Impact of multiple phases on ferroelectric and piezoelectric performances of BNKT–BZT ceramic

Lead-free (1−x)Bi_0.5(Na_0.8K_0.2)_0.5TiO₃–xBaZr_0.1Ti_0.9O₃ (with x = 0.0, 0.02, 0.025, 0.030, 0.035, 0.040) were prepared by conventional solid state reaction method. The effect of different amount of barium zirconate titanate (BZT) on structural, microstructural, ferroelectric and piezoelectric properties was examined experimentally through X-ray diffraction, scanning electron microscope and field-induced polarization and strain measurement. The coexistence of rhombohedral/tetragonal phase has been observed in pure BNKT. Now, with the addition of BZT contents in pure BNKT, the tetragonal phase has been observed to be dominant over rhombohedral, but still, mixed phase coexists in entire composition range. The temperature dependent dielectric constant and room temperature ferroelectric hysteresis show a strong dependence on their crystallographic phases. Piezoelectric properties reveal that the BNKT–0.025BZT ceramic has a large unipolar strain of 0.21% (S_max/E_max = 430 pm/V) at room temperature under an external field of 5 kV/mm. Addition of BZT reduces the remnant polarization and hysteresis loss, suggesting ferroelectric ceramics for future energy storage applications.