The unusual case of plastic deformation and high dislocation densities with the cold sintering of the piezoelectric ceramic K0.5Na0.5NbO3

Koki Nakagawa, Masato Iwasaki, Zhongming Fan, James Roscow, Clive Randall

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K0.5Na0.5NbO3 (KNN) can be readily densified using the cold sintering process, but despite observing high relative permittivity, the ferroelectric hysteresis is strongly suppressed along with a major suppression in the all-important piezoelectric properties. In this study, KNN is fabricated using a NaOH+KOH transient flux under a uniaxial pressure of 400 MPa and heating to 300 °C for 2 h to drive densification to 93% theoretical. It is only after a secondary heat treatment that we observe improvements of the ferroelectric hysteresis and piezoelectric properties. From a detailed structural-property-processing study using analytical transmission electron microscopy (TEM), X-ray line broadening and high field dielectric characterization methodologies we conclude that there is an unusual in-situ plastic deformation process that takes place in addition to the densification under the cold sintering process. High densities of dislocations within grains were observed that lead to multiple pinning sites that impact both the intrinsic and extrinsic contributions to the high field dielectric and piezoelectric properties. Annealing significantly reduced the dislocation density in the highly defective crystallites, observed directly from the TEM and from the sharpening of the X-ray diffraction peaks, resulting in piezoelectric and ferroelectric properties that approached those of conventionally sintered KNN.
Original languageEnglish
Pages (from-to)4015-4020
Number of pages6
JournalJournal of the European Ceramic Society
Issue number9
Early online date24 Feb 2023
Publication statusPublished - 28 Mar 2023

Bibliographical note

Supplementary data associated with this article can be found in the
online version at doi:10.1016/j.jeurceramsoc.2023.02.057.

Funding Information:
Koki Nakagawa would like to express his gratitude to NGK SPARK PLUG CO., LTD . for supporting his research at the Pennsylvania State University . James I. Roscow is grateful to the EPSRC for financial support ( EP/V002155/1 and EP/V011332/1 ). Clive Randall and Zhongming Fan would like to thank the support from partial support from the AFOSR FA9550–19-1–0372 .


  • Cold sintering process
  • K Na NbO ceramics
  • Piezoelectric
  • Plastic deformation

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry


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