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Open AccessFeature PaperReview

Sintering of Lead-Free Piezoelectric Sodium Potassium Niobate Ceramics

1
Jožef Stefan Institute, Jamova cesta 39, Ljubljana 1000, Slovenia
2
Jožef Stefan International Postgraduate School, Jamova cesta 39, Ljubljana 1000, Slovenia
3
Technische Universität Darmstadt, Alarich-Weiss-Str. 2, Darmstadt 64287, Germany
4
Slovenian National Building and Civil Engineering Institute, Dimičeva 12, Ljubljana 1000, Slovenia
5
State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
6
School of Materials Science and Engineering, Chonnam National University, Gwangju 500-757, Korea
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Academic Editor: Lorena Pardo
Materials 2015, 8(12), 8117-8146; https://doi.org/10.3390/ma8125449
Received: 16 October 2015 / Revised: 16 November 2015 / Accepted: 20 November 2015 / Published: 1 December 2015
(This article belongs to the Special Issue Piezoelectric Materials)
The potassium sodium niobate, K0.5Na0.5NbO3, solid solution (KNN) is considered as one of the most promising, environment-friendly, lead-free candidates to replace highly efficient, lead-based piezoelectrics. Since the first reports of KNN, it has been recognized that obtaining phase-pure materials with a high density and a uniform, fine-grained microstructure is a major challenge. For this reason the present paper reviews the different methods for consolidating KNN ceramics. The difficulties involved in the solid-state synthesis of KNN powder, i.e., obtaining phase purity, the stoichiometry of the perovskite phase, and the chemical homogeneity, are discussed. The solid-state sintering of stoichiometric KNN is characterized by poor densification and an extremely narrow sintering-temperature range, which is close to the solidus temperature. A study of the initial sintering stage revealed that coarsening of the microstructure without densification contributes to a reduction of the driving force for sintering. The influences of the (K + Na)/Nb molar ratio, the presence of a liquid phase, chemical modifications (doping, complex solid solutions) and different atmospheres (i.e., defect chemistry) on the sintering are discussed. Special sintering techniques, such as pressure-assisted sintering and spark-plasma sintering, can be effective methods for enhancing the density of KNN ceramics. The sintering behavior of KNN is compared to that of a representative piezoelectric lead zirconate titanate (PZT). View Full-Text
Keywords: lead-free piezoelectric; KNN; sodium potassium niobate; sintering; microstructure lead-free piezoelectric; KNN; sodium potassium niobate; sintering; microstructure
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Malič, B.; Koruza, J.; Hreščak, J.; Bernard, J.; Wang, K.; Fisher, J.G.; Benčan, A. Sintering of Lead-Free Piezoelectric Sodium Potassium Niobate Ceramics. Materials 2015, 8, 8117-8146.

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