Perovskite
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Perovskite structure. The red spheres are oxygen atoms, the deep blue are smaller (Ca2+) metal cations and the green/blue are the larger (Ti4+) metal cations
Perovskite structure. The red spheres are oxygen atoms, the deep blue are smaller (Ca2+) metal cations and the green/blue are the larger (Ti4+) metal cations

Perovskite (calcium titanium oxide, CaTiO3) is a relatively rare mineral on the Earth's crust. Perovskite crystallizes in the orthorhombic (pseudocubic) crystal system. Perovskite was discovered in the Ural mountains of Russia by Gustav Rose in 1839 and is named after Russian mineralogist, L. A. Perovski (1792-1856).

Perovskite is also the name of a more general group of crystals which take the same structure. The basic chemical formula follows the pattern ABO3, where A and B are cations of different sizes (for example, LaMnO3). Formed under the high pressure conditions of the Earth's mantle, the pyroxene enstatite is a perovskite-structured polymorph of MgSiO3, and may be the most common mineral in the Earth.[1]

Perovskite materials are used as catalyst electrodes in certain types of fuel cells.

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Structure

The perovskite structure is adopted by many oxides that have the chemical formula ABO3. The structure is very versatile having many useful technological applications such as ferroelectrics, catalysts, sensors, thermopower and superconductors.

The general crystal structure is a primitive cube, with the B cation in the middle of the cube, the A cation in the corner and the anion, commonly oxygen, in the centre of the face edges. The structure is stabilized by the 6-fold coordination of the B cation (octahedron) and 12-fold coordination of the A cation. The packing of the ions can be thought of as the A and O ions together forming a cubic close-packed array, where the B ions occupy a quarter of the octahedral spaces.

Although the primitive cube is the idealized structure, differences in radius between the A and B cations can alter the structure to a number of different so-called distortions, of which tilting is the most common one. With perovskite tilt the BO6 octahedron twists along one or more axes to accommodate the difference.

Complex perovskite structures contain two different B-site cations. This results in ordered and disordered variants.

The perovskite structure shares the property of ferroelectricity with garnet and olivine. Many superconducting ceramic materials have perovskite-like structures.

Occurrences

Perovskite is found in contact metamorphic rocks and associated mafic intrusives.

It is found in some silica-undersaturated igneous rocks, such as nepheline syenite and melilitite, and rare carbonatites.

Perovskite also is a common mineral in the Ca-Al-rich inclusions (CAIs) found in some chondritic meteorites.

See also

References

  1. ^ John Lloyd; John Mitchinson. "What's the commonest material in the world", QI: The Book of General Ignorance. Faber & Faber. ISBN 0-571-23368-6. 
  • Moty Schultz and Lior Klein, Physical Review B 73, 085109 (2006).
  • Tejuca, Luis G (1993). Properties and applications of perovskite-type oxides. New York: Dekker, 382. ISBN 0-8247-8786-2. 
  • Mitchell, Roger H (2002). Perovskites modern and ancient. Thunder Bay, Ontario: Almaz Press, 318. ISBN 0-9689411-0-9. 

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