Perovskite

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This article is about the mineral. For synthetic compounds, see Perovskite (structure). For solar cells using perovskite-structured compounds, see Perovskite solar cell.
Perovskite
Specific gravity
3.98–4.26
Optical propertiesBiaxial (+)
Refractive indexnα = 2.3, nβ = 2.34, nγ = 2.38
Other characteristicsnon-radioactive, non-magnetic
References[2][3][4][5]

Perovskite (pronunciation:

cations can be embedded in this structure, allowing the development of diverse engineered materials.[7]

History

The mineral was discovered in the

Helen Dick Megaw.[9]

Occurrence

Found in the Earth's

ultramafic rocks and foidolites, due to the instability in a paragenesis with feldspar. Perovskite occurs as small anhedral to subhedral crystals filling interstices between the rock-forming silicates.[10]

Perovskite is found in

Ca-Al-rich inclusions found in some chondritic meteorites.[4]

The stability of perovskite in

volcanic rocks perovskite and sphene are not found together, the only exception being an etindite from Cameroon.[12]

A

Alnö, Sweden. A niobium-bearing variety dysanalyte occurs in carbonatite near Schelingen, Kaiserstuhl, Germany.[11][13]

In stars and brown dwarfs

In

L-dwarfs.[14][15]

Physical properties

Crystal structure of perovskite CaTiO3; red=oxygen, grey=titanium, blue=calcium

The eponymous Perovskite CaTiO3 crystallizes in the Pbnm space group (No. 62) with lattice constants a = 5.39 Å, b = 5.45 Å and c = 7.65 Å.[16]

Perovskites have a nearly cubic structure with the general formula ABO3. In this structure the A-site ion, in the center of the lattice, is usually an alkaline earth or rare-earth element. B-site ions, on the corners of the lattice, are 3d, 4d, and 5d transition metal elements. The A-site cations are in 12-fold coordination with the anions, while the B-site cations are in 6-fold coordination. A large number of metallic elements are stable in the perovskite structure if the Goldschmidt tolerance factor t is in the range of 0.75 to 1.0.[17]

where RA, RB and RO are the ionic radii of A and B site elements and oxygen, respectively. The stability of perovskites can be characterized with the tolerance and octahedral factors. When conditions are not fulfilled, a layered geometry for edge-sharing or face-sharing octahedra or lower B-site coordination is preferred. These are good structural bounds, but not an empirical prediction.[18]

Perovskites have sub-metallic to

orthorhombic system, as is the case for CaTiO3 (strontium titanate, with the larger strontium cation in the A-site, is cubic). Perovskite crystals have been mistaken for galena; however, galena has a better metallic luster, greater density, perfect cleavage and true cubic symmetry.[19]

Perovskite derivatives

Double perovskites

A double perovskite has a formula of A'A"B'B"O6 and replaces half the B sites with B′, where A are alkaline or rare earth metals and B are transition metals. The cation arrangement will differ based on charge, coordination geometry, and the ratio between A cation and B cation radii. The B and B′ cations lead to different ordering schemes. These ordering schemes are rock salt, columnar, and layered structures.[20] Rock salt is an alternating, three-dimensional checkerboard of B and B' polyhedra. This structure is the most common from an electrostatic point of view, as the B sites will have different valence states. Columnar arrangement can be viewed as sheets of B-cation polyhedral viewed from the [111] direction. Layered structures are seen as sheets of B′ and B polyhedra.

Lower dimensional perovskites

3D perovskites form when there is a smaller cation in the A site so BX6 octahedra can be corner shared. 2D perovskites form when the A-site cation is larger so octahedra sheets are formed. In 1D perovskites, a chain of octahedra is formed[21] while in 0D perovskites, individual octahedra are separated from each other. Both 1D and 0D perovskites lead to quantum confinement[22] and are investigated for lead-free perovskite solar cell materials.[23]

See also

References

  1. S2CID 235729616
    .
  2. ^ "Prehnit (Prehnite)". Mineralienatlas.de.
  3. ^ a b "Perovskite". Webmineral.
  4. ^ a b Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (eds.). "Perovskite" (PDF). Handbook of Mineralogy. Chantilly, VA: Mineralogical Society of America.
  5. ISBN 978-81-308-0070-7
    .
  6. ISBN 978-0-521-52958-7
    .
  7. PMID 29123058
    .
  8. S2CID 33792511
    .
  9. S2CID 4096136
    .
  10. ^ Chakhmouradian, Anton R.; Mitchell, Roger H. (1998). "Compositional variation of perovskite-group minerals from the Khibina Complex, Kola Peninsula, Russia" (PDF). The Canadian Mineralogist. 36: 953–969.
  11. ^ a b Palache, Charles, Harry Berman and Clifford Frondel, 1944, Dana's System of Mineralogy Vol. 1, Wiley, 7th ed. p. 733
  12. doi:10.1016/0024-4937(90)90047-5
    .
  13. ISBN 978-0-582-30094-1
    .
  14. S2CID 14944231
    .
  15. ISSN 0004-637X
    .
  16. ISSN 0108-7681
    .
  17. PMID 11710238.[permanent dead link
    ]
  18. PMID 29735683
    .
  19. S2CID 97682597.[permanent dead link
    ]
  20. S2CID 214470882
    .
  21. hdl:10281/352629
    .
  22. S2CID 234172920
    .
  23. S2CID 236391984
    .

External links
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