Effect of lanthanum substitution on structural, dielectric and piezoelectric properties of (Na0.41K0.09Bi0.5)TiO3: A lead-free piezoelectric material

The effect of lanthanum doping (0.5-5 mol%) on structural, dielectric and piezoelectric response of (Na0.41K0.09Bi0.5)TiO3 ceramic has been investigated. The x-ray studies reveal that there is no structural transformation with incorporation of lanthanum. However, a gradual lowering of tetragonal-to-rhombohedral transitions and depolarization temperature was observed in the dielectric response. For lower lanthanum contents (0-2 mol%) the piezoelectric coefficients i.e d(33) (150 pC/N) and k(p) (0.31) are nearly same. A significant decrease of d 33 and k(p) was observed for higher lanthanum doping with emergence of pinched P-E hysteresis loop. These results are explained on the basis of disruption of long-range ferroelectric ordering in (Na0.41K0.09Bi0.5)TiO3 with lanthanum doping as well as with emergence of anti-ferroelectric ordering. A structural phase diagram has also been derived for lanthanum doped (Na0.41K0.09Bi0.5)TiO3 using dielectric measurements.