Increasing demand for functional ceramic products with complex shapes and high dimensional accuracy resulted in the development of different additive manufacturing methods. Digital light processing (DLP) was proven as one of the reliable and cost-efficient techniques for ceramic materials. DLP allows versatile geometries and ensures the high surface quality of final products. Main research based on DLP has been concentrated on structural ceramics and lead-based piezoceramics. However, environmental considerations encourage efforts to extend additive manufacturing on lead-free piezoceramics.
In this work, the feasibility of producing piezoceramics with (100-x)Na_1/2Bi_1/2TiO₃-xBaTiO₃ (NBT-BT) powder by the DLP method was investigated. NBT-6BT powder was prepared by solid-state synthesis from carbonates and oxides. The median particle size d₅₀ of the calcined powder was 0.9 μm. The synthesized ceramic powder was subsequently stabilized and mixed with 1,6-Hexanediol diacrylate, photoinitiator and dispersing agents. The challenges associated with the relatively high bulk density of the material were tackled by varying solid loads of the suspension from 10 to 40 vol.%, modifications of the dispersing agents, and mixing parameters. A viscosity function over the shear rate showed a pseudoplastic tendency for all investigated solid loads. Viscosity values at a share rate of 120 s^-1 for ceramic slurries with 10-40 vol.% increased from 0.1 to 16.3 Pa·s. The light-activated polymerization was performed using LEDs with wavelengths from 370 nm to 500 nm. In order to evaluate the curing depth after photopolymerization, suspensions with lead-free piezoceramic powders were illuminated with different ultraviolet light intensities and exposure durations. Debinding and sintering processes were optimized by thermogravimetric and differential thermal analyses. Microscopical investigations were performed for the powders and the obtained sintered ceramics. The microstructure of the sintered sample with 40 vol.% solid load exhibited a 96 % relative density and an average grain size of 0.61 μm. Electromechanical and dielectric properties, such as piezoelectric coefficient d₃₃, temperature dependant dielectric permittivity, and polarization loops were measured. The findings of this research prove the feasibility of fabricating NBT-BT piezoceramics by the DLP method with properties comparable to conventionally produced samples.