Electrical conduction and dielectric relaxation mechanisms in the KNN-based ceramics

Abstract

Multilayer ceramic actuators with a base metal internal electrode are in great demand because of their high voltage-driven displacement. Thus, the piezoelectric materials should be sintered in low oxygen partial pressure. The (Li, Ta, Sb)-doped (K,Na)NbO3 (KNN)-based ceramics are heat-treated in O2, air, N2, and 99 vol. % N2/1 vol. % H2 mixture gas at 300 °C in this study to identify the predominant charge carriers by defect chemistry. By analyzing electrical conduction and dielectric relaxation mechanisms, the dominant charge carriers in the ceramics are electrons and oxygen vacancies at low (<450 °C) and high temperature (>500 °C), respectively. In addition, the defect concentration in the ceramics increases with the decreasing oxygen partial pressures, and the change is more evident in the presence of H2 gas. Correspondingly, the electrical properties slightly degrade with the decreasing oxygen partial pressure and severely degrade in the N2/H2 mixture gas. Therefore, the (Li, Ta, Sb)-doped KNN-based ceramics with an n-type conduction mechanism are difficult to sinter in a reducing atmosphere. In order to cofire with base metal electrodes, the p-type conduction should be designed by doping the KNN ceramic in the future for industrial application.