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

Abstract 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 x Na 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 K IC values were determined to be 0.48 ± 0.18 MPa m 1/2 for (K 0.48 Na 0.48 Li 0.04 )NbO 3 , 0.8 ± 0.18 MPa m 1/2 for (K 0.5 Na 0.5 )(Nb 0.9 Ta 0.1 )O 3 , 0.86 ± 0.04 MPa m 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 MPa m 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.