Hardening Effect on the Electromechanical Properties of KNN-Based Ceramics Using a Composite Approach

The high mechanical quality factor (Q (m)) of KNN-based ceramics is usually achieved by acceptordoping. However,this hardening effect has serious limitations due to the increasedmobility of oxygen vacancies under large electric fields and henceis difficult to use in high-power applications. In this work, thehardening mechanism is demonstrated by the development compositesof the 0.957(K0.48Na0.52)Nb0.94Ta0.06O3-0.04(Bi0.5Na0.5)ZrO3-0.003BiFeO(3) (KNNT-BNZ-BFO) matrix with the K4CuNb8O23 (KCN) phase using the two-stepball-milling method. A decrease in remnant polarization and dielectricconstant and an increase in resistivity and Q (m) are observed compared to that in the KNNT-BNZ-BFO sample.A high Q (m) of 160, Curie temperature, T (C), of 310 & DEG;C, and piezoelectric coefficient, d (33), of 330 pC/N can be obtained simultaneouslyin the composite with a 0.008 mole ratio of KCN. This can be explainedby the mechanical clamping effect of KCN due to strain incompatibilityand the domain wall pegging that traps charges at the KNNT-BNZ-BFO/KCNinterface. This composite approach is considered a general hardeningconcept and can be extended to other KNN-based ceramic systems.