Sintering of lead-free piezoelectric sodium potassium niobate ceramics

Barbara Malič*, Jurij Koruza, Jitka Hreščak, Janez Bernard, Ke Wang, John G. Fisher, Andreja Benčan

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review


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).

Original languageEnglish
Pages (from-to)8117-8146
Number of pages30
Issue number12
Publication statusPublished - 2015
Externally publishedYes


  • KNN
  • Lead-free piezoelectric
  • Microstructure
  • Sintering
  • Sodium potassium niobate

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics


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