|
Bismuth Titanate
Bismuth titanate or bismuth titanium oxide is a solid inorganic compound of bismuth, titanium and oxygen with the chemical formula of Bi12TiO20, Bi 4Ti3O12 or Bi2Ti2O7. Synthesis Bismuth titanate ceramics can be produced by heating a mixture of bismuth and titanium oxides. Bi12TiO20 forms at 730–850 °C, and melts when the temperature is raised above 875 °C, decomposing in the melt to Bi4Ti3O12 and Bi2O3. Millimeter-sized single crystals of Bi12TiO20 can be grown by the Czochralski process, from the molten phase at 880–900 °C. Properties and applications Bismuth titanates exhibit electrooptical effect and photorefractive effect, that is, a reversible change in the refractive index under applied electric field or illumination, respectively. Consequently, they have potential applications in reversible recording media for real-time holography Holography is a technique that enables a wavefront to be recorded and later re-constructed. Holography is best kn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pearson Symbol
The Pearson symbol, or Pearson notation, is used in crystallography as a means of describing a crystal structure, and was originated by W. B. Pearson. The symbol is made up of two letters followed by a number. For example: * Diamond structure, ''cF''8 * Rutile structure, ''tP''6 The two (italicised) letters specify the Bravais lattice. The lower-case letter specifies the crystal family, and the upper-case letter the centering type. The number at the end of the Pearson symbol gives the number of the atoms in the conventional unit cell.Nomenclature of Inorganic Chemistry IUPAC Recommendations 2005 IR-3.4.4, pp. 49–51; IR-11.5, pp. 241–242. |
Refractive Index
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or refracted, when entering a material. This is described by Snell's law of refraction, , where ''θ''1 and ''θ''2 are the angle of incidence and angle of refraction, respectively, of a ray crossing the interface between two media with refractive indices ''n''1 and ''n''2. The refractive indices also determine the amount of light that is reflected when reaching the interface, as well as the critical angle for total internal reflection, their intensity ( Fresnel's equations) and Brewster's angle. The refractive index can be seen as the factor by which the speed and the wavelength of the radiation are reduced with respect to their vacuum values: the speed of light in a medium is , and similarly the wavelength in that medium is , where '' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Piezoelectric Materials
Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress. The word ''piezoelectricity'' means electricity resulting from pressure and latent heat. It is derived from the Greek word ; ''piezein'', which means to squeeze or press, and ''ēlektron'', which means amber, an ancient source of electric charge. The piezoelectric effect results from the linear electromechanical interaction between the mechanical and electrical states in crystalline materials with no inversion symmetry. The piezoelectric effect is a reversible process: materials exhibiting the piezoelectric effect also exhibit the reverse piezoelectric effect, the internal generation of a mechanical strain resulting from an applied electrical field. For example, lead zirconate titanate crystals will generate measurable piezoelectricity when thei ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ceramic Materials
A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain, and brick. The earliest ceramics made by humans were pottery objects (''pots,'' ''vessels or vases'') or figurines made from clay, either by itself or mixed with other materials like silica, hardened and sintered in fire. Later, ceramics were glazed and fired to create smooth, colored surfaces, decreasing porosity through the use of glassy, amorphous ceramic coatings on top of the crystalline ceramic substrates. Ceramics now include domestic, industrial and building products, as well as a wide range of materials developed for use in advanced ceramic engineering, such as in semiconductors. The word "''ceramic''" comes from the Greek word (), "of pottery" or "for pottery", from (), "potter's clay, tile, pottery". The earliest known m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bismuth Compounds
Bismuth compounds are compounds containing the element bismuth (Bi). Bismuth forms trivalent and pentavalent compounds, the trivalent ones being more common. Many of its chemical properties are similar to those of arsenic and antimony, although they are less toxic than derivatives of those lighter elements. Oxides and sulfides At elevated temperatures, the vapors of the metal combine rapidly with oxygen, forming the yellow trioxide, . Wiberg, p. 768. Greenwood, p. 553. When molten, at temperatures above 710 °C, this oxide corrodes any metal oxide and even platinum. Krüger, p. 185 On reaction with a base, it forms two series of oxyanions: , which is polymeric and forms linear chains, and . The anion in is a cubic octameric anion, , whereas the anion in is tetrameric. The dark red bismuth(V) oxide, , is unstable, liberating gas upon heating. The compound NaBiO3 is a strong oxidising agent. Greenwood, p. 578. Bismuth sulfide, , occurs naturally in bismuth ores. It i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sillénite
Sillénite or sillenite is a mineral with the chemical formula Bi12SiO20. It is named after the Swedish chemist Lars Gunnar Sillén, who mostly studied bismuth-oxygen compounds. It is found in Australia, Europe, China, Japan, Mexico and Mozambique, typically in association with bismutite. Sillenites refer to a class of bismuth compounds with a structure similar to Bi12SiO20, whose parent structure is γ-Bi2O3, a meta-stable form of bismuth oxide. The cubic crystal sillenite structure is shared by several synthetic materials including bismuth titanate and bismuth germanate Bismuth germanium oxide or bismuth germanate is an inorganic chemical compound of bismuth, germanium and oxygen. Most commonly the term refers to the compound with chemical formula (BGO), with the cubic evlitine crystal structure, used as a sci .... These compounds have been extensively investigated for their non-linear optical properties. Additional stoichiometries, and modified structures, are also found ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bismuth Germanate
Bismuth germanium oxide or bismuth germanate is an inorganic chemical compound of bismuth, germanium and oxygen. Most commonly the term refers to the compound with chemical formula (BGO), with the cubic evlitine crystal structure, used as a scintillator. (The term may also refer to a different compound with formula Bi12GeO20, an electro-optical material with sillenite structure, and .) Bi4Ge3O12 Bi4Ge3O12 has a cubic crystal structure (''a'' = 1.0513 nm, ''z'' = 4, Pearson symbol ''cI76'', space group I3d No. 220) and a density of 7.12 g/cm3. When irradiated by X-rays or gamma rays it emits photons of wavelengths between 375 and 650 nm, with peak at 480 nm it produces about 8500 photons per megaelectronvolt of the high energy radiation absorbed. It has good radiation hardness (parameters remaining stable up to 5.104 Gy), high scintillation efficiency, good energy resolution between 5 and 20 MeV, is mechanically strong, and is not hygroscopic. Its melting point ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Holography
Holography is a technique that enables a wavefront to be recorded and later re-constructed. Holography is best known as a method of generating real three-dimensional images, but it also has a wide range of other applications. In principle, it is possible to make a hologram for any type of wave. A hologram is made by superimposing a second wavefront (normally called the reference beam) on the wavefront of interest, thereby generating an interference pattern which is recorded on a physical medium. When only the second wavefront illuminates the interference pattern, it is diffracted to recreate the original wavefront. Holograms can also be computer-generated by modelling the two wavefronts and adding them together digitally. The resulting digital image is then printed onto a suitable mask or film and illuminated by a suitable source to reconstruct the wavefront of interest. Overview and history The Hungarian- British physicist Dennis Gabor (in Hungarian: ''Gábor Déne ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photorefractive Effect
The photorefractive effect is a nonlinear optical effect seen in certain crystals and other materials that respond to light by altering their refractive index. The effect can be used to store temporary, erasable holograms and is useful for holographic data storage. It can also be used to create a phase-conjugate mirror or an optical spatial soliton. Mechanism The photorefractive effect occurs in several stages: #A photorefractive material is illuminated by coherent beams of light. (In holography, these would be the signal and reference beams). Interference between the beams results in a pattern of dark and light fringes throughout the crystal. #In regions where a bright fringe is present, electrons can absorb the light and be photoexcited from an impurity level into the conduction band of the material, leaving an electron hole (a net positive charge). Impurity levels have an energy intermediate between the energies of the valence band and conduction band of the material. #Onc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bismuth Silicon Oxide
Bismuth silicon oxide is a solid inorganic compound of bismuth, silicon and oxygen. Its most common chemical formula is Bi12SiO20, though other compositions are also known. It occurs naturally as the mineral sillénite and can be produced synthetically, by heating a mixture of bismuth and silicon oxides. Centimeter-sized single crystals of Bi12SiO20 can be grown by the Czochralski process from the molten phase. They exhibit piezoelectric, electro-optic, elasto-optic, photorefractive and photoconductive properties, and therefore have potential applications in spatial light modulators, acoustic delay lines and hologram recording equipment. Bi12SiO20 can be obtained as a whitish powder with band gap of approximately 3.2 eV starting from bismuth subcarbonate and silica in presence of ethyleneglycol. 29Si solid-state NMR is used to proof that the Si(IV) cations are sharing oxygen atoms with the Bi(III) cations. The 29Si chemical shift (δ) in Bi12SiO20 is −78.1 ppm. Unlike the bismut ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrooptical Effect
Electrophoresis, from Ancient Greek ἤλεκτρον (ḗlektron, "amber") and φόρησις (phórēsis, "the act of bearing"), is the motion of dispersed particles relative to a fluid under the influence of a spatially uniform electric field. Electrophoresis of positively charged particles (cations) is sometimes called cataphoresis, while electrophoresis of negatively charged particles (anions) is sometimes called anaphoresis. The electrokinetic phenomenon of electrophoresis was observed for the first time in 1807 by Russian professors Peter Ivanovich Strakhov and Ferdinand Frederic Reuss at Moscow University, who noticed that the application of a constant electric field caused clay particles dispersed in water to migrate. It is ultimately caused by the presence of a charged interface between the particle surface and the surrounding fluid. It is the basis for analytical techniques used in chemistry for separating molecules by size, charge, or binding affinity. Electropho ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
_oxide_2.jpg "Click for more on -> Bismuth Compounds")
