Perovskites CaTiO

Corgne A, Wood B (2003) Trace element partitiorring between silicate melt and Ca-perovskites (CaTiOs and CaSi04)— implications for mantle differentiation. Geophys Res Lett 29(19) 1903, doi 10.1029/2001GL014398... 

Figure 8 The elementary cell of the perovskite CaTiO. (a) Common representation ...

Titanium occurs in nature in the minerals rutile( Ti02), ilmenite (FeTiOs), geikielite, (MgTiOs) perovskite (CaTiOs) and titanite or sphene (CaTiSi04(0,0H,F)). It also is found in many iron ores. Abundance of titanium in the earth s crust is 0.565%. Titanium has been detected in moon rocks and meteorites. Titanium oxide has been detected in the spectra of M-type stars and interstellar space. 

In perovskite (CaTiOs) and its isomorphs such as BaTiC>3, the large alkaline earth ions replace O2- ions in the anion lattice and the Ti4+ ions occupy all the octahedral interstices that are surrounded only by O2- ions, i.e. no Ti4+ ions are immediately adjacent to divalent cations. 

BaTi03 is isostructural with the mineral perovskite (CaTiO ) and so is referred to as a perovskite . The generalized perovskite structure AB03, is visualized as based on a cubic close-packed assembly (see Fig. 2.1) of composition A03 with the A-ion cordinated with 12 oxygen ions and the B-ion in the octahedral interstices (see Fig. 2.39). A consideration of the geometry shows that for a prefect fit the following relationship between the ionic radii holds [12]. 

As has been mentioned, ternary compounds having polyatomic ions such as NO3-, C032-, NFLt+, and so on often have the same types of structures as binary compounds in which a polyatomic ion occupies a lattice site as a unit. The mineral perovskite, CaTiOs, calcium titanate, however, is a somewhat different type of ternary compound that has the structure shown in Figure 3.8(a). Most ternary compounds are oxides, and the general formula ABO3 corresponds to many compounds because A = Ca, Sr, Ba, and so forth, and B = Ti, Zr, Al,... 

The perovskite CaTiOs crystallizes in the space group Pm 3 m. The unit cell contains oxygen atoms at the midpoints of every edge of a cube. There is a calcium atom... 

Barium titanate, which has many novel properties, is a mixed oxide ceramic. It has the same structure as the mineral perovskite, CaTiOs (Fig. 22.13), except, of course, that Ba replaces Ca. Perovskites typically have two metal atoms for every three O atoms, giving them the general formula ABO3, where A stands for a metal atom at the center of the unit cube and B stands for an atom of a different metal at the cube corners. 

Fig. 10.15. Idealized structure of (a) cubic perovskite (CaTiOs) and b) orthorhombic brownmillerite (Ca2Fe20s) lattice with ordered oxygen vacancies ( ) along the cubic [110] direction.

Figure 21.3 Two representations of the structure of perovskite, CaTiOs, showing (a) the octahedral coordination of Ti, and (b) the twelve-fold coordination of Ca by oxygen. Note the relation of (b) to the cubic structure of ReOs (p. 1047).

Fig. 5.23 (a) One representation of a unit cell of perovskite (CaTiOs) (b) the Ca ion is 12-coordinate with respect to the ions. Colour code Ca, purple O, red Ti, pale grey. 

Some high-temperature superconductors adopt a crystal structure similar to that of perovskite (CaTiOs). The unit cell is cubic with a Ti" " ion in each comer, a Ca " ion in the body center, and 0 ions at the midpoint of each edge, (a) Is this unit cell simple, body-centered, or face-centered (b) If the unit cell edge length is 3.84 A, what is the density of perovskite (in g/cm ) ... 

The cubic unit ceU of perovskite, CaTiOs, is drawn in Figure 5.35(c). What are the atomic coordinates of the atoms ... 

Figure 5.35 The cubic unit cells of (a) iridium, (b) CsCl and (c) perovskite (CaTiOs)...

The perovskite (CaTiOs) structure type a double oxide... 

The unit cell of the classical perovskite CaTiOs. The octahedral coordination environment of Site B is indicated. 

Pure primary titanium dioxide does not occur naturally, but is derived by weathering from ilmenite (FeTiOs), perovskite (CaTiOs), and titanite (sphene) (CaTiSiO ). The weathering products form leuxocene ores with up to 68% mtile content. The... 

As an example, we consider oxygen atom 2s functions in the perovskite CaTiOs structure. The oxygen atoms occupy Wyckoff position c of the space group 0 with the site-symmetry 04 The 2s-functions of an oxygen atom transform over Uig irrep of the point group 04. Thus, the induced representation in q basis c,aig) is three-dimensional at each k point (d ) = a4g,np = l,n,q = 3). 

Redfern, S.A.T. (1996) High-temperature structural phase transitions in perovskite (CaTiOs)./. Phys. Condens. Mater., 8, 8267-8285. 

Zhuang, J Tian, Q Lin, S., Yang, W., Chen, L., and Liu, P. (2014) Precursor morphology-controlled formation of perovskites CaTiOs and their photoactivity for As(ni) removal. AppL CataL B Environ., 156-157,108-115. 

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