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Phase transition behaviour and dielectric properties of Na_0.5K_0.5NbO₃-LiTaO₃-LiSbO₃ lead-free piezoceramic

Pornsuda Bomlai^a,c,*, Supasarote Muensit^b,c, Steven J. Milne^d

 
ABSTRACT:     Lead-free piezoelectric ceramics have attracted considerable attention as new piezoelectric materials for replacing Pb(Zr,Ti)O₃ (PZT)-based ceramics because of environmental protection reasons. Among lead-free piezoelectric systems, the ternary system of Na_0.5K_0.5NbO₃-LiTaO₃-LiSbO₃ has proven to be an outstanding lead-free piezoceramic with properties almost comparable to undoped PZT. In this study, addition of LiSbO₃ to the 0.95Na_0.5K_0.5NbO₃-0.05LiTaO₃ lead-free piezoceramic composition showed a change from an orthorhombic to a tetragonal crystal system in samples prepared by reaction-sintering. The limit of solid solution along the compositional join, (0.95−x)Na_0.5K_0.5NbO₃-0.05LiTaO₃-xLiSbO₃, occurred at x∼0.06. Differential scanning calorimetry analysis and measurements of dielectric constant as a function of temperature indicated broad Curie peaks from which it was inferred that the samples were not chemically homogeneous. Curie temperatures decreased from ∼425 °C for x=0, to ∼345 °C for the limiting x=0.06 composition. Improvement of dielectric properties was obtained for LiSbO₃ modified samples. Microstructures exhibited secondary recrystallization, with LiSbO₃ addition giving rise to a small reduction in average grain size.

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* Corresponding author, E-mail: ppornsuda@yahoo.com

Received 22 May 2009, Accepted 27 Aug 2009