Sodium bismuth titanate

Sodium bismuth titanate or bismuth sodium titanium oxide is a solid inorganic compound of sodium, bismuth, titanium and oxygen with the chemical formula of Na_0.5Bi_0.5TiO₃ or Bi_0.5Na_0.5TiO₃. This compound adopts the perovskite structure.

Synthesis

Na_0.5Bi_0.5TiO₃ is not a naturally occurring mineral and several synthesis routes to obtain the compound have been developed. It can be easily prepared by solid state reaction between Na₂CO₃, Bi₂O₃ and TiO₂ at temperatures around 850 °C.

The exact room-temperature crystal structure of sodium bismuth titanate has been a matter of debate for several years. Early studies in the 1960s using X-ray diffraction suggested Na_0.5Bi_0.5TiO₃ to adopt either a pseudo-cubic or a rhombohedral crystal structure. In 2010, based on the high-resolution single-crystal X-ray diffraction data, a monoclinic structure was proposed. On heating, Na_0.5Bi_0.5TiO₃ transforms at 533 ± 5 K to a tetragonal structure and above 793 ± 5 K to cubic structure.

Na_0.5Bi_0.5TiO₃ is a relaxor ferroelectric. Its optical band gap was reported to be in the 3.0–3.5 eV.

Various solid solutions with tetragonal ferroelectric perovskites including BaTiO₃, Bi_0.5K_0.5TiO₃ have been developed to obtain morphotropic phase boundaries to enhance the piezoelectric properties of Na_0.5Bi_0.5TiO₃. The extraordinarily large strain generated by a field-induced phase transition in sodium bismuth titanate-based solid solutions prompted researchers to investigate its potential as an alternative to lead zirconate titanate for actuator applications.