Structure and dielectric properties in Mg/Nb co-substituted bismuth sodium titanate

A systematic study of pseudo-isovalent B site co-substitution of Ti4+ by Mg2+ and Nb5+ in bismuth sodium titanate is presented. A complete solid solution in the Bi0.5Na0.5Ti1−x(Mg1/3Nb2/3)xO3 system is formed. With increasing level of substitution, dielectric anomalies associated with depoling and maximum permittivity temperatures (Td and Tm, respectively) are suppressed and shift to lower temperatures. Variable temperature X-ray powder diffraction on the x = 0.2 composition reveals a non-linear thermal expansion at temperatures below Tm. B-site co-substitution by Mg and Nb has the effect of interrupting the long-range ferroelectric ordering in the system, resulting in lower saturation and remnant polarizations. A maximum energy storage density of 4.14 J cm−3 with a recoverable energy density of 2.35 J cm−3 was obtained for the x = 0.1 composition, while the x = 0.5 composition appears to have the best balance between energy storage and energy efficiency.