Investigation of fracture toughness of modified (KxNa1 − x)NbO3 lead-free piezoelectric ceramics

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, KIC, of the most widely studied (KxNa1 − x)NbO3 (KNN)-based lead-free ceramics modified with lithium, tantalum and antimony. The samples were produced through the conventional mixed-oxide route and the KIC 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 MPa m1/2 for (K0.48Na0.48Li0.04)NbO3, 0.8 ± 0.18 MPa m1/2 for (K0.5Na0.5)(Nb0.9Ta0.1)O3, 0.86 ± 0.04 MPa m1/2 for (K0.48Na0.48Li0.04)(Nb0.9Ta0.1)O3 and 1.06 ± 0.21 MPa m1/2 for (K0.48Na0.48Li0.04)(Nb0.86Ta0.1Sb0.04)O3 compositions. The microstructure, phase structure and dielectric constant values of the samples have been used to correlate the results of the KIC values.