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

.

  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 ) .
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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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perovskite.gif

 
         Figure 101 -  Perovskite lattice

click image to enlarge

                         structure
   
 
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Polyhedral framework
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linking surfaces

perovskite.gif

 

   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.
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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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