Polymorf - Knowhwere- Perovskite

MINERALS AND SYNTHETIC COMPOUNDS, A_mX_n, IN WHICH X ATOMS ARE

CLOSE PACKED AND A ATOMS OCCUPY OCTAHEDRAL INTERSTICES

Perovskite

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octa	25%	fcc	chain	6 vertices	A- 6c, X- 2c/fcc

structure

In the perovskite structure 25% of the octahedral voids of each successive layer of

FCC packed X atoms are occupied with A atoms. Also 1/4 of the anion X atoms are

substituted for by cations, other than the species occupying the octahedral voids,

which have a similar size radius.

Ex. CaTiO₃ ( calcium titanium oxide, perovskite ) ( Ti - A ; O, Ca - X )

Crystal lattice

The lattice model demonstrates the FCC staggering order of the TiO₆ coordination

groups of atoms in each successive layer. A calcium cation (yellow) is substituted for

each close packed oxygen anion at a vertex in the lattice that is surrounded by three

such AX₆ groups . The polyhedral framework model can be extracted directly from

the lattice as shown.

Polyhedral framework

.
linking surfaces
		Figure 102 - Perovskite polyhedral
		framework model
		( 88 T, 108 pinges )
6 vertices		click image to enlarge
.

The polyhedral framework can be modeled as eight AX₆ groups coordinated

around a central close packed calcium atom (imagined to be located at the center

of the inverted cuboctahedron shown in black). It is also understood that the close

packed oxygen atoms are located at the vertices of the octahedra. The AX₆ groups

are demonstrated to be linked by their vertices into chains parallel to the [100] axis.

Isostructural minerals/compounds

SrTiO₃, SrZrO₃, SrHfO₃, SrSnO₃, SrFeO₃, BaZrO₃, BaHfO₃, BaSnO₃, BaCeO₃, EuTiO₃,

LaMnO₃

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