SPINELS,INVERSE SPINELS AND PEROVSKITES

SOLID STATE1.SPINELS AND INVERSE SPINELS

2. PEROVSKITESBY

SHOBANA.N.S

QUEEN MARY’S COLLEGE

Spinel

• Spinels generally refer to metal oxides having

general formula AB2X4

• The spinel that is most popularly known is

MgAl2O4

Where

AII = a divalent cation like Mg, Cr, Mn, Fe, Co,

Ni, Cu, Zn, Cd, Sn

BIII = a trivalent cation like Al, Ga, In, Ti, V, Cr, Mn,

Fe, Fe, Co, Ni

X = O, S, Se etc.

AB2X4

Crystal Structure of Spinels

Normal spinel structures are usually cubic

close-packed oxides with one

octahedral and two tetrahedral sites per

formula unit.

B3+ ions occupy half the octahedral

holes, while A2+ ions occupy one-eighth

of the tetrahedral holes.

Examples In4SnS8 and MgAl2O4

OTHER EXAMPLES:

Mn3O4, ZnFe2O4,

FeCr2O4

(chromite) etc

Their crystalline

structure is identical

to natural spinel, So

surprisingly, they can

mimic the blues of

aquamarine, zircon

or blue topaz, and

blue sapphire.

Presence of Cations

Let us consider the case of

ZnCr 2 O 4

ZnCr 2 O 4

ZnCr 2 O 4

ZnCr2O4

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.

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

Samarian Spinel

• The fourth largest Spinel.

• It is a 500-carat spinel

gemstone.

Other Applications

Spinels are generally used in TV and Phone screens.

Used as superconducting magnet in MRI and NMR

Super magnets

Inverse Spinel

This picture compares the

crystal structure of inverse

Spinels with spinels.

STRUCTURAL ARRANGEMENT

Inverse Spinels usually have alternate arrangement.

The AII ions occupy the octahedral voids, whereas half of BIII ions occupy the tetrahedral voids

It can be represented as: (BIII)tet(AIIBIII)octO4

Most ferrite follow this structure such as

Fe3O4 (or FeO.Fe2O3), NiFe2O4, CoFe2O4 etc

MAGNETIC PROPERTY

CONCLUSION

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 (Fe3O4) and its

oxidized form maghemite (γ-Fe2O3).

They have attracted extensive interest due to their super paramagnetic properties

Perovskites

They are ternary oxides of general formula ABX3.

where the anion X can be O, N, or F.

The A ions are typically large ions such as Sr2+, Ba2+,

Rb+, or a lanthanide 3+ ion

The B ions are smaller transition metal ions such

as Ti4+, Nb5+, Ru4+, etc

A,B,X- White, Blue and Red

Examples are many titanates like BaTiO3, SrTiO3, PbTiO3 etc. which happen

to be technologically very useful compounds

Examples

TYPES OF PEROVSKITES

Perovskites can also have various combinations of ionic valence such as

• e.g. A2+B4+O4 , BaTiO3, PbTiO3, CaTiO3, SrTiO3 etc.

• e.g. A3+B3+O4 , LaAlO3, LaGaO3, BiFeO3 etc.

Mixed Perovskites:

• A2+(B2+1/3B

5+2/3)O3 e.g.. Pb(Mg1/3Nb2/3)O3

• A2+(B3+1/2B

5+1/2)O3 e.g.. Pb(Sc1/2Ta1/2)O3

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

Lasers

In 2014 researchers demonstrated that perovskite can generate laser light

Methyl ammonium lead iodide perovskite (CH3NH3PbI3-xClx)

cells fashioned into optically pumped

vertical-cavity surface-emitting lasers (VCSELs) convert

visible pump light to near-IR laser light with a 70% efficiency.[

Photo electrolysis

Water electrolysis at 12.3% efficiency in a highly efficient and low-cost

water-splitting cell using perovskite photovoltaics

THANK YOU!!!