Fluoritová struktura: Porovnání verzí
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'''Fluoritová struktura''' je druh struktury sloučenin odpovídajících vzorci MX<sub>2</sub>.<ref>{{Citace monografie |
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{{Pracuje se}} |
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| příjmení = Greenwood |
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| titul = Chemistry of the Elements |
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| url = https://books.google.cz/books?vid=ISBN9780080379418 |
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| vydání = 2 |
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| vydavatel = Elsevier Science & Technology Books |
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| rok vydání = 1997 |
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| počet stran = |
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| isbn = 978-0-08-037941-8 |
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| jazyk = en |
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}}</ref> Ionty X obsazují osm tetraedrických míst a ionty M vytvářejí [[krychlová soustava|plošně centrovanou krychlovou strukturu]]. Pojmenována je podle [[fluorit]]u (CaF<sub>2</sub>). |
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Řada sloučenin se vzorcem M<sub>2</sub>X má '''antifluoritovou strukturu''', kdy jsou polohy [[anion]]tů a [[kation]]tů oproti fluoritu prohozené, takovou látkou je například [[silicid hořečnatý]], Mg<sub>2</sub>Si, v němž je každý [[silicidy|silicidový]] anion obklopen osmi [[hořčík|hořečnatými]] kationty a každý hořečnatý kation sousedí se čtyřmi silicidovými anionty.<ref name=Costel>{{Citace monografie | autor1 = Costel Rizescu | autor2 = Mihaela Rizescu | titul = Structure of Crystalline Solids, Imperfections and Defects in Crystals | url = https://shutterwaves.com/product/structure-of-crystalline-solids/ | vydavatel = Shutter Waves | rok vydání = 2018 | isbn = 978-1-947641-17-4}}</ref> |
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<!-- '''fluorite structure''' refers to a common motif for compounds with the formula MX<sub>2</sub>.<ref>{{Holleman&Wiberg}}</ref><ref>{{Greenwood&Earnshaw2nd}}</ref> The X ions occupy the eight tetrahedral [[interstitial site]]s whereas M ions occupy the regular sites of a [[Cubic crystal system|face-centered cubic]] (FCC) structure. Many compounds, notably the common mineral [[fluorite]] (CaF<sub>2</sub>), adopt this structure. |
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Many compounds with formula M<sub>2</sub>X have an '''antifluorite structure'''. In these the locations of the anions and cations are reversed relative to fluorite (an [[anti-structure]]); the anions occupy the FCC regular sites whereas the cations occupy the tetrahedral interstitial sites. For example, [[magnesium silicide]], Mg<sub>2</sub>Si, has a lattice parameter of 6.338 Å with magnesium cations occupying the tetrahedral interstitial sites, in which each [[silicide]] anion is surrounded by eight magnesium cations and each magnesium cation is surrounded by four silicide anions in a tetrahedral fashion.<ref name="Costel">{{cite book|url=https://shutterwaves.com/product/structure-of-crystalline-solids/|title=Structure of Crystalline Solids, Imperfections and Defects in Crystals|last1=Rizescu|first1=Costel|last2=Rizescu|first2=Mihaela|publisher=Shutter Waves|year=2018|isbn=978-1-947641-17-4|edition=First|location=Parker, TX|access-date=29 January 2020}}</ref> |
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<gallery widths="230px" heights="230px"> |
<gallery widths="230px" heights="230px"> |
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Soubor:Fluorite Structure.jpg|Fluoridová struktura u [[fluorid vápenatý|fluoridu vápenatého]], CaF<sub>2</sub><ref name=Costel/> |
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Soubor:Antifluorite Structure.jpg|Antifluoritová struktura silicidu hořečnatého, Mg<sub>2</sub>Si<ref name=Costel/> |
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{| class="wikitable" |
{| class="wikitable" |
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|+ |
|+Mřížkové konstanty látek s fluoritovou a antifluoritovou strukturou při 300 K<ref name=Costel/> |
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! Látka !! Mřížková konstanta (pm) !! Krystalová struktura |
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|BaF<sub>2</sub>||6 |
|[[Fluorid barnatý|BaF<sub>2</sub>]]||619,6|| fluoritová |
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|{{nowrap|1=''β''-}}PbF<sub>2</sub>|| |
|{{nowrap|1=''β''-}}[[Fluorid olovnatý|PbF<sub>2</sub>]]||594|| fluoritová |
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|PuO<sub>2</sub>|| |
|[[Oxid plutoničitý|PuO<sub>2</sub>]]||539,9|| fluoritová |
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|SrF<sub>2</sub>|| |
|SrF<sub>2</sub>||579,96|| fluoritová |
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|[[ |
|[[oxid uraničitý|UO<sub>2</sub>]]||547,065|| fluoritová |
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|CaF<sub>2</sub>|| |
|[[Fluorid vápenatý|CaF<sub>2</sub>]]||546,3|| fluoritová |
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|[[ |
|[[oxid zirkoničitý|ZrO<sub>2</sub>]]||514|| fluoritová |
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|K<sub>2</sub>O|| |
|[[Oxid draselný|K<sub>2</sub>O]]||644,9|| antifluoritová |
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|K<sub>2</sub>S|| |
|[[Sulfid draselný|K<sub>2</sub>S]]||740,6|| antifluoritová |
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|Li<sub>2</sub>O|| |
|[[Oxid lithný|Li<sub>2</sub>O]]||461|| antifluoritová |
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|Na<sub>2</sub>O|| |
|[[Oxid sodný|Na<sub>2</sub>O]]||555|| antifluoritová |
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|Na<sub>2</sub>S|| |
|[[Sulfid sodný|Na<sub>2</sub>S]]||654|| antifluoritová |
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|Rb<sub>2</sub>O|| |
|[[Oxid rubidný|Rb<sub>2</sub>O]]||674|| antifluoritová |
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|Mg<sub>2</sub>Si|| |
|Mg<sub>2</sub>Si||633,8|| antifluoritová |
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== Reference == |
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== Calcium fluoride example == |
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Crystallography is a powerful tool to investigate the structures of crystalline materials. It is important to understand the crystal structure of materials to form structure-property relationships. These relationships can help predict the behavior of crystalline materials, as well as introduce the ability to tune their properties. Calcium fluoride is a classic example of a crystal with a fluorite structure. Crystallographic information can be collected via x-ray diffraction, providing information on the locations of electron density within a crystal structure. Using modern software such as Olex2,<ref>{{cite web|title=OlexSys |url=https://www.olexsys.org/about/|website=OlexSys}}</ref> one can solve a crystal structure from crystallographic output files. |
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<gallery widths="300px" heights="300px"> |
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File:calciumfluoritecrystal.jpg|Extended crystal structure of calcium fluoride showing octahedral crystal. |
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</gallery> |
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=== Views of calcium fluoride crystal structure === |
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In calcium fluoride, the calcium cations are surrounded by fluorine anions that occupy the tetrahedral sites, with an 8:4 coordination number, fluorine to calcium. This ratio is consistent with the stoichiometry of the compound, where the ratio of fluorine to calcium is 2:1. This relationship can be visualized as a cubic array of anions surrounding the calcium cations. |
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<gallery widths="250px" heights="250px"> |
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File:CaF2_polyhedra2.jpg|Cubic corner sharing visualization of calcium fluoride. Calcium in blue, fluorine in green. |
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File:CaF2_polyhedra3.jpg|Cubic corner sharing visualized down a separate axis. |
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</gallery> |
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=== Extended fluorite structure === |
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Beyond the until cell, the extended crystal structure of fluorite continues packing in a face-centered cubic (fcc) packing structure (also known as cubic close-packed or ccp).<ref>{{cite book |last1=Shriver |display-authors=etal |title=Inorganic Chemistry |date=January 2014 |publisher=Oxford University Press |isbn=978-1-4292-9906-0 |edition=Sixth}}</ref> This pattern of spherical packing follows an ABC pattern, where each successive layer of spheres settles on top of the adjacent hole of the lattice. In contrast, hexagonal close-packed (hcp), are successively layered with an ABAB pattern. These two types of packing are the most closely packed forms of spherical packing.<ref>{{cite web |last1=Redwing |first1=Ronald |title=Face Centered Cubic Structure (FCC) |url=https://www.e-education.psu.edu/matse81/node/2133 |website=The Pennsylvania State University}}</ref> |
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<gallery widths="250px" heights="250px"> |
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File:CaF2_extenda.jpg|Extended crystal stacking structure of calcium fluoride; unit cell expanded by a unit of 3. |
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File:CaF2_pol1.jpg|View of extended packing structure of calcium fluoride down a separate axis; expanded unit cell. |
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</gallery> |
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{{Překlad | jazyk = en | článek = Fluorite structure | revize = 1170371243}}<references /> |
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==See also== |
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* [[Cubic crystal system#Rock-salt structure|Rock-salt structure]] |
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{{Portály|Chemie}} |
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==References== --> |
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[[Kategorie:Fluorit]] |
[[Kategorie:Fluorit]] |
Aktuální verze z 27. 7. 2024, 19:27
Fluoritová struktura je druh struktury sloučenin odpovídajících vzorci MX2.[1] Ionty X obsazují osm tetraedrických míst a ionty M vytvářejí plošně centrovanou krychlovou strukturu. Pojmenována je podle fluoritu (CaF2).
Řada sloučenin se vzorcem M2X má antifluoritovou strukturu, kdy jsou polohy aniontů a kationtů oproti fluoritu prohozené, takovou látkou je například silicid hořečnatý, Mg2Si, v němž je každý silicidový anion obklopen osmi hořečnatými kationty a každý hořečnatý kation sousedí se čtyřmi silicidovými anionty.[2]
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Fluoridová struktura u fluoridu vápenatého, CaF2[2]
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Antifluoritová struktura silicidu hořečnatého, Mg2Si[2]
Látka | Mřížková konstanta (pm) | Krystalová struktura |
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BaF2 | 619,6 | fluoritová |
β-PbF2 | 594 | fluoritová |
PuO2 | 539,9 | fluoritová |
SrF2 | 579,96 | fluoritová |
UO2 | 547,065 | fluoritová |
CaF2 | 546,3 | fluoritová |
ZrO2 | 514 | fluoritová |
K2O | 644,9 | antifluoritová |
K2S | 740,6 | antifluoritová |
Li2O | 461 | antifluoritová |
Na2O | 555 | antifluoritová |
Na2S | 654 | antifluoritová |
Rb2O | 674 | antifluoritová |
Mg2Si | 633,8 | antifluoritová |
Reference
[editovat | editovat zdroj]V tomto článku byl použit překlad textu z článku Fluorite structure na anglické Wikipedii.
- ↑ GREENWOOD. Chemistry of the Elements. 2. vyd. [s.l.]: Elsevier Science & Technology Books, 1997. Dostupné online. ISBN 978-0-08-037941-8. (anglicky)
- ↑ a b c d Costel Rizescu; Mihaela Rizescu. Structure of Crystalline Solids, Imperfections and Defects in Crystals. [s.l.]: Shutter Waves, 2018. Dostupné online. ISBN 978-1-947641-17-4.