Sodium bismuth titanate

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

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 Pm3m).^[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

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]

References

1. Smolenskii, G.; Isupov, V.; Agranovskaya, A.; Krainik, N. (1961). "New ferroelectrics of complex composition.". Sov. Phys. Solid State 2: 2651–2654.
2. Zvirgzds, J.A.; Kapostin, P.P.; Zvirgzde, J.V.; Kruzina, T.V. (1982). "X-ray study of phase transitions in ferroelectric Na_0.5Bi_0.5TiO₃". Ferroelectrics 40: 75–77.
3. Bousquet, M.; Duclere, J.R.; Orhan, E.; Boulle, A.; Bachelet, C.; Champeaux, C (2010). "Optical properties of an epitaxial Na_0.5Bi_0.5TiO₃ thin film grown by laser ablation: Experimental approach and density functional theory calculations". J. Appl. Phys. 107: 104107. doi:10.1063/1.3400095.
4. Takenaka, T.; Maruyama, K.-I.; Sakata, K. (1991). "(Bi_1/2Na_1/2)TiO₃-BaTiO₃ system for lead-free piezoelectric ceramics.". Jpn. J. Appl. Phys. Part 1. 30: 2236–2239. doi:10.1143/JJAP.30.2236.
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. (2015). "Bismuth Sodium Titanate Based Materials for Piezoelectric Actuators". Materials 8: 8467–8495. doi:10.3390/ma8125469.

Further reading

Lead-Free Piezoelectrics, Ed. Shashank Priya and Sahn Nahm,(2012), Springer-Verlag, New York. DOI:10.1007/978-1-4419-9598-8.