| Piezoelectric thick films (with thickness in the range of 10 to 100μm) which have the merits of both the bulk material and thin film are of great interest due to the drive for miniaturisation, high power/sensitivity, multi-function, and system integration with the electric circuits. The purpose of the present work is to fabricate and evaluate sodium-potassium bismuth titanate (NKBT) lead free piezoelectric thick film on electroded alumina substrate by the screen printing.Double layers Pt bottom electrodes for NKBT thick films have been screen printed on alumina substrates. As the first layer sintered at 600℃, the double Pt layers with sequential heat treatments at 1200℃exhibt improved densification and surface coverage. The double Pt layers with the minimum average roughness of 0.6μm and the smallest sheet resistivity of 0.044Ω/(?) have been produced. NKBT lead free piezoelectric ceramic powders were prepared by using solid phase synthesis, The organic vehicles consisted 5wt.% ethyl cellulose as binder, 2wt.% 2-(2-n-Butoxyethoxy) ethyl as dispersing agent, 1wt.% dibutyl phthalate and DBP as a plasticizer, and 92wt.%α-terpineol as solvent (α-terpineol). The screen printing pastes were produced by mixing the ceramic powders and the organic vehicles together with the mol ratio of 3:1. The viscosity of the prepared paste was adjusted by viscosimeter in the range 20-80 Pa.s for shear rate 18-1 s.NKBT thick films with A and B site substitution have been produced by La2O3 and MnO2 doping, respectively. In order to reduce the annealing temperature, the NKBT thick films doped with 0.6Bi2O3-0.4Li2O as sintering aids were manufactured, and their microstructural, dielectric and piezoelectric properties were investigated. The results show that MnO2 doping increases the grain size, grain uniformity, density, and content of tetragonal phase of the NKBT thick film. The resulting 40μm thick films have maximum relative permittivity of 735, (at 10 kHz), longitudinal piezoelectric coefficient d33 of 88 pC/N, remanent polarization of 28.5μC/cm2, and pyroelectric coefficient of 3.8×10-4 C/m2℃(25℃), minimum dissipation of 2.2%, and coercive field of 54 kV/cm. The La2O3 doped NKBT thick films have smaller grain, higher conten of tetragonal phase and antiferroelectric phase, and higher optimal annealing temperature than undoped NKBT thick films. The dielectric constant of the NKBT thick film increases with increasing La2O3 content, and the maximum dielectric,εmax of the NKBT thick film decreases with increasing La2O3 content. The NKBT thick films have the minimum leakage current density of 1.56×10-9A/cm2 (100kV/cm applied bias ) and maximum longitudinal piezoelectric coefficient d33 of 87 pC/N when doped 1.0 mol% La2O3. The NKBT thick films doped 0.5 mol% La2O3 have the higher remanent polarization of 19.3μC/cm2. When 3 wt.% 0.6Bi2O3-0.4Li2O were added, the NKBT thick film can be sintered at 1000℃, the apparent density of 95.54% and remanent polarization of 19.6μC/cm2.NKBT thick films have been produced using a combination of screen printing and subsequent infiltration of corresponding composite sol. The densification mechanism and the effects of residual stress on electric characteristics of NKBT thick films have been investigated. The results show that the differences in dielectric and piezoelectric properties between the thick film and corresponding ceramic result from internal bias and low dielectric layer in thick film.Their structure, dielectric, ferroelectric and piezoelectric properties were investigated with variation in the number of composite sol infiltrations and the nanopowder loading in composite sol. The NKBT thick films which were infiltrated by the composite precursor solution with higher solids loading (1.5 g/ml) exhibited superior dielectric properties compared with the NKBT thick film infiltrated with pure sol. The best performance of the NKBT thick films with six infiltrations were dielectric constant of 768, dielectric loss of 2.3% at 10 kHz, remnant polarization of 21.3μC/cm2, and coercive field of 59 kV/cm respectively. When 3wt.% sintering aids added, the NKBT thick films with twelve infiltrations have the maximum longitudinal piezoelectric coefficient d33 of 102 pC/N. The effects of the residual stress on the electrical properties of NKBT thick films were investigated. The resulting 80μm thick films sintered at 1100℃have the higher tensile stress of 136MPa, and the residual stress decreases with increasing thickness of the thick films.The dielectric and piezoelectric aging were attributed to the decrease of the domain wall contribution to the permittivity which corresponds to a gradual change of the 90? domain wall with time, and the ferroelectric fatigue was resulted from pinning of domain wall due to increase of defect concentrations. Moreover, the increase of the test temperature enhanced the pinning effect which related to oxygen vacancy concentration and resulted in quicher aging and fatigue. The aging and fatigue characteristics of NKBT thick films were improved by adding excessive Bi2O3 due to decreases of A site vacancies.
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