Controlling of the polymorphic phase transition on lead-free piezoelectric Li0.08(Na0.52+xK0.48)0.92NbO3 ceramics

The polymorphic phase transition (PPT) from tetragonal to orthorhombic symmetry was tailored in lead-free piezoelectric ceramics Li0.08(Na0.52+xK0.48)0.92NbO3 (LN0.52+xKN) by controlling excess Na content, which is opposite to the usually reported orthorhombic–tetragonal phase transition. The grain growth was accelerated by adding excess Na, resulting in an increased grain size from 2–3 μm to 7–8 μm and a bimodal grain size distribution for samples x=0.015–0.04. The optimized piezoelectric properties with, i.e. d33=226 pC/N and kp=36.8% were obtained in sample x=0.04 due to the PPT effect. The corresponding TC, Pr, and Er were 468 °C, 25.5 μC/cm2 and 1.20 kV/mm, respectively.