Sodium bismuth titanate explained

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_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.

Structure

See main article: Perovskite (structure). 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.^[1] In 2010, based on the high-resolution single-crystal X-ray diffraction data, a monoclinic structure (space group Cc) was proposed. On heating, Na_0.5Bi_0.5TiO₃ transforms at 533 ± 5 K to a tetragonal structure (space group P4bm) and above 793 ± 5 K to cubic structure (space group Pmm).^[2]

Physical properties

Na_0.5Bi_0.5TiO₃ is a relaxor ferroelectric. Its optical band gap was reported to be in the 3.0–3.5 eV.^[3]

Applications

See main article: Piezoelectricity. Various solid solutions with tetragonal ferroelectric perovskites including BaTiO₃,^[4] Bi_0.5K_0.5TiO₃^[5] 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.^[6]

Further reading

• Lead-Free Piezoelectrics, Ed. Shashank Priya and Sahn Nahm,(2012), Springer-Verlag, New York. .

Notes and References

1. Smolenskii, G. . Isupov, V. . Agranovskaya, A. . Krainik, N. . New ferroelectrics of complex composition. . Sov. Phys. Solid State . 1961. 2 . 2651–2654.
2. Zvirgzds, J.A. . Kapostin, P.P. . Zvirgzde, J.V. . Kruzina, T.V. . X-ray study of phase transitions in ferroelectric Na_0.5Bi_0.5TiO₃. Ferroelectrics . 1982 . 40. 1 . 75–77. 10.1080/00150198208210600 . 1982Fer....40...75Z .
3. Bousquet, M. . Duclere, J.R. . Orhan, E. . Boulle, A. . Bachelet, C. . Champeaux, C . Optical properties of an epitaxial Na_0.5Bi_0.5TiO₃ thin film grown by laser ablation: Experimental approach and density functional theory calculations. 107. 104107–104107–13. J. Appl. Phys.. 2010. 10 . 10.1063/1.3400095. 2010JAP...107j4107B .
4. Takenaka, T. . Maruyama, K.-I. . Sakata, K. . (Bi_1/2Na_1/2)TiO₃-BaTiO₃ system for lead-free piezoelectric ceramics.. 30. 2236–2239. Jpn. J. Appl. Phys. Part 1. 1991. 9S . 10.1143/JJAP.30.2236. 1991JaJAP..30.2236T . 124093028 .
5. Sasaki, A.; Chiba, T.; Mamiya, Y.; Otsuki, E. Dielectric and piezoelectric properties of (Bi_0.5Na_0.5)TiO₃-(Bi_0.5K_0.5)TiO₃ systems. Jpn. J. Appl. Phys. Part 1 1999, 38, 5564–5567.
6. Reichmann, K. . Feteira, A., Li M. . Bismuth Sodium Titanate Based Materials for Piezoelectric Actuators. 8. 8467–8495. Materials. 2015. 12 . 10.3390/ma8125469. 28793724 . 5458809. 2015Mate....8.8467R . free .