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Corundum (structure)
Corundum is the name for a structure prototype in inorganic solids, derived from the namesake polymorph of aluminum oxide (α-Al2O3). Other compounds, especially among the inorganic solids, exist in corundum structure, either in ambient or other conditions. Corundum structures are associated with metal-insulator transition, ferroelectricity, polar magnetism, and magnetoelectric effects. Structure The corundum structure has the space group . It typically exists in binary compounds of the type A2B3, where A is metallic and B is nonmetallic, including sesquioxides (A2O3), sesquisulfides (A2S3), etc. When A is nonmetallic and B is metallic, the structure becomes the antiphase of corundum, called the anticorundum structure type, with examples including β-Ca3N2 and borates. Ternary and multinary compounds can also exists in the corundum structure. The corundum-like structure with the composition A2BB'O6 is called double corundum. A list of examples are tabulated below. See al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymorphism (materials Science)
In materials science, polymorphism describes the existence of a solid material in more than one form or crystal structure. Polymorphism is a form of isomerism. Any crystalline material can exhibit the phenomenon. Allotropy refers to polymorphism for chemical elements. Polymorphism is of practical relevance to pharmaceuticals, agrochemicals, pigments, dyestuffs, foods, and explosives. According to IUPAC, a polymorphic transition is "A reversible transition of a solid crystalline phase at a certain temperature and pressure (the inversion point) to another phase of the same chemical composition with a different crystal structure." According to McCrone, polymorphs are "different in crystal structure but identical in the liquid or vapor states." Materials with two polymorphs are called dimorphic, with three polymorphs, trimorphic, etc. Examples Many compounds exhibit polymorphism. It has been claimed that "every compound has different polymorphic forms, and that, in general, the n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gallium(III) Oxide
Gallium(III) oxide is an inorganic compound and ultra-wide bandgap semiconductor with the formula Ga2 O3. It is actively studied for applications in power electronics, phosphors, and gas sensing. The compound has several polymorphs, of which the monoclinic β-phase is the most stable. The β-phase’s bandgap of 4.7–4.9 eV and large-area, native substrates make it a promising competitor to GaN and SiC-based power electronics applications and solar-blind UV photodetectors. Ga2O3 exhibits reduced thermal conductivity and electron mobility by an order of magnitude compared to GaN and SiC, but is predicted to be significantly more cost-effective due to being the only wide-bandgap material capable of being grown from melt. β-Ga2O3 is thought to be radiation hard which makes it promising for military and space applications. Preparation Gallium trioxide is precipitated in hydrated form upon neutralization of acidic or basic solution of gallium salt. Also, it is formed on heat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ilmenite
Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printing inks, fabrics, plastics, paper, sunscreen, food and cosmetics. Structure and properties Ilmenite is a heavy (specific gravity 4.7), moderately hard (Mohs hardness 5.6 to 6), opaque black mineral with a submetallic luster. It is almost always massive, with thick tabular crystals being quite rare. It shows no discernible cleavage, breaking instead with a conchoidal to uneven fracture. Ilmenite crystallizes in the trigonal system with space group ''R''. The ilmenite crystal structure consists of an ordered derivative of the corundum structure; in corundum all cations are identical but in ilmenite Fe2+ and Ti4+ ions occupy alternating layers perpendicular to the trigonal c axis. Pure ilmenite is paramagnetic (showing only very weak attrac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Corundum
Corundum is a crystalline form of aluminium oxide () typically containing traces of iron, titanium, vanadium and chromium. It is a rock-forming mineral. It is a naturally transparent material, but can have different colors depending on the presence of transition metal impurities in its crystalline structure. Corundum has two primary gem varieties: ruby and sapphire. Rubies are red due to the presence of chromium, and sapphires exhibit a range of colors depending on what transition metal is present. A rare type of sapphire, padparadscha sapphire, is pink-orange. The name "corundum" is derived from the Tamil- Dravidian word ''kurundam'' (ruby-sapphire) (appearing in Sanskrit as ''kuruvinda''). Because of corundum's hardness (pure corundum is defined to have 9.0 on the Mohs scale), it can scratch almost all other minerals. It is commonly used as an abrasive on sandpaper and on large tools used in machining metals, plastics, and wood. Emery, a variety of corundum with no value a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vanadate
In chemistry, a vanadate is an anionic coordination complex of vanadium. Often vanadate refers to oxoanions of vanadium, most of which exist in its highest oxidation state of +5. The complexes and are referred to as hexacyanovanadate(III) and nonachlorodivanadate(III), respectively. A simple vanadate ion is the tetrahedral orthovanadate anion, (which is also called vanadate(V)), which is present in e.g. sodium orthovanadate and in solutions of in strong base ( pH > 13). Conventionally this ion is represented with a single double bond, however this is a resonance form as the ion is a regular tetrahedron with four equivalent oxygen atoms. Additionally a range of polyoxovanadate ions exist which include discrete ions and "infinite" polymeric ions. There are also vanadates, such as rhodium vanadate, , which has a statistical rutile structure where the and ions randomly occupy the positions in the rutile lattice, that do not contain a lattice of cations and balancing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromite (compound)
In chemistry the term chromite has been used in two contexts. Under IUPAC naming conventions, ''chromate(III)'' is preferred to ''chromite''. #For compounds containing an oxyanion of chromium in oxidation state 3 #For other compounds of chromium(III) as a means of distinguishing a chemical species such as hexacyanochromite(III). r(CN)6sup>3− from an analogous compound in which chromium is a different oxidation state. The mineral chromite is an iron chromium oxide with empirical formula FeCr2O4. Structurally, it belongs to the spinel group. Magnesium can substitute for iron in variable amounts as it forms a solid solution with magnesiochromite (MgCr2O4);. Zincochromite is another example. The crystal structure of the acid, HCrO2 has been determined by neutron diffraction Neutron diffraction or elastic neutron scattering is the application of neutron scattering to the determination of the atomic and/or magnetic structure of a material. A sample to be examined is placed in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Titanate
In chemistry, titanate usually refers to inorganic compounds composed of titanium oxides. Together with niobate, titanate salts form the Perovskite group. In some cases, the term is used more generally for any titanium-containing anion, e.g. iCl6sup>2− and i(CO)6sup>2−. This article focuses on the oxides. Many kinds of titanium oxides are known, and some are commercially important. Typically these materials are white, diamagnetic, high-melting, and insoluble in water. They are often prepared at high temperatures, e.g. using tube furnaces, from titanium dioxide. In virtually all cases, titanium achieves octahedral coordination geometry.. Orthotitanates Orthotitanates have the formula M2TiO4, where M is divalent. An example of such a material is magnesium titanate (Mg2TiO4), which adopts the spinel structure. Li2TiO3 is not considered an orthotitanate since it adopts the rock-salt structure and does not feature an identifiable titanium anion. Orthotitanates almost never feat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Borate
A borate is any of several boron oxyanions, negative ions consisting of boron and oxygen, such as orthoborate , metaborate , or tetraborate ; or any salt with such anions, such as sodium metaborate, and disodium tetraborate . The name also refers to certain functional groups in molecules consisting of boron and oxygen, and esters with such groups, such as triethyl orthoborate . Natural occurrence Borate ions occur, alone or with other anions, in many borate and borosilicate minerals such as borax, boracite, ulexite (boronatrocalcite) and colemanite. Borates also occur in seawater, where they make an important contribution to the absorption of low frequency sound in seawater. Borates also occur in plants, including almost all fruits. Anions The main borate anions are: * tetrahydroxyborate , found in sodium tetrahydroxyborate . * orthoborate , found in trisodium orthoborate * perborate , as in sodium perborate * metaborate or , found in sodium metaborate * diborate , f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sulfide
Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds large families of inorganic and organic compounds, e.g. lead sulfide and dimethyl sulfide. Hydrogen sulfide (H2S) and bisulfide (SH−) are the conjugate acids of sulfide. Chemical properties The sulfide ion, S2−, does not exist in aqueous alkaline solutions of Na2S. Instead sulfide converts to hydrosulfide: :S2− + H2O → SH− + OH− Upon treatment with an acid, sulfide salts convert to hydrogen sulfide: :S2− + H+ → SH− :SH− + H+ → H2S Oxidation of sulfide is a complicated process. Depending on the conditions, the oxidation can produce elemental sulfur, polysulfides, polythionates, sulfite, or sulfate. Metal sulfides react with halogens, forming sulfur and metal salts. :8 MgS + 8 I2 → S8 + 8 M ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nitride
In chemistry, a nitride is an inorganic compound of nitrogen. The "nitride" anion, N3- ion, is very elusive but compounds of nitride are numerous, although rarely naturally occuring. Some nitrides have a find applications, such as wear-resistant coatings (e.g., titanium nitride, TiN), hard ceramic materials (e.g., silicon nitride, Si3N4), and semiconductors (e.g., gallium nitride, GaN). The development of GaN-based light emitting diodes was recognized by the 2014 Nobel Prize in Physics. Metal nitrido complexes are also common. Synthesis of inorganic metal nitrides is challenging because nitrogen gas (N2) is not very reactive at low temperatures, but it becomes more reactive at higher temperatures. Therefore, a balance must be achieved between the low reactivity of nitrogen gas at low temperatures and the entropy driven formation of N2 at high temperatures. However, synthetic methods for nitrides are growing more sophisticated and the materials are of increasing technological re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thallium(III) Oxide
Thallium(III) oxide, also known as thallic oxide, is a chemical compound of thallium and oxygen. It occurs in nature as the rare mineral avicennite. Its structure is related to that of Mn2O3 which has a bixbyite like structure. Tl2O3 is metallic with high conductivity and is a degenerate n-type semiconductor which may have potential use in solar cells. A method of producing Tl2O3 by MOCVD is known. Any practical use of thallium(III) oxide will always have to take account of thallium's poisonous nature. Contact with moisture and acids may form poisonous thallium compounds. Production It is produced by the reaction of thallium with oxygen or hydrogen peroxide in an alkaline thallium(I) solution. Alternatively, it can be created by the oxidation of thallium(I) nitrate by chlorine in an aqueous potassium hydroxide Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash. Along with sodium hydroxide (NaOH), KOH is a prototypical ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rhodium(III) Oxide
Rhodium(III) oxide (or Rhodium sesquioxide) is the inorganic compound with the formula Rh2 O3. It is a gray solid that is insoluble in ordinary solvents. Structure Rh2O3 has been found in two major forms. The hexagonal form adopts the corundum structure. It transforms into an orthorhombic structure when heated above 750 °C. Production Rhodium oxide can be produced via several routes: * Treating RhCl3 with oxygen at high temperatures. * Rh metal powder is fused with potassium hydrogen sulfate. Adding sodium hydroxide results in hydrated rhodium oxide, which upon heating converts to Rh2O3. * Rhodium oxide thin films can be produced by exposing Rh layer to oxygen plasma. * Nanoparticles can be produced by the hydrothermal synthesis. Physical properties Rhodium oxide films behave as a fast two-color electrochromic system: Reversible yellow ↔ dark green or yellow ↔ brown-purple color changes are obtained in KOH solutions by applying voltage ~1 V. Rhodium oxide fil ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
