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MINERALS AND SYNTHETIC COMPOUNDS, AmXn, IN WHICH X
ATOMS ARE |
CLOSE PACKED AND A ATOMS OCCUPY OCTAHEDRAL INTERSTICES |
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Perovskite |
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octa |
25% |
fcc |
chain |
6
vertices |
A-
6c, X- 2c/fcc |
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structure |
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In the perovskite
structure 25% of the octahedral voids of each successive layer of |
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FCC packed X atoms are occupied with A atoms.
Also 1/4 of the anion X atoms are |
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substituted for by cations, other than the
species occupying the octahedral voids, |
which have a similar size radius. |
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Ex. CaTiO3 ( calcium titanium
oxide, perovskite ) ( Ti - A ; O, Ca - X ) |
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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. |
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Figure
101 - Perovskite lattice |
click image to enlarge |
structure |
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Polyhedral framework |
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linking surfaces |
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Figure 102 - Perovskite polyhedral |
framework model |
( 88 T, 108 pinges ) |
6
vertices |
click image to enlarge |
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The polyhedral
framework can be modeled as eight AX6 groups coordinated
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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. |
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Cleavage |
Crystal habit |
(100) - imperfect |
cubic |
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Isostructural minerals/compounds |
SrTiO3, SrZrO3, SrHfO3,
SrSnO3, SrFeO3, BaZrO3, BaHfO3,
BaSnO3, BaCeO3, EuTiO3, |
LaMnO3 |
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Page
65 - Structure matters - Perovskite |
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