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

Astri Bjørnetun Haugen,Erling Ringgaard,Franck Levassort

doi:10.1088/2515-7639/ac0595

Abstract

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 d 33 values up to 171 pC N−1, and k t 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 (ϵ 33 T/ϵ 0 down to 182) resulted in record-high piezoelectric voltage constants (g 33 up to 101 mV m N−1), higher than previously reported for lead-free piezoelectric ceramics, as well as very high figure of merit (d 33 g 33 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.

Highlights

Piezoelectric materials are, due to their coupling of mechanical and electrical energy, applied in a vast range of technological devices
We show that the reasonable piezoelectric charge constant, combined with the very low dielectric permittivity results in materials with extremely high voltage constants and a high figure of merit for energy harvesting, and discuss the effects of texture on a wide set of parameters
The results presented here clearly demonstrate that textured KNNLTM can be prepared by templated grain growth from NaNbO3 templates, and that texture improves several key functional parameters

Summary

Introduction

Piezoelectric materials are, due to their coupling of mechanical and electrical energy, applied in a vast range of technological devices. The required material properties for piezoelectric energy harvesters depend strongly on the mode of operation This could either be harvesting at the resonant frequency of the piezoelectric material, typically at very high frequencies, where the figure of merit often is given as k2Qm, where k is the electromechanical coupling coefficient and Qm the mechanical quality factor [3, 4]. While such operation can harvest high amounts of energy, it requires a high frequency energy source and a harvester with a perfectly matched resonance frequency.

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Conclusion