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Mixed Anion Compounds
Mixed-anion compounds, heteroanionic materials or mixed-anion materials are chemical compounds containing cations and more than one kind of anion. The compounds contain a single phase, rather than just a mixture. Use in materials science By having more than one anion, many more compounds can be made, and properties tuned to desirable values. In terms of optics, properties include phosphorescence, photocatalysis, laser damage threshold, refractive index, birefringence, absorption (electromagnetic radiation), absorption particularly in the ultraviolet or near infrared, non-linearity. Mechanical properties can include ability to grow a large crystal, ability to form a thin layer, strength, or brittleness. Thermal properties can include melting point, thermal stability, phase transition temperatures, thermal expansion coefficient. For electrical properties, electric conductivity, band gap, superconducting transition temperature piezoelectricity, pyroelectricity, ferromagnetism, dielec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemical Compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element is therefore not a compound. A compound can be transformed into a different substance by a chemical reaction, which may involve interactions with other substances. In this process, bonds between atoms may be broken or new bonds formed or both. There are four major types of compounds, distinguished by how the constituent atoms are bonded together. Molecular compounds are held together by covalent bonds; ionic compounds are held together by ionic bonds; intermetallic compounds are held together by metallic bonds; coordination complexes are held together by coordinate covalent bonds. Non-stoichiometric compounds form a disputed marginal case. A chemical formula specifies the number of atoms of each element in a compound molecule, usin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pyroelectricity
Pyroelectricity (from Greek: ''pyr'' (πυρ), "fire" and electricity) is a property of certain crystals which are naturally electrically polarized and as a result contain large electric fields. Pyroelectricity can be described as the ability of certain materials to generate a temporary voltage when they are heated or cooled. The change in temperature modifies the positions of the atoms slightly within the crystal structure, so that the polarization of the material changes. This polarization change gives rise to a voltage across the crystal. If the temperature stays constant at its new value, the pyroelectric voltage gradually disappears due to leakage current. The leakage can be due to electrons moving through the crystal, ions moving through the air, or current leaking through a voltmeter attached across the crystal. Explanation Pyroelectric charge in minerals develops on the opposite faces of asymmetric crystals. The direction in which the propagation of the charge tends is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxyarsenide
Oxyarsenides or arsenide oxides are chemical compounds formally containing the group AsO, with one arsenic and one oxygen atom. The arsenic and oxygen are not bound together as in arsenates or arsenites, instead they make a separate presence bound to the cations (metals), and could be considered as a mixed arsenide-oxide compound. So a compound with OmAsn requires cations to balance a negative charge of 2m+3n. The cations will have charges of +2 or +3. The trications are often rare earth elements or actinides. They are in the category of oxypnictide compounds. Some of these compounds are superconductors, but may require doping with fluoride or oxygen deficiency. Yet others undergo colossal magnetoresistance Colossal magnetoresistance (CMR) is a property of some materials, mostly manganese-based perovskite oxides, that enables them to dramatically change their electrical resistance in the presence of a magnetic field. The magnetoresistance of conventio ... with a lowered electrical ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxyphosphide
Oxyphosphides are chemical compounds formally containing the group PO, with one phosphorus and one oxygen atom. The phosphorus and oxygen are not bound together as in phosphates or phosphine oxides, instead they are bound separately to the cations (metals), and could be considered as a mixed phosphide-oxide compound. So a compound with OmPn requires cations to balance a negative charge of 2m+3n. The cations will have charges of +2 or +3. The trications are often rare earth elements or actinides. They are in the category of oxy-pnictide compounds. Many compounds are layered, containing two metals with the formula XZPO, with an XP layer alternating with a ZO layer. Examples Examples include *Ca4P2O greenish gold, has space group ''I''4''mmm'' Z=2 and unit cell parameters a = 4.492, c = 15.087. *Uranium–Copper Oxyphosphide UCuPO semimetallic antiferromagnetic tetragonal ZrCuSiAs-type a =3:7958 c=8:2456 V=118.80 Z=2 MW=348.55 density=9.743 *Thorium–Copper Oxyphosphide ThCuPO sem ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxynitride
The oxynitrides are a group of inorganic compounds containing oxygen and nitrogen not bound to each other, instead combined with other non-metallic or metallic elements. Some of these are oxosalts with oxygen replaced by nitrogen. Some of these compounds do not have a fixed oxygen to nitrogen ratio, but instead form ceramics with a range of compositions. They are in the class of mixed anion compounds. Many can be formed by heating an oxide or carbonate with ammonia. The hydrogen can assist by reducing some of the oxygen. With higher temperatures and pressures nitrogen can be heated with a mixed oxide to yield a product. Other nitrogen rich compounds that can be heated with oxygen containing material are urea and melamine. For example urea heated with ammonium dihydrogen phosphate Ammonium dihydrogen phosphate (ADP), also known as monoammonium phosphate (MAP) is a chemical compound with the chemical formula (NH4)(H2PO4). ADP is a major ingredient of agricultural fertilizers and d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxypnictide
In chemistry, oxypnictides are a class of materials composed of oxygen, a pnictogen (group-V, especially phosphorus and arsenic) and one or more other elements. Although this group of compounds has been recognized since 1995, interest in these compounds increased dramatically after the publication of the superconducting properties of LaOFeP and LaOFeAs which were discovered in 2006 and 2008. In these experiments the oxide was partly replaced by fluoride. These and related compounds (e.g. the 122 iron arsenides) form a new group of iron-based superconductors known as iron pnictides or ferropnictides since the oxygen is not essential but the iron seems to be. Oxypnictides have been patented as magnetic semiconductors in early 2006. The different subclasses of oxypnictides are oxynitrides, oxyphosphides, oxyarsenides, oxyantimonides, and oxybismuthides. Structure Many of the oxypnictides show a layered structure. For example, LaFePO with layers of La3+O2− and Fe2+P3−. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coordination Number
In chemistry, crystallography, and materials science, the coordination number, also called ligancy, of a central atom in a molecule or crystal is the number of atoms, molecules or ions bonded to it. The ion/molecule/atom surrounding the central ion/molecule/atom is called a ligand. This number is determined somewhat differently for molecules than for crystals. For molecules and polyatomic ions the coordination number of an atom is determined by simply counting the other atoms to which it is bonded (by either single or multiple bonds). For example, [Cr(NH3)2Cl2Br2]− has Cr3+ as its central cation, which has a coordination number of 6 and is described as ''hexacoordinate''. The common coordination numbers are 4, 6 and 8. Molecules, polyatomic ions and coordination complexes In chemistry, coordination number, defined originally in 1893 by Alfred Werner, is the total number of neighbors of a central atom in a molecule or ion. The concept is most commonly applied to coordination ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solvothermal Synthesis
Solvothermal synthesis is a method of producing chemical compounds, in which a solvent containing reagents is put under high pressure and temperature in an autoclave. Many substances dissolve better in the same solvent in such conditions than at standard conditions, enabling reactions that would not otherwise occur and leading to new compounds or polymorphs. Solvothermal synthesis is very similar to the hydrothermal route; both are typically conducted in a stainless steel autoclave. The only difference being that the precursor solution is usually non-aqueous. Solvothermal synthesis has been used prepare MOFs, titanium dioxide, and graphene Graphene () is a carbon allotrope consisting of a Single-layer materials, single layer of atoms arranged in a hexagonal lattice, honeycomb planar nanostructure. The name "graphene" is derived from "graphite" and the suffix -ene, indicating ..., carbon spheres, chalcogenides and other materials. Solvents Besides water (hydrothermal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Soft Chemical
Soft chemistry (also known as chimie douce) is a type of chemistry that uses reactions at ambient temperature in open reaction vessels with reactions similar to those occurring in biological systems. Aims The aim of the soft chemistry is to synthesize materials, drawing capacity of living beings - more or less basic - such as diatoms capable of producing glass from silicates dissolved. It is a new branch of materials science that differs from conventional solid-state chemistry and its application to the intense energy to explore the chemical inventiveness of the living world. This specialty emerged in the 1980s around the label of "chimie douce", which was first published by the French chemist, Jacques Livage in ''Le Monde'', 26 October 1977.J. Livage, "Vers une chimie écologique. Quand l’air et l’eau remplacent le pétrole", Le Monde (1977) October 26th French hits, the term ''soft chemistry'' is employed as such in the early twenty-first century in scientific publication ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrogen Sulfide
Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist Carl Wilhelm Scheele is credited with having discovered the chemical composition of purified hydrogen sulfide in 1777. Hydrogen sulfide is toxic to humans and most other animals by inhibiting cellular respiration in a manner similar to hydrogen cyanide. When it is inhaled or its salts are ingested in high amounts, damage to organs occurs rapidly with symptoms ranging from breathing difficulties to convulsions and death. Despite this, the human body produces small amounts of this sulfide and its mineral salts, and uses it as a signalling molecule. Hydrogen sulfide is often produced from the microbial breakdown of organic matter in the absence of oxygen, such as in swamps and sewers; this process is commonly known as anaerobic digestio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
