1 / 20

Vizualizarea structurilor

Vizualizarea structurilor. Cristobalit (SiO 2 ). Reprezentare atomica. Poliedre de coordinare. Topologia. Bragg jun. (1920). Pauling (1928). Wells (1954). Topologie. Crystal data Formula sum Mg 2 SiO 4 (Olivine) Crystal system orthorhombic Space group P b n m (no. 62)

selima
Download Presentation

Vizualizarea structurilor

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Vizualizarea structurilor Cristobalit (SiO2) Reprezentare atomica Poliedre de coordinare Topologia Bragg jun. (1920) Pauling (1928) Wells (1954)

  2. Topologie Crystal data Formula sum Mg2SiO4 (Olivine) Crystal system orthorhombic Space group P b n m (no. 62) Unit cell dimensions a = 4.75(2) Å, b = 10.25(4) Å, c = 6.00(2) Å Z 4 Atomic coordinates Atom Ox. Wyck. x y z Mg1 +2 4a 0.00000 0.00000 0.00000 Mg2 +2 4c 0.00995(600) 0.27734(600) 0.75000 Si1 +4 4c 0.07373(500) 0.4043(50) 0.25000 O1 -2 4c 0.23242(1000) 0.0918(100) 0.75000 O2 -2 4c 0.2793(100) 0.05078(1000) 0.25000 O3 -2 8d 0.22266(1000) 0.33594(1000) 0.46289(1000) http://rruff.geo.arizona.edu/AMS/amcsd.php

  3. Tipuri de impachetari Impachetare cubica compacta(low space filling) Impachetare hexagonala compacta(high space filling)

  4. strat A A A A A A B C C A A A A A A B B strat B C A A A A A strat C Impachetare cubica compacta ABCABC... Impachetare hexagonala compacta ABAB... Arhetipuri structurale Coordinari. Poliedrii de coordinare

  5. ABC ABAB

  6. Goluri octaedrice Goluri tetraedrice

  7. Impachetare cubica simpla (atomi identici) Metale (SCP) (Fe, Cr, Mo, W, Ta, Ba ...) Acoperire spatiu= 68% NC = 8

  8. Arhetipuri structurale conventie: anionii formeaza impachetarea ABAB, ABCA.., cationi in golurile tetraedrice si octaedrice

  9. Arhetipuri structurale Tipul NaCl RC:RA= 0.73÷0.41 NC=6 • Caracteristicistructurale: • Structura tip ABC (CCP) • Na estecoordinat de 6 Cl, Clestecoordinat de 6 Na • Un octaedru NaCl6estecoordinat de 12 octaedrii NaCl6 • Octaedrii se conecteazaprinmuchii Ex.: silvina KCl, alabandina MnS, galena PbS

  10. Arhetipuri structurale Tipul NaCl Pirita FeS2 • Perechile S2 in pozitiile Na din str. halitului Calcit CaCO3 • un cub deformat pe directia axului c; • Gruparile CO3 in pozitiile Na din str. halitului

  11. Arhetipuri structurale Tipul CsCl RC:RA> 0.73 NC=8 • Caracteristicistructurale: • Structura tip AAA (SCP) - anioniiocupacolturileunui cub iarcationiiocupaintestitiile;

  12. Arhetipuri structurale Tipul CaF2 - fluorina RC:RA>0.73 Ca – in colturile unei retele cubice F – centrele celor 8 cuburi in care poate fi impartita celula →vacante structurale→clivaj octaedric • Caracteristicistructurale: • impachetareCCP (ABC) • F coordinattetraedric 4 Ca • Ca is coordinat cubic de 8 F Ex. halogenuri, oxizi ≠CsCl → Ca2+ Structurile NaCl, CaF2, CsCl sunt cubice si difera prin tipul de impachetare datorat contrastelor de raze cation/anion (vezi raporturi de raze ionice si coordinari) si sarcina cationului (Na+, Ca2+, Cs+).

  13. Arhetipuri structurale Tipul sphalerite → structura de tip “cub centrat pe fete” formata de atomii de S (galben) si Zn in centrul fiecarui tetraedru (violet). RC:RA= 0.32 • Caracteristicistructurale: • structura tip diamant (in sphalerit, ½ din pozitiisuntocupate de Zn/S) un cub ocupat de 4 tetraedrii, cu varfurileindreptate in aceeasidirectie (Desenati!) • impachetare CCP (ABC) Ex. calcopirita, tetraedrit

  14. Calcopirita - Celula elementara cu atomi Fe (portocaliu) alternaeaza cu celule continand Cu (albastru). Aceasta alternanta determina aparitia simetriei tetragonale. Mimeaza simetria cubica →cristale tetraedrice

  15. Arhetipuri structurale Rutil (TiO2) Ti – coordinat octaedric de O (NC=6) O – coordinat de 3 Ti (NC=3) • Caracteristicistructurale: • HCP (ABAB…) • Lanturioctaedrice II c RC:RA=0.73-0.41 Ex. stishovit SiO2

  16. Structuri complexe perovskite (SrTiO3) ABO3 • Caracteristicistructurale: • CCP • O2-impachetatCCP; ¼ inlocuiti cu cationi R> in coordinare 10 (cationi A); • Cationii B – coordinatioctaedric; • Valentele A,B – nespecificate (suma +6) • Structurifoarte dense - manta

  17. Arhetipuri structurale Spinel (MgAl2O4) AB2O4 • Caracteristicistructurale: • retea CCP formata de O • 1/8 din pozitiiletetraedrice - A • ½ din pozitiileoctaedrice - B • A,B – valentediferite A:B=2:1

  18. Structuri complexe Silicati • Caracteristicistructurale: • unitatestructurala: tetraedrul SiO4 • tetraedriiizolatisauconectatiprincolturi • Tetraedrii TO4, octaedrii MO6, (M = Fe, Al, Mg, Co, Ni…) Ciclosilicati Nezosilicati Sorosilicati SiO44- Olivine: (Mg,Fe)2SiO4 Si2O76- Thortveitite: (Sc,Y)2Si2O7 SiO32- Beryl: Be3Si6O18

  19. Structuri complexe Silicati Inosilicati Filosilicati Si2O52- Biotit: K(Mg,Fe)3AlSi3O10(OH)2 Lant simplu: SiO32- Piroxen: (Mg,Fe)SiO3 Lant dublu: Si4O116- Tremolit: Ca2(Mg,Fe)5Si8O22(OH)2

  20. Structuri complexe Silicati Tectosilicati SiO2 Faujasit: Ca28Al57Si135O384 carcasa (cage) reprezentare T

More Related