Influence of excess sodium addition on the structural characteristics and electrical conductivity of Na0.5Bi0.5TiO3

The current study investigates the influence of adding excess Na on the structure and conductivity of Na0.5Bi0.5TiO3. Polycrystalline bulk samples were prepared via conventional solid-state reaction method. XRD confirmed the presence of rhombohedral perovskite as a primary phase in all the samples. SEM revealed the existence of secondary phases which were found to increase considerably with the higher addition of excess Na. Chemical analysis via EDXS indicates Na deficiency in the sintered sample of stoichiometric Na0.5Bi0.5TiO3, while the average Na/Bi molar ratio found to be more than unity in all the Na-excess compositions. Impedance spectroscopy studies showed at least 3 orders of magnitude conductivity difference between the Na-excess and pure Na0.5Bi0.5TiO3 samples. The bulk conductivity was found to increase with the addition of excess Na, which was attributed to the increase in oxygen vacancy. Although partial substitution of Na for A-site Bi appears to be a promising strategy for the conductivity enhancement, these compositions show significant segregation of secondary phases on excess Na addition.