Effect of varying Bi content on the temperature-dependent mechanical, dielectric, and structural properties of nominal Na1/2Bi1/2TiO3

Na1/2Bi1/2TiO3 (NBT) with varying Bi content has gained significant interest as a potential new material for solid-oxide fuel cells and oxygen separation membranes because of its excellent oxygen-ion conductivity. In this work, the effect of varying Bi content in NBT ceramics of compositions Na1/2BixTiO2.25+1.5x, where x = 0.485–0.510, on the temperature-dependent mechanical and dielectric properties and the crystal structure has been investigated, as these applications expose the components to high thermal and mechanical fields. The effects of Bi variation on phase compositions and structural transitions were systematically investigated by scanning electron microscopy-energy dispersive x-ray analyses and neutron diffraction at room temperature, in situ high-temperature x-ray diffraction, dielectric permittivity, and mechanical measurements. In-depth analysis of the temperature-dependent data shows that the Bi content of the samples does not alter the average crystal structure of the NBT; however, the temperature-dependent behavior of the latter depend on variations in Bi content and the associated oxygen vacancy concentration. This change in phase transition temperature displays a good correlation with the temperature-dependent ferroelastic response and with the Bi content.