Mechanism of densification in low-temperature FLASH sintered lead free potassium sodium niobate (KNN) piezoelectrics


Lead-free potassium sodium niobate (K0.5Na0.5NbO3, KNN) piezoelectric ceramics have been densified at temperatures lower than 300 degrees C using atmosphere-water assisted FLASH sintering. Transmission electron microscopy (TEM) studies revealed amorphous phase at grain boundaries that resulted from surface melting of the cuboid particles in the presence of segregated impurities. We propose that preferential surface melting of the primary particles is induced in conductive channels of open pores in which water is adsorbed. This creates a network of pathways for the electric current. The resulting liquid phase induces fast densification through sliding of grain boundaries and viscous flow of the liquid driven by minimisation of surface energy. Finite Element Modelling (FEM) revealed that current density and Joule heating were also influenced by the geometry of contact between the cuboid KNN particles with vertex to vertex inducing the maximum current density and consequently creating the greatest volume of amorphous phase in adjacent pores. The lowest current density was predicted for face to face contacts, resulting in only a thin amorphous layer between grains.



subject category

Materials Science; Physics


Serrazina, R; Dean, JS; Reaney, IM; Pereira, L; Vilarinho, PM; Senos, AMOR

our authors


This work is financed by Portugal 2020 through European Regional Development Fund (ERDF), in the frame of Operational Competitiveness and Internationalization Programme (POCI), in the scope of the project FLASH sintering of lead free functional oxides towards sustainable processing of materials for energy and related applications- FLASH, POCI-01-0247-FEDER-029078. This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, FCT Ref. UID/CTM/50011/2019, financed by national funds through the FCT/MCTES. Ricardo Serrazina acknowledges FCT for financial support (SFRH/PD/BD/128411/2017). Dr J. S. Dean and Professor I. M. Reaney acknowledge the support of EPSRC grants (EP/L017563/1 and EP/P019919/1).

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