Speaker
Description
In order to substitute lead zirconate-titanate (PZT) based materials, due to its poisonous nature, some promising piezoelectric and friendly environment compounds are attracting growing attention, namely KxNa(1-x)NbO3 [1]. For the case of x=0.5, K0.5Na0.5NbO3 (KNN), the high-temperature cubic symmetry changes to a non-symmetric ferroelectric tetragonal structure at T3=700 K, becoming orthorhombic at T2=465 K, and finally stabilizing in a rhombohedral symmetry below T1=135 K [2]. Recently, theoretical calculations have predicted piezoelectric response enhancement when T3 become closer to T2 [3], in which sintering conditions could play an important role [4,5].
In this work, we revisit the phase transition sequence and the effect of the sintering process on the structure, lattice dynamics, and dielectric/polar properties of KNN ceramics prepared by conventional sintering, spark plasma sintering, and spark plasma texturing. From a comparative analysis of the overall experimental obtained results, we have observed that the phase transition sequence includes an unreported structural and polar phase at low temperatures, independently on the processing method. Moreover, apparent changes of the stability temperature interval of the different phases have been ascertained. The dielectric strength and the emergence of a dielectric relaxation phenomenon are also noticeably dependent on the processing method, which can be understood as an effect of the different grain size. The results here reported clearly point out towards the possibility to change physical properties following different sintering routes to improve device performance.
References
[1] I. Coondoo et al., J. Advanced Dielectrics, 03, 1330002 (2013)
[2] B. Orayech et al., J. Appl. Cryst., 48, 318-333 (2015)
[3] D. Damjanovic, Appl. Physics Letters, 97, 062906 (2010)
[4] R. Pinho et al., Appl. Mater. Today 19, 100566 (2020)
[5] M.M. Gomes et al., Ceram. Int., 47, 8308-8314 (2021)
