Barium titanate
Identifiers
CAS number	12047-27-7 Y
SMILES	[Ba+2].[Ba+2].[O-][Ti]([O-])([O-])[O-]
InChI	1/2Ba.4O.Ti/q2*+2;4*-1;/r2Ba.O4Ti/c;;1-5(2,3)4/q2*+2;-4
InChI key	JRPBQTZRNDNNOP-NXYSCRTKAD
ChemSpider ID	10605734
Properties
Molecular formula	BaTiO3
Molar mass	233.192 g/mol
Appearance	white crystals
Density	6.02 g/cm3, solid
Melting point	1625 °C
Solubility in water	insoluble
Solubility	slightly soluble in dilute mineral acids; dissolves in concentrated sulfuric acid and hydrofluoric acid
Structure
Crystal structure	Tetragonal, tP5
Space group	P4mm, No. 99
Hazards
R-phrases	R20/22
S-phrases	S28A, S37, and S45
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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. Barioperovskite is a very rare natural analogue of BaTiO₃, found as microinclusions in benitoite.

[edit] Properties

Structure of BaTiO₃. The red spheres are oxygens, blue are Ti⁴⁺ cations, and the green ones are Ba²⁺.

Barium titanate has the appearance of a white powder or transparent crystals. It is insoluble in water and soluble in concentrated sulfuric acid.

[edit] Manufacture

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

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

Barium titanate is often mixed with strontium titanate.

[edit] Uses

Barium titanate is used as a dielectric material for ceramic capacitors, and as a piezoelectric material for microphones and other transducers. The Curie point of barium titanate is 120 °C. 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 a 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, e.g. iron.^[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.

[edit] See also

• Strontium titanate
• Lead zirconate titanate

[edit] References

[edit] External links

• Nanoparticle Compatibility: New Nanocomposite Processing Technique Creates More Powerful Capacitors
• EEStor's "instant-charge" capacitor batteries