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Open AccessFeature PaperReview

Sintering of Lead-Free Piezoelectric Sodium Potassium Niobate Ceramics

Jožef Stefan Institute, Jamova cesta 39, Ljubljana 1000, Slovenia
Jožef Stefan International Postgraduate School, Jamova cesta 39, Ljubljana 1000, Slovenia
Technische Universität Darmstadt, Alarich-Weiss-Str. 2, Darmstadt 64287, Germany
Slovenian National Building and Civil Engineering Institute, Dimičeva 12, Ljubljana 1000, Slovenia
State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
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;
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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MDPI and ACS Style

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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