Effect of potassium content on the dielectric and electrical properties of sodium potassium niobate ceramics

(K_xNa_1-x) NbO3 ceramics or KNN is considered as one of the most promising candidates for lead-free piezoelectric applications, because of its high Curie temperature and good electrical properties. However, it is well known that dense and well-sintered KNN ceramics are very difficult to obtain by conventional sintering process because of the high volatility of alkali elements at high temperatures. The major strategy to overcome this problem is simply adding excess alkali metals in the starting composition. KNN ceramics with potassium excess were prepared by high temperature solid state reaction technique. Effect of K excess on the phase structure and electrical properties of KNN ceramics were investigated. The results showed that the single phase orthorhombic perovskite structure was obtained in ceramics. Ferroelectric-paraelectric phase transition temperature was about 370 °C for all the samples. The dielectric permittivity was maximized, the dielectric loss was a minimum and the relative density was found to reach 95% of theoretical density for K content= 53% in KNN system. Impedance study shows the non-Debye type temperature of relaxation phenomenon in the system. Above the ferroelectric paraelectric phase transition temperature, the electrical conduction is governed by the thermal excitation of carriers from oxygen vacancies exhibiting NTCR behavior.