Large decrease of characteristic frequency of dielectric relaxation associated with domain-wall motion in Sb5+-modified (K,Na)NbO3-based ceramics

Abstract

The (K,Na)NbO3-based ceramics have drawn considerable attention as a type of promising lead-free piezoelectric materials in recent years. However, investigations on the dielectric dispersion spectra in the microwave range have rarely been conducted so far. Dielectric dispersion spectra of several representative (K,Na)NbO3-based ceramics were measured and compared in this study. An interesting physical phenomenon that the Sb5+-modified (K,Na)NbO3-based ceramics differ distinctly from those without Sb5+-modification in the aspect of characteristic frequency fp of dielectric relaxation associated with the domain-wall motion has been found. The former group shows the fp values in several tens of MHz at room temperature, whereas the latter group has generally the fp values of several GHz at least. For the Sb5+-modified (K,Na)NbO3-based ceramics, the change of fp with temperature follows roughly a thermally activated character. In contrast, the ones without Sb5+-modification exhibit a temperature-insensitive character in fp. Analysis showed that the results could be understood from the viewpoint of domain-wall vibration. It is speculated that a large change occurring in the damping constant due to the incorporation of Sb5+ is possibly the origin.