Barium titanate

Barium titanate is an oxide of barium and titanium with the chemical formula BaTiO₃. It is a ferroelectric ceramic material, with a photorefractive effect and piezoelectric properties. It has five phases as a solid, listing from high temperature to low temperature: hexagonal, cubic, tetragonal, orthorhombic, and rhombohedral crystal structure. All of the structures exhibit the ferroelectric effect except cubic.

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Appearance

It has the appearance of a white powder or transparent crystals. It is insoluble in water and soluble in concentrated sulfuric acid. Its risk and safety phrases are R20/22, S28A, S37, and S45.

Manufacture

Barium titanate can be manufactured by sintering of barium carbonate and titanium dioxide, optionally with other materials for doping.

High purity [barium nitrate] powder is reported to be a key component of new capacitor energy storage systems being developed by EEStor for use in electric vehicles.^[1]

Barium titanate is often mixed with strontium titanate.

Uses

Barium titanate is used as a dielectric material for ceramic capacitors, and as a piezoelectric material for microphones and other transducers. As a piezoelectric material, it was largely replaced by lead zirconate titanate, also known as PZT.

Polycrystalline barium titanate displays positive temperature coefficient, making it an useful material for thermistors and self-regulating electric heating systems.

Fully-dense nanocrystalline barium titanate has 40% higher permittivity than the same material prepared in classic ways.^[2]

Barium titanate crystals find use in nonlinear optics. The material has high beam-coupling gain, and can be operated at visible and near-infrared wavelengths. It has the highest reflectivity of the materials used for self-pumped phase conjugation (SPPC) applications. It can be used for continuous-wave four-wave mixing with milliwatt-range optical power. For photorefractive applications, barium titanate can be doped by various other elements, eg. cerium.^[3]

The addition of inclusions of barium titanate to tin has been shown to create a bulk material with a higher viscoelastic stiffness than that of diamonds. Barium titanate goes through two phase transitions that change the crystal shape and volume. This leads to composites where the barium titanates have a negative bulk modulus (Young's modulus), meaning that when a force acts on the inclusions, there is displacement in the opposite direction, further stiffening the composite.^[4]

Thin films of barium titanate display electrooptic modulation to frequencies over 40 GHz.^[5]

The pyroelectric and ferroelectric properties of barium titanate are used in some types of uncooled sensors for thermal cameras.

See also

• Strontium titanate
• Lead zirconate titanate

References

1. ^ http://www.zenncars.com/investor/releases/Certification_EEStor_01_16_2007.pdf
2. ^ http://research.ucdavis.edu/NCD.cfm?ncdid=658[1]
3. ^ http://www.redoptronics.com/Ce:BaTiO3-crystal.html Ce:BaTiO₃
4. ^ http://www.sciencemag.org/cgi/content/abstract/315/5812/620 [2]
5. ^ http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-24-5962 [3]