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Ca[TiO3] A natural, yellow, brownish-yellow, reddish, brown, or black mineral and a structure type which includes no less than 150 synthetic compounds; the crystal structure is ideally cubic, it occurs as rounded cubes modified by the octahedral and dodecahedral forms, luster is subadamantine to submetallic, hardness is 5.5 on Mohs scale, and specific gravity is 4.0.



(named for L. A. Perovskii). (1) A mineral of the oxide class. The chemical formula of perovskite is CaTiO3, with CaO accounting for 41.24 percent of the composition, and TiO2 for 58.76 percent. Perovskite that contains admixtures of Ce is called knopite; of Ni, Ce, and Fe, dysanalite; and of Na, Ce, Ti, and Nb, loparite.

Perovskite crystallizes in the pseudoisometric system. Each calcium atom is surrounded by 12 oxygen atoms, which are located at the apexes of a cuboctahedron; the coordination number of Ti is eight. Characteristic striations appear on the cubic faces parallel to the edges. Cleavage is cubic, hardness is 5.5–6 on Mohs’ scale, and the density ranges from 3,950 to 4,040 kg/m3. The color may be black, grayish black, or brownish.

Perovskite frequently occurs in ultrabasic alkaline rocks, including olivinites, pyroxenes, and kimberlites, as well as in associated ore segregations and carbonatites. It fills the interstices at the point of contact of basic rocks with limestone; it also is interstitially distributed in chloritic shale and in nephelinic, leu-citic, and melilitic basalts.

Knopite is used as a source of rare-earth elements of the cerium group, and loparite is a source of niobium and titanium.

(2) A group of chemical compounds whose crystal structure resembles that of perovskite [in English usage “perovskite” is the adjectival noun that denotes the structure type of these compounds and not the compounds themselves]. Perovskites have the general formula ABX3, where A is a tetravalent cation, B is a heptavalent cation, and X is an anion—usually oxygen, as in NaNbO3 and BaTiO3. Many of these compounds are ferroelectric, including BaTiO3 and LiNbO3; the group also includes some superconductors (for example, SrTiO3), semiconductors, and compounds that display magnetic ordering.


An oxide mineral made up of calcium titanate that is expected to be commercialized in higher-efficiency solar cells in the 2020-2021 time frame. Named after Russian mineralogist Lev Perovski, who discovered it in the 1800s, perovskite may also be employed as quantum dots in future screen technologies due to its high color purity. See quantum dot.

Automatic Solar Cell Window Shades
In 2018, using perovskite and carbon nanotube technologies, the National Renewable Energy Lab in Golden, Colorado developed clear window glass that emits electricity and darkens with sunshine. When the sun fades, the window becomes transparent again. The transparency range is 3% to 68%.
References in periodicals archive ?
But the surface of hybrid perovskites is prone to surface defects, or surface traps, where charge carriers are trapped in the semiconducting material.
Perovskites are semiconductor materials that have many applications.
The offhand comment led the team to recall that the caffeine in coffee is an alkaloid compound containing molecular structures that could interact with the precursors of perovskite materials -compounds with a particular crystal structure that forms the light-harvesting layer in a class of solar cells.
In order to continue enhancing the solar cells' efficiency and stability, the team next plans to further investigate the chemical structure of the caffeine-incorporated perovskite material and to identify the best protective materials for perovskites.
Furthermore, Case and others argue, the amount of lead in perovskites is trivial, because of how little perovskite is involved.
Electrical properties of the oxygen-deficient perovskites, [Ca.sub.2][Mn.sub.2-x][Nb.sub.x][O.sub.[gamma]] : 0 [less than or equal to] x [less than or equal to] 1.2, with Mn valence varying from +2.0 to +4.0.
Although some other perovskite cells are more efficient, Zhou's invention is important because it makes the manufacturing process easier and cheaper.
In particular, they have been extensively employed in perovskite solar cells (PSCs) [1-3], contributing to boost their impressive evolution in the last ten years from an initial 3.8% [4] to a 22.1% [5] certified efficiency.
We have reported the scaling behavior and related physical growth dynamics of [MAPbI.sub.3] perovskite thin films on smooth Si substrates [11].
It is worth noting that reaction (1) is completely in line with the finding of the authors [15] that the perovskites YCo[O.sub.3] and BaCo[O.sub.3] are products of YBa[Co.sub.2][O.sub.6-[delta]] decomposition in air (p[O.sub.2] = 0.21 atm) at temperatures lower than 850[degrees]C.
Buonassisi, "Identifying defect-tolerant semiconductors with high minority-carrier lifetimes: beyond hybrid lead halide perovskites," MRS Communications, vol.