Investigation of the dielectric and piezoelectric properties of potassium sodium niobate ceramics close to the phase boundary at (K0.35Na0.65)NbO3 and partial substitutions with lithium and antimony

Potassium sodium niobate (KNN) piezoelectric ceramics and KNN substituted with lithium (Li+) and antimony (Sb5+) have been synthesized by the conventional solid state sintering method. This work focuses on the phase transition in the KNN system at potassium (K+) content of approximately 0.35. Therefore, K amount was altered from 0.31 to 0.35. Additionally, Li+ and Sb5+ were used for partial substitution (up to 8% for Sb) thereby enhancing the piezoelectric and dielectric properties. However, addition of Li+ and Sb5+ also lead to a decrease in both the Curie temperature (TC) and the first order phase transition temperature (TT-O) of the ceramics. Addition of more than 4 mol% of Li+ led to the formation of extra phases. The piezoelectric properties within the given composition range were found to be optimum at (K0.34Na0.64Li0.02)(Nb0.96Sb0.04)O3. A piezoelectric charge coefficient (d33*) of 404 pm/V for this composition was obtained from unipolar strain hysteresis measurements.