Sintering of Lead-Free Piezoelectric Sodium Potassium Niobate Ceramics

Materials

Barbara Malič⁵  Jurij Koruza²  Jitka Hrešლk⁵  Janez Bernard¹  Ke Wang⁴  John G. Fisher³  Andreja Benლn⁵ 

[1] Slovenian National Building and Civil Engineering Institute, Dimičeva 12, Ljubljana 1000, Slovenia;Technische Universität Darmstadt, Alarich-Weiss-Str. 2, Darmstadt 64287, Germany;School of Materials Science and Engineering, Chonnam National University, Gwangju 500-757, Korea;State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China;Jožef Stefan Institute, Jamova cesta 39, Ljubljana 1000, Slovenia;

关键词: lead-free piezoelectric;    KNN;    sodium potassium niobate;    sintering;    microstructure;   

DOI  :  10.3390/ma8125449

来源: mdpi

【 摘 要 】

The potassium sodium niobate, K_0.5Na_0.5NbO₃, 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).

【 授权许可】

CC BY   
© 2015 by the authors; licensee MDPI, Basel, Switzerland.