GARNETS AND PEROVSKITES

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MAGNETIC MATERIALSGARNETS AND PEROVSKITES
Sujith Varghese M140057CY
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GARNETS
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• Garnets are large family of complex oxides.
• General formula A3B2X3O12
• A Y,Sm,Gd,Tb,Dy,Ho,Er,Tm,Yb,Lu.
• Coordination number8 in a distorted cubic
  environment.
• B and X are smaller ions which occupy Oh and Td
  sites, respectively.

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STRUCTURE
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• Schematic of the cubic unit cell of Y3Fe5O12
  (YIG) garnet structure.
• 8 formula units per unit cell i.e., 160 atoms in
  the unit cell.
• 24 c-sites, 16 a-sites, 24 d-sites, 96 h-sites in
  a unit cell.

Google images.
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A B X COMBINATIONS
Grossular Ca3Al2Si3O12
Uvarovite Ca3Cr2Si3O12 Pyrope
Mg3Al2Si3O12
Andradite Ca3Fe2Si3O12 YIG
Y3Fe5O12 Almandine
Fe3Al2Si3O12 Images adapted from Wikipedia.org
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MAGNETIC PROPERTIES
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• Basic requirement magnetic cations in d and a
  sites.
• d-site cations sublattice are coupled
  ferromagnetically.
• a-site and c-site cations sublattices coupled
  ferromagnetically.
• d-site and a-site cations sublattices coupled
  antiferromagnetically.
• The net magnetic moment,
• MMd-Ma-Mc

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• Consider ,Yttrium Iron Garnet (YIG), Y3Fe5O12
• Y3 is a d0 ion, it has no magnetic
  moment.
• Fe3 occupies both 16(a) and 24(d) sites
• The magnetic moment per YIG molecule,
• M
  3Fe3 - 2Fe3 5µB
• YIG and other rare earth garnets are
  ferrimagnetic with a Tc 548K to578K
• Saturation magnetization of yttrium gadolinium
  iron garnet
• (Y3-3xGd3x)Fe2Fe3O12

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From Ref. 2
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• Doped YIG crystals show variation in saturation
  magnetization with temperature.
• There is a temperature at which M0, called
  Compensation temperature(Tcomp).
• Tcomp increases with increased substitution of
  Gd3 for Y3.
• Above Tcomp, contribution from c-sublattice
  diminishes .
• With appropriate substitution it is possible to
  prepare variety of garnet magnetic materials for
  specific purposes.

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From Ref. 2
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APPLICATIONS
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• microwave YIG filters.  
• Solid-state lasers.
• Faraday rotators.
• Data storage.

Images adapted from Wikipedia.org
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PEROVSKITES
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• The mineral perovskite (CaTiO3) is named after
  Russian mineralogist, Count LevAleksevich von
  Perovski, and was discovered and named by Gustav
  Rose in 1839 from samples found in the Ural
  Mountains.
• CaTiO3
  Perovski Gustav Rose
• Images adapted from Wikipedia.org

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• Class of compounds, which have the same type of
  crystal structure as CaTiO3, known as the
  perovskites.
• General Formula ABO3

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A network of corner-sharing BO6 octahedra with a
large A-site cation occupying the interstitial
position is shown.
(a) A network of corner-sharing BO6 octahedra
with a large A-site cation occupying the
interstitial position is shown. (b) The
simplified unit-cell representation of cubic
perovskite without showing coordination. (c) The
geometry of the building units, AO12 cuboctahedra
and BO6 octahedra, with 12-coordinated A-site and
6-coordinated B-site, respectively.
Prasanna V. Balachandran et al. Proc. R. Soc. A
20114672271-2290
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2011 by The Royal Society
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MAGNETIC PROPERTIES
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• Perovskites with transition metal ions (TMI) on
  the B site show an enormous variety of magnetic
  properties.

Google images.
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• LaMnO3 is an insulating, antiferromagnetic (AFM)
  compound.
• La1-xSrxMn31-xMn4xO3 becomes ferromagnetic
  with a well-defined Curie temperature at a finite
  x, and metallic below TC

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From Ref. 3
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APPLICATIONS
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• Perovskite solar cell
• Lasers
• LEDS
• Photoelectrolysis

Google images
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REFERENCES
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• Solid State Chemistry and its Applications, 2nd
  Edition, Student Edition, Anthony R. West.
• Microwave Materials edited by V.R.K. Murthy, S.
  Sundaram, B. Viswanathan, Google Books.
• Study of the giant electroresistance in epitaxial
  thin films of La0.9Sr0.1MnO3, Yao, Hui 2005.
• Prasanna V. Balachandran et al. Proc. R. Soc. A
  20114672271-2290.
• Wikipedia.org

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THANK YOU
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