Effect of the level of addition of Nb2O5/Co2O3 and Ba(Nb2/3Co1/3)O3 on the structure, microstructure, and dielectric properties of BaTiO3

In this work attempt is made to study the effects of the level of the addition of two dopant systems, that is, Nb₂O₅/Co₂O₃ and Ba(Nb_2/3Co_1/3)O₃ on the structure, microstructure, and dielectric properties of BaTiO₃(BT) prepared by ceramic route. For the BT samples doped with 2 and 3 at % Nb₂O₅/Co₂O₃ a broad maxima for _r–T variations was observed. Higher levels of addition, that is, 6, 8, and 10 at % Nb₂O₅/Co₂O₃, however, caused a drastic reduction in the magnitude of _r and vanishing of maxima peaks observed. The reduction in the magnitudes of the _r for these samples is related to the observed reduction of the tetragonality of doped BT samples as well as the existence of some non-ferroelectric extra phase, evidenced by our XRD analysis. The existence of this extra phase is also believed to be mainly responsible for the observed increase of the dielectric loss. For the BT samples doped with Ba(Nb_2/3Co_1/3)O₃ perovskite solid solution, the _r maxima peak could only be detected for the samples doped with 2 at %. In the case of the samples doped with 4, 6, 8, and 10 at % perovskite solid solution, however, a very uniform distribution of _r–T was observed. The increase of the level of dopant for these series of samples was also seen to give rise in the reduction of the magnitude of _r. However, this reduction was not as strong as the cases observed for the samples doped with 8 and 10 at % Nb₂O₅/Co₂O₃. XRD patterns obtained for these series of samples also revealed the reduction of tetragonality of the BT samples when doped with Ba(Nb_2/3Co_1/3)O₃. Further, microstructural studies carried out by scanning electron microscopy (SEM) on both series of samples revealed a contrasting picture. While a uniform grain size distribution was observed for the whole series of the samples doped with Ba(Nb_2/3Co_1/3)O₃, a non-uniform size distribution of grain sizes was observed in the case of samples doped with Nb₂O₅/Co₂O₃. This is thought to be due to the possible formation and non-uniform distribution of a liquid phase due to the formation of Ti-rich region in the shell region of Nb₂O₅/Co₂O₃-doped samples. The existence of such liquid phase, in case of Nb₂O₅/Co₂O₃-doped samples, would have the consequence of an increased rate of diffusion of Nb/Co into the BT cores leaving narrow compositional fluctuations for the shell regions.