Piezoelectric ceramics are used widely as transducers in novel applications such as acoustic sensors[1], structural health monitoring[2], and energy harvesting[3]. Among piezoelectric ceramics, Lead Zirconate Titanate (PZT) is used widely due to the high piezoelectric coefficient, in the ranges of 300 to 600 pC/N. However, with the increasing concern about environmental and health problems, tremendous efforts have been devoted to the exploration of lead-free substitutions.
 
Potassium sodium niobate (KNN)-based materials are promising lead-free candidates for replacing PZT-based piezoelectric materials. Chemical modification of KNN-based compositions has been a fundamental approach for achieving high performance comparable to that of PZT, by shift of different phase boundaries, i.e., O-T and R-O, near to room temperature [4] for imitating the morphotropic phase boundary (MPB) in PZT[5]. The main disadvantages, including for solid solutions, are related to synthesis problems: i) decomposition at a relatively low temperature (1040 °C),(ii) the volatility of potassium, which makes it difficult to control stoichiometry, iii) the appearance of secondary phases (losses of K) which make the materials highly hygroscopic and very unstable with respect to humidity. As for PZT, the sinterability of KNN materials can be improved by using different sintering aids, such as LiF[6], CuO[7], ZnO[8], MnO[9]. The expected advantages of sintering aids are: the improvement of the density, lower the sintering temperature and enhancing the piezoelectric properties.
 
In this work, a well densified KNN composition doped with Li, Sb, Ba, Zr prepared by solid state method, with a d33 of 263 pC/N and a kp of 43% are presented. In order to evaluate the influence of the sintering aids, several modified KNN-LS BZ ceramics with the various ratio of CuO and MnO2 were prepared, and the piezoelectric properties will be described.
References:
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[2] Y. Yang and al., Sensors 10 (2010) 5193-5208
[3] D. Shin and al., Ceram. Int. 41 (2015) S686–S690
[4] A. Borta Boyon, M Pham-Thi, IEEE ISAF-FMA-AMF-AMEC-PFM Joint Conference, 2019
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[9] F. Rubio-Marcos, and al., Journal of Alloys and Compounds 509,8804– 8811, (2011)