SPINELS,INVERSE SPINELS AND PEROVSKITES

A simple compile of crystal structures: SPINELS,INVERSE SPINELS AND PEROVSKITES.

1. SOLID STATE 1.SPINELS AND INVERSE SPINELS 2. Perovskites BY SHOBANA.N.S QUEEN MARY’S COLLEGE

2. Spinel Spinels generally refer to metal oxides having general formula AB 2 X 4 T he spinel that is most popularly known is MgAl 2 O 4

3. Where A II = a divalent cation like Mg, Cr, Mn, Fe, Co, Ni , Cu, Zn, Cd, Sn  B III = a trivalent cation like Al, Ga, In, Ti, V, Cr, Mn, Fe, Fe, Co, Ni  X = O, S, Se etc. AB 2 X 4

4. Crystal Structure of Spinels Normal spinel structures are usually cubic close-packed oxides with one octahedral and two tetrahedral sites per formula unit. B 3+ ions occupy half the octahedral holes, while A 2+ ions occupy one-eighth of the tetrahedral holes.

5. Examples In 4 SnS 8 a nd MgAl 2 O 4 OTHER EXAMPLES: Mn 3 O 4 , ZnFe 2 O 4 , FeCr 2 O 4 (chromite) etc

6. Their crystalline structure is identical to natural spinel , So surprisingly, they can mimic the blues of aquamarine, zircon or blue topaz, and blue sapphire.

7. Presence of Cations Let us consider the case of ZnCr   2   O   4 ZnCr   2   O   4 ZnCr   2   O   4 ZnCr 2 O 4 Zn   +2   d-10 ion with CFSE = 0 and thus, there will be no effect on Oh holes. Cr   +3     d-3 ion with CFSE = -8Dq and hence this cations will occupy the Oh holes. Hence higher the CFSC value, greater is its tendency to occupy octahedral hole.

8. Applications Due to greater refractive index, spinels are generally used as Gemstones. These spinel gemstones are considered very rare and precious. 398.72-carat Catherine the Great’s ruby Black Prince’s ruby Timur Ruby

9. Samarian Spinel The fourth largest Spinel. It is a 500-carat spinel gemstone.

10. Other Applications Spinels are generally used in TV and Phone screens.

11. Used as superconducting magnet in MRI and NMR Super magnets

12. Inverse Spinel This picture compares the crystal structure of inverse Spinels with spinels .

13. STRUCTURAL ARRANGEMENT Inverse Spinels usually have alternate arrangement. The A II ions occupy the octahedral voids, whereas half of B III ions occupy the tetrahedral voids It can be represented as: (B III ) tet (A II B III ) oct O 4   Most ferrite follow this structure such as Fe 3 O 4 (or FeO.Fe 2 O 3 ), NiFe 2 O 4 , CoFe 2 O 4 etc

14. MAGNETIC PROPERTY

15. CONCLUSION

16. APPLICATION Iron oxide nanoparticles: Iron oxide nanoparticles are iron oxide particles with diameters between about 1 and 100 nanometers. The two main forms are magnetite ( Fe 3 O 4 ) and its oxidized form maghemite ( γ- Fe 2 O 3 ). They have attracted extensive interest due to their super paramagnetic properties

17. Perovskites They are ternary oxides of general formula ABX 3. where the anion X can be O, N, or F. The A ions are typically large ions such as Sr 2+ , Ba 2+ , Rb + , or a lanthanide 3+ ion The B ions are smaller transition metal ions such as Ti 4+ , Nb 5+ , Ru 4+ , etc A,B,X- White, Blue and Red

18. Examples are many titanates like BaTiO 3 , SrTiO 3 , PbTiO 3 etc. which happen to be technologically very useful compounds Examples

19. TYPES OF PEROVSKITES Perovskites can also have various combinations of ionic valence such as e.g. A 2+ B 4+ O 4 , BaTiO 3, PbTiO 3 , CaTiO 3 , SrTiO 3 etc . e.g. A 3+ B 3+ O 4 , LaAlO 3 , LaGaO 3 , BiFeO 3 etc . Mixed Perovskites : A 2+ (B 2+ 1/3 B 5+ 2/3 )O 3 e.g.. Pb (Mg 1/3 Nb 2/3 )O 3 A 2+ (B 3+ 1/2 B 5+ 1/2 )O 3 e.g.. Pb (Sc 1/2 Ta 1/2 )O 3

20. APPLICATION Perovskites solar cells: A perovskite solar cell is a type of solar cell which includes a perovskite absorber. This act as the light-harvesting active layer, which produces electricity from sunlight. Perovskite absorber materials are extremely cheap to produce and simple to manufacture

21. Lasers In 2014 researchers demonstrated that perovskite can generate laser light Methyl ammonium lead iodide perovskite (CH 3 NH 3 PbI 3 - x Cl x ) cells fashioned into optically pumped vertical-cavity surface-emitting lasers (VCSELs) convert visible pump light to near-IR laser light with a 70 % efficiency. [

22. Photo electrolysis Water electrolysis at 12.3 % efficiency in a highly efficient and low-cost water-splitting cell using perovskite photovoltaics

23. THANK YOU!!!