Ferroelectric NaNbO₃ Ceramics Fabricated by Spark Plasma Sintering

High-density ceramic samples of NaNbO₃ (NN) have been successfully fabricated by spark plasma sintering (SPS), which is a process that uses microscopic electrical discharge between particles under pressure. The obtained NN ceramic shows a hysteresis loop characteristic of ferroelectrics. The coercive electric field, E_c, and remanent polarization, P_r, are determined to be 12 kV/cm and 0.42 µC/cm², respectively, for an unpoled sample and 16 kV/cm and 27 µC/cm², respectively, for a poled sample. The NN ceramic also shows piezoelectricity with a planar electromechanical coupling factor, K_p, of about 20%. The ferroelectricity and piezoelectricity in the NN ceramic are stable at high temperatures. The piezoelectric characteristic does not change after annealing at 300°C but it disappears after annealing at 350°C.