Effects of SrTiO3 Modification on the Piezoelectric and Strain Properties of Lead-Free K0.5Na0.5NbO3-Based Ceramics

Abstract

Lead-free (1−x) K0.5Na0.5NbO3−xSrTiO3 (KNN-100xST) piezoelectric ceramics were prepared using a conventional solid-state reaction method to investigate their phase-transition behavior and electrical properties. SrTiO3 modification is known to improve the piezoelectric properties and sinterability of lead-free KNN ceramics. Previous studies on SrTiO3-modified KNN ceramics have mainly focused on enhancements to the dielectric and piezoelectric properties using an orthorhombic–tetragonal phase transition concept. However, the electromechanical strain behavior near this phase boundary remains challenging. In this work, a polymorphic phase boundary between the orthorhombic and tetragonal phases was found at 5 mol% of SrTiO3 content, where an enhanced piezoelectric constant (d33) was observed. In addition, normalized strain (d*33) was obtained from the unipolar strain at 4 kV/mm, which reached the highest value of 210 pm/V in KNN-5ST ceramics.