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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. Additional recommended knowledge
AppearanceIt 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. ManufactureBarium 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. UsesBarium 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 alsoReferences
Categories: Titanates | Barium compounds |
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Barium_titanate". A list of authors is available in Wikipedia. |