Investigation of fracture toughness of modified (K_xNa_(1-x))NbO_3 lead-free piezoelectric ceramics

摘要

While most of the previous studies have focused on the processing and electrical properties of KNN-based ceramics, very little research has been carried out to evaluate their mechanical behavior. This work presents for the first time an examination of the fracture toughness, K_(IC), of the most widely studied (K_xNa_(1-x))NbO_3 (KNN)-based lead-free ceramics modified with lithium, tantalum and antimony. The samples were produced through the conventional mixed-oxide route and the K_(IC) values were measured using the single edge V-notched beam (SEVNB) method under four-point bending. The mean KIC values were determined to be 0.48 ± 0.18 MPam~(1/2) for (K_(0.48)Na_(0.48)Li_(0.04))NbO_3, 0.8 ± 0.18 MPam~(1/2) for (K_(0.5)Na_(0.5))(Nb_(0.9)Ta_(0.1))O_3, 0.86 ± 0.04 MPam~(1/2) for (K_(0.48)Na_(0.48)Li_(0.04))(Nb_(0.9)Ta_(0.1))O_3 and 1.06 ± 0.21 MPam~(1/2) for (K_(0.48)Na_(0.48)Li_(0.04))(Nb_(0.86)Ta_(0.1)Sb_(0.04))O_3 compositions. The microstructure, phase structure and dielectric constant values of the samples have been used to correlate the results of the K_(IC) values.