Textured, lead-free piezoelectric ceramics with high figure of merit for energy harvesting

Piezoelectrics are key materials for energy conversion, for example in ultrasound transducers and energy harvesters. This work presents the synthesis and characterization of the lead-free piezoelectric composition (Li0.06(K0.52Na0.48)0.94)(Nb0.71Ta0.29)O3 doped with 0.25 mol% Mn (KNNLTM) as textured ceramics. Templated grain growth from NaNbO3 platelet templates aligned by tape casting was used to introduce texture, and after sintering for 14 h at 1100 °C this produced up to 84% (100)pc grain orientation. After high temperature poling, the textured samples exhibit reasonable piezoelectric response with d33 values up to 171 pC N-1, and kt values of 0.35, which is 71% of the response obtained in a single crystal of the same composition. The low relative dielectric permittivity of the textured and high temperature-poled KNNLTM (ϵ33 T/ϵ0 down to 182) resulted in record-high piezoelectric voltage constants (g33 up to 101 mV m N-1), higher than previously reported for lead-free piezoelectric ceramics, as well as very high figure of merit (d33g33 up to 16 × 10-12 m3 J-1) for non-resonant energy harvesting in compression. These numbers make the textured KNNLTM materials of this work highly promising for use in thickness mode, non-resonant piezoelectric energy harvesters.