Rheology and physical properties of Bi0.5(Na0.82K0.18)0.5TiO3 piezoelectric thick films by aqueous gel-tape casting process

Piezoelectric Bi_0.5(Na_0.82K_0.18)_0.5TiO₃ thick films were prepared by aqueous gel-tape casting. Bi_0.5(Na_0.82K_0.18)_0.5TiO₃ nano-powder with perovskite structure prepared by sol–gel process was obtained. The average particle size was 200 nm. A stable Bi_0.5(Na_0.82K_0.18)_0.5TiO₃ suspension with 46 vol% solid loading and <1 Pa s viscosity was prepared when 0.8 wt% of ammonium polyacrylate was added with the pH value controlled in the range 7–9. The plasticizer glycerol had a positive effect on the fluidity of the suspensions. The tensile strength and strain to failure of the green tape were 0.42 MPa and 0.04 mm/mm when the addition of glycerol was 50 wt% of the premix solvent. The resulting about 100 μm thick films had relative permittivity of 910, dielectric loss of 4.9% at 10 kHz, remanent polarization of 24 μC/cm², coercive field of 56 kV/cm, and longitudinal effective piezoelectric coefficient d₃₃eff of 102 pC/N. The good performance illustrated that gel-tape casting was the effective way to prepare Bi_0.5(Na_0.82K_0.18)_0.5TiO₃ thick film.