Enhanced Ferroelectric and Piezoelectric Properties of Textured K_0.45Na_0.55NbO₃ Ceramics Prepared by Screen-printing Technique

Grain oriented K0.45Na0.55NbO3 (KNN) lead-free piezoceramics with sintering aid K4CuNb8O23 (KCN) were fabricated by screen-printing technique, using plate-like NaNbO3 as templates. The plate-like NaNbO3 template particles were synthesized from bismuth layer-structured Bi2.5Na3.5Nb5O18 precursors by the topochemical micro-crystal conversion method. The textured KNN ceramics showed brick-wall-like grains which aligned parallel to the screen-printing direction. The screen-printed KNN ceramics possessed both a high grain orientation (Lotgering factor f=95%) and a relative high density (92% of theoretical density). The orientation degree and electrical properties of textured (K0.45Na0.55)NbO3 ceramics exhibited anisotropic feature in the parallel (sp parallel to) and perpendicular (sp perpendicular to) plane. Compared with the random oriented ceramics with same composition, the dielectric constant e piezoelectric constant d(33), and electromechanical coupling coefficient k(p) were increased by about 75%, 44% and 42% in sp parallel to plane, respectively, and about 35%, 30% and 35% in sp perpendicular to plane, respectively. Screen-printing is a simple and effective method for the fabrication of grain oriented lead-free piezoelectric ceramics.