The market for lead-based piezoceramics, mainly (Pb1-x ZrxTiO3, PZT) - based materials, is higher than $100 billion per year. Due to lead-toxicity, the demand for lead-free piezoceramics is increasing. Potassium Sodium Niobate solid solutions, namely K0.5Na0.5NbO3, KNN, is currently one of the most promising materials for electromechanical applications. However, monophasic conventionally sintered KNN is hard to obtain, due to alkali evaporation during sintering (T\u3e 1100 ºC, t \u3e 2h). Within this context, there is an increasing interest in sustainable sintering techniques, as FLASH, to decrease both sintering time and temperature, avoiding alkali vaporization. However, FLASH applied to bulk ceramics, frequently produces inhomogeneous specimens.
Figure 1 – Variation of length with temperature of FLASH sintered KNN, after a 2 h isothermal step. SEM micrograph showing the uniformly dense microstructure.
In this work, we propose an experimental approach that allows the production of homogeneous, highly dense, KNN. In this method, the use of FLASH sintering contributed to reduce KNN sintering temperature for more than 200 ºC and the cycle time in ~3h. Uniform densification was achieved by using an isothermal step before the application of the electric field. Scanning Electron Microscopy (SEM) and Specific Surface Area (SSA) measurements were performed to characterize the pre-FLASH sintering microstructure.
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