**2.1. NaNbO3 synthesis**

NaNbO3 powders were obtained by microwave hydrothermal synthesis which was carried out beginning with NaOH (p. a. Quemis) and Nb2O5 (Alfa Aesar, 99%). In the reaction to form NaNbO3, the NaOH acts as a mineralizing agent and sodium source. The reaction was carried out in a Teflon vessel model XP-1500 (CEM Corp.), in a MARS-5 (CEM Corp.) microwave oven. The precursor suspensions were prepared with 0.696 g of Nb2O5 added to 30 mL of 8 mol.L–1 NaOH water solution. The suspension was then transferred into Teflon vessels which were placed inside a microwave furnace. The synthesis was carried out at 180°C with different conditions as given in Table 1. The obtained powders were thoroughly washed with distilled water by centrifugation and finally dried at room temperature.


**Table 1.** Microwave hydrothermal synthesis conditions for obtaining NaNbO3 particles.
