Phase transition, dielectric and piezoelectric properties of lead-free piezoelectric (K1/2Na1/2)NbO3 - Bi(Zn2/3Nb1/3)O3 ceramics

The lead-free piezoelectric ceramics on the binary system of (1-x)(K1/2Na1/2)NbO3-xBi(Zn2/3Nb1/3)O3 [(1-x)KNN-xBZnN]; x = 0.01-0.10 were fabricated by the solid state reaction method. The structure and phase transition were determined by X-ray diffraction.The results of XRD patterns suggested that Bi(Zn2/3Nb1/3)O3 completely diffuse into the (K1/2Na1/2)NbO3 lattices to form a solid solution. The crystal structure was in an orthorhombic phase for x ≤ 0.01. When reaching 0.01 < x ≤ 0.07, crystal structure became a rhombohedral phase and transformed to a pseudo-cubic structure for x > 0.07. The dielectric data shows that the amount of Bi(Zn2/3Nb1/3)O3 added in the (K1/2Na1/2)NbO3 decreases the ferroelectric - paraelectric transition temperature progressively. Furthermore, optimum piezoelectric and ferroelectric properties were observed at the composition, x = 0.01: effective piezoelectric coefficients (d33) = 498 pm/V, remanent polarization (Pr) = 23.3 μC/cm², coercive field (Ec) = 14 kV/cm, maximum strain (Smax) = 0.3% and Curie temperature (TC) = 380°C. The results of this study show that KNN with a small amount of Bi(Zn2/3Nb1/3)O3 (x = 0.01) can be one of lead-free piezoelectric ceramic candidate.