Structural and dielectric properties of La and Nb co-substituted Bi0.5(Na0.84K0.16)0.5TiO3-SrTiO3 ceramics

In this article La and Nb co-substitution effect on the crystal structure, microstructure, ferroelectric and dielectric properties of 0.96[{Bi
0.5
(Na
0.84
K
0.16
)
0.5
}
1−x
La
x
(Ti
1−y
Nb
y
)O
3
]-0.04SrTiO
3
(BNKLTN-ST, where (x=y) = 0.00 − 0.020) ceramics has been investigated. The ceramics with x,y ≤ 0.010 have pure perovskite structure, while a secondary phase appears in the sample with x=y = 0.020. X-ray diffraction patterns revealed that La and Nb co-doping resulted in a transition from coexistent rhombohedral and tetragonal phases to pseudocubic symmetry. The co-doping of La and Nb slightly increased the average grain size. The maximum permittivity temperature (T
m
) increased with increasing La and Nb contents, but the values of depolarization temperature (T
d
) as well as maximum dielectric constant (ε
m
) decrease gradually. La and Nb addition interrupted the polarization and reveals that the ferroelectric (FE) order of unmodified BNKT-ST ceramics lead to a declination of remnant polarization along with coercive field. The results shows that La and Nb co-doping into BNKT-ST ceramics induces a phase transition from relaxor FE to ergodic relaxor phase with a substantial deterioration of the long-range FE order.