Diffuse dielectric behaviour in Na0.5K0.5NbO3–LiTaO3–BiScO3 lead-free ceramics

Dielectric and piezoelectric properties are presented for lead-free piezoelectric compositions in the Na 0.5 K 0.5 NbO 3 –LiTaO 3 –BiScO 3 ternary system, focusing on the compositional join 0.98[(1 − x )(Na 0.5 K 0.5 NbO 3 )– x LiTaO 3 ]–0.02[BiScO 3 ]; 0 ≤ x ≤ 0.1. The end-member composition, 0.98Na 0.5 K 0.5 NbO 3 –0.02BiScO 3 has previously been reported to exhibit relatively high piezoelectric coefficients; the present paper examines changes in properties resulting from incorporation of LiTaO 3 . Measurements of relative permittivity versus temperature showed a Curie peak at ∼350 °C in x ≤ 0.02 samples. This peak broadened as the LiTaO 3 content increased from x = 0.02 to 0.03. At x = 0.05 and 0.07, the relative permittivity–temperature curve became even more diffuse, and a second peak occurred at ∼470 °C; transmission electron microscopy revealed this was the result of elemental segregation and the formation of a core–shell grain structure. Maximum values of d 33 piezoelectric charge coefficients were ∼200 pC/N in samples x = 0.01 and 0.02, for which dielectric and X-ray diffraction data inferred an orthorhombic–tetragonal phase transition close to room-temperature.