The spinels are a group of minerals that share a particular arrangement of atoms within the unit cell. The special behaviours of a random distribution of ions in linivo4 and noncollinear magnetic structures in licuvo4 are studied based on density functional theory. Spinel and antispinel are two classifications of inorganic crystals. Although the charges of a and b in the prototypical. The spinels with ideal structure crystallizes in cubic system fcc, forming octahedral crystals belonging to space group fd3m. Formation and evolution of spinel in aluminum killed. Kushwaha 21 has calculated the zonecentre phonons for the inverse spinel compounds efin 2s 4 and niin 2s 4 using rigid ion model.
Normal spinel and inverse spinel chemistry stack exchange. Spinel ferrites mfe 2 o 4 have a cubic crystal symmetry with eight formula units in the unit cell. Madelung energy is higher for the normal spinel if u 0. A hard, variously colored mineral with composition mgal2o4, having usually octahedral crystals, occurring in igneous and metamorphosed carbonate rocks, and valued as a gem.
Contain tetrahedral and octahedral holes based on type of metal atom occupying them, they are classified into two types i. An inverse spinel is an alternative arrangement where the divalent ions swap with half of the trivalent ions so that the mii now occupy octahedral sites i. Their general molecular formula is miimiiio4 or sulfur instead of oxygen in it. The second type of spinels is the so called inverse spinel. Therefore, in order to characterize the spinel structure fully, a further parameter is needed describing the degree of inversion. The spinels are any of a class of minerals of general formulation ab 2 x 4 which crystallise in the cubic isometric crystal system, with the x anions typically chalcogens, like oxygen and sulfur arranged in a cubic closepacked lattice and the cations a and b occupying some or all of the octahedral and tetrahedral sites in the lattice. An inverse spinel nife 2 o 4 spinel is the name given to the mineral mgal 2 o 4. Formation and evolution of spinel in aluminum killed calcium treated linepipe steels by obinna m. Colorless, pale gray, pale graygreen, pale green, pale blue, pale pink pleochroism. Cobalt intensifies the blue color in spinel, considerably enhancing its beauty. Although spinel has been used in jewelry since ancient times, this gemstone has only recently received the attention it deserves. Distinguishing heated spinels from unheated natural. In catio3 cubic the oxygen anions and calcium cations form a cubic close packing whereas titanium cations occupy 14 of the octahedral holes. Spinel is the name given to the mineral mgal 2 o 4.
Spinel comes in a variety of colors, but the most commercially important are red and pink. Nife 2 o 4 is a wellknown inverse spinel with ni 2. Spinel is generally highly sought after by gem connoisseurs, and wellformed spinel crystals are in high demand among collectors. It has a common structural arrangement shared by many oxides of the transition metals with formula ab 2 o 4. Spinels article about spinels by the free dictionary. The anion fractional coordinate u in the spinel structure was shown to depend strongly on the cation inversion parameter. For linivo4, the random distribution of lini ions is ascribed to the cubic groundstate structure of the compound. The logarithm of the equilibrium constant k for the site exchange reaction in spinels as a function of the degree of inversion, x. Special electronic structures of inverse spinels limvo 4. In a very recent theoretical study based on density functional theory, li et al. Before the rise of modern gemology in the late 19 th and early 20 th centuries, spinel was often identified as corundum, as they are often found in the same mines. Detailed investigations on inverse spinels have recently started. Blue cobalt spinel are at least 10100x more expensive per carat than grayishblue colored spinel. There are two cation sublatticestetrahedral a and octahedral b.
Role of point defects in spinel mg chalcogenide conductors. Spinels a normal spinel structure is assumed if both the divalent and the trivalent metals are non transition metals since no cfse is involved. Spinel and chromite are normal spinels, magnetite is an inverse spinel. Mauve or lilaccolored spinels are also attractive, and some blue spinel colors can be. The structure of a magnetite crystal is called the inverse spinel structure. In the normal pattern the oxygens red form a cubic close packed abcabc or face centred array and the mgii aiigreen and aliii biiisilver sit in tetrahedral 18 occupied and octahedral 12. It therefore implies the presence of two kinds of cations in bsites in inverse spinels leads to an additional contribution to the madelung energy. Its name comes from the latin word spinella, which means spine in reference to its pointed crystals. Simple tricks iit jam csir net gate adichemistry duration. Normal spinels, inverse spinels and mixed spinels youtube. Introduction cobaltspinels are considered one of the most precious spinel and are rarely colored blue with or without grey to black tones. Nevertheless, these minerals are chemically distinct. Spinel structure definition of spinel structure by the. The crystal structure for magnetite is shown in figure 1, 2 below.
In reality, most spinels are somewhere between the two end states. The spinels forms one of major family of crystalline oxides. Crystals are usually octahedrons yielding triangular, square, or diamondshaped cross sections in thin section. Spinels are systems of solid solutions, with extensively developed isomorphism of the a and b cations. A totally disordered configuration is obtained for i 0. It has a distorted octahedral structure resulting from elongation along the z axis. Sudarat saeseaw, wuyi wang, kenneth scarratt, john l. Cubic close packed system, cubic sites occupied by oxide ligand, which are weak field ligands. Although the spinels are important minerals themselves, their real geological significance is that olivine. When li and ni ions are distributed alternately and homogeneously, an antiferromagnetic structure is found to be the. Any of a group of minerals that are oxides of magnesium, iron, zinc, manganese, or. If it is the other way around, an inverse spinel is to be expected.
Their name comes from the mineral mgal 2 o 4, which has a homologous crystalline structure. World of magnificent spinels provenance and identification burma vietnam inclusions in spinel cornflowerblue spinel over 10ct from vietnam online release pages 12, 269282. Investigation on lattice constants of mgal spinels jing shouyong chengdu fine optical engineering centre, chengdu 610041, peoples republic of china email. Lattice dynamical calculations for inverse spinel compounds. Cobaltspinel over 5ct can be 10,000 to 30,000 us dollar per carat depending. Adaba a thesis presented to graduate faculty of the missouri university of science and technology in partial fulfillment of the requirements for the degree master of science in metallurgical engineering 2015 approved by. In this case niii is octahedral and half of the feiii are tetrahedral.
With increasing temperature there will be a tendency for both normal and inverse spinels to disorder towards the random, maximum entropy, cation arrangement, at x 23. The cations located within the oxygen framework are octahedrally sixfold and tetrahedrally fourfold coordinated with oxygen. Olivine, spinel, garnet olivine major constituent mineral of the earths upper mantle, found in peridotite rock. Synthesis, characterization and dc conduction mechanism in. Comparative compressibility and structural behavior of. It has the formula mgal 2 o 4 in the cubic crystal system. Spinel definition is a hard crystalline mineral consisting of an oxide of magnesium and aluminum that varies from colorless to ruby red to black and is used as a gem. The spinel series contains the mineral spinel, also called ruby spinel q. Spinel spinels generally refer to metal oxides having general formula ab2x4 the spinel that is most popularly known is mgal2o4 3. Spinels that trend towards x 23 from the low x side of this divide.
The aluminum spinels are harder, more transparent, and less dense than the others. A set of cation radii optimized to best fit spinel lattice parameters is presented. They are classified according to the predominant b cation as. Pdf electronic structures of normal and inverse spinel. Pdf mixed spinel structure in nanocrystalline nife2o4. In uence of inversion on mg mobility and electrochemistry. Where aii a divalent cation like mg, cr, mn, fe, co, ni, cu, zn. Throughout the article the kr ogervink notation is employed to identify the type of point defects in the mga 2z 4 spinels, including chalcogenide vacancies e. Fe 3 o 4 fe iiifeiifeiiio 4 cofe 2 o 4 fe iiicoiifeiiio 4 nife 2 o 4 fe iiiniiifeiiio 4 the number of octahedral sites occupied may be ordered or random. Spinel is a common phase in all samples except 11919 and occurs as euhedral to subhedral grains in the sample matrix, as partially resorbed grains with garnet coronas figure. Distinguishing heated spinels from unheated natural spinels and from synthetic spinels. Electronic structures of normal and inverse spinel ferrites from first principles. Magnetism in spinel and garnet structures 151 for lnig.
Complexes that share this structure include a number of. Chapter 2 crystal structure and magnetism in spinel ferrite. There is a tendency of formation of inverse spinel structure in some cases not all the cases which contain transition metal ions. Like in the building process of the spinels, we suppose that the feo4 covalent groups build the space, and that between them the atoms of the other metals act as a cement, build the space. Calcium is cuboctahedrally coordinated by 12 oxide ions whereas. The spinelgroup minerals have type xy 2 o 4 and contain oxygen atoms in approximate cubic closest packing. Simple method for calculation of spinel and inverse spinel structure. Lattice parameters and stability of the spinel compounds. Examples for spinel and inverse spinel structures 1 mgal 2 o 4 is a normal spinel since both the divalent and trivalent ions are non transition metal ions. Temperature dependence of the cation distribution in. The general formula for this kind of structure is abo3 where a and b atoms are cations catio3 is an ideal example for the perovskite structure. Synthesis and characterization of spinel oxide compounds.
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