spinel

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spinel,

magnesium aluminum oxide, MgAl2O4, a mineral crystallizing in the isometric system, usually as octahedrons. It occurs as an accessory mineral in basic igneous rocks, in aluminum-rich metamorphic rocks, and in contact-metamorphosed limestones. Common spinel usually ranges in color from dark green to brown or black, but transparent red, blue, and green varieties are found and are used as gemstones; Myanmar and Sri Lanka are the principal producing countries. Much gem-quality spinel is now produced synthetically.
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spinel

[spə′nel]
(mineralogy)
MgAl2O4 A colorless, purplish-red, greenish, yellow, or black mineral, usually forming octahedral crystals, and characterized by great hardness; used as a gemstone.
A group of minerals of general formula AB2O4, where A is magnesium, ferrous iron, zinc, or manganese, or a combination of them, and B is aluminum, ferric iron, or chromium.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Mixed spinel structure, when cations [Me.sup.2+] and [Fe.sup.3+] occupy both A and B positions; structural formula of this ferrite is [Me.sub.1-x.sup.2+][Fe.sub.x.sup.3+] [[Me.sub.x.sup.2+][Fe.sub.2-x.sup.3+]] [O.sub.4.sup.2-], where x is the degree of inversion [8].
While magnetization measurements on the same system could be explained by Neel's model as far as the series remained inverse spinel, they deviated significantly when they began to have normal spinel structure [10].
Some of manganite nanocatalyst compounds with spinel structure were synthesized in the research through self-combusting sol-gel method, and their physicochemical properties were identified through various techniques.
The diffraction peaks of all the samples can be completely indexed in the cubic spinel structure (JCPDS#49-0207).
Cobalt ferrite has a partially inverse spinel structure in which both sites, i.e.
It is clear that the specimens with x = 0.5 and 0.7 exhibit single-phase spinel structure. Obviously, increasing the content of Zn is favorable for the synthesis of pure Mg-Zn ferrites.
The [gamma]-[Fe.sub.2][O.sub.3] with cubic spinel structure has similar structure with a Fe([Fe.sub.5/3][[??].sub.1/3])[O.sub.4] unit, in which [??] represents a cation vacancy, in the hexagonal Ba[Fe.sub.12][O.sub.19] structure, and so is easily transformed to the hexaferrite by reaction with BaC[O.sub.3] and BaO(Wei Zhong, 1997).
The whole [Co.sub.3][O.sub.4] has a spinel structure with the space group of Fd3m(227), and CoO has a rock salt structure with the space group of Fm3m(225).
[Co.sub.3][O.sub.4] with a typical spinel structure and characteristics of simple synthesis, low cost and environment-friendly, has many functional applications, including sensors [9], catalysts [10], and lithium ion batteries [11].
The transition layer consisted of grain boundary oxides of chromia and chromite and fine oxide grains of a spinel structure precipitated inside laths [5].
X-ray diffraction (XRD) patterns (Figure 1) of Cu substituted NiZn ferrites can be well indexed to JCPDS card number 01-071-3850, thereby establishing the formation of single phase cubic spinel structure. The patterns showed the absence of other impurity phases unlike the appearance of second phase of CuO or Cu[Fe.sub.2][O.sub.4] for ferrite composition of x [greater than or equal to] 0.3 prepared by coprecipitation method [11].
TEM/SAED experiments (Figure 3) confirmed the results of PXRD: the matrix-free NPs (Figures 3(a) and 3(b)) correspond to the Co[Fe.sub.2][O.sub.4] spinel structure (Crystallography Open Database [41], record ID = 5910063).