5Na_0.5NbO₃ (KNN) ceramic was synthesized by a solid-state technique. The Xray diffraction of the sample at room temperature showed a monoclinic phase. The real part (ε") and imaginary part (ε') of dielectric permittivity of the sample were measured in a frequency range from 40 Hz to 1 MHz and in a temperature range from 350 to 850 K. The ε' deviated from Curie-Weiss law above 702 K, due to additional dielectric contributions resulting from universal dielectric response and thermally activated space charges at high temperatures. This anomaly arose from a Debye dielectric dispersion that slowed down following an Arrhenius law. We have established a link between the dielectric relaxation and the conductivity.