Sodium bismuth titanate or bismuth sodium titanium oxide (NBT or BNT) is a solid inorganic compound of sodium, bismuth, titanium and oxygen with the chemical formula of Na<sub>0.5</sub>Bi<sub>0.5</sub>TiO<sub>3</sub> or Bi<sub>0.5</sub>Na<sub>0.5</sub>TiO<sub>3</sub>. This compound adopts the perovskite structure.
Na<sub>0.5</sub>Bi<sub>0.5</sub>TiO<sub>3</sub> 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 Na<sub>2</sub>CO<sub>3</sub>, Bi<sub>2</sub>O<sub>3</sub> and TiO<sub>2</sub> at temperatures around 850 ðC.
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<sub>0.5</sub>Bi<sub>0.5</sub>TiO<sub>3</sub> 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 (space group Cc) was proposed. On heating, Na<sub>0.5</sub>Bi<sub>0.5</sub>TiO<sub>3</sub> transforms at 533 ñ 5 K to a tetragonal structure (space group P4bm) and above 793 ñ 5 K to cubic structure (space group Pmm).
Na<sub>0.5</sub>Bi<sub>0.5</sub>TiO<sub>3</sub> is a relaxor ferroelectric. Its optical band gap was reported to be in the 3.0âÂÂ3.5 eV.
Various solid solutions with tetragonal ferroelectric perovskites including BaTiO<sub>3</sub>, Bi<sub>0.5</sub>K<sub>0.5</sub>TiO<sub>3</sub> have been developed to obtain morphotropic phase boundaries to enhance the piezoelectric properties of Na<sub>0.5</sub>Bi<sub>0.5</sub>TiO<sub>3</sub>. 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.