Polymorf - Knowhwere- ReO3

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

CLOSE PACKED AND A ATOMS OCCUPY OCTAHEDRAL INTERSTICES

ReO₃

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

structure

The ReO₃ structure is identical to perovskite except that there is only one species

of FCC packed X atoms. Also 1/4 of these anions are eliminated instead of being

substituted for. This leaves large unoccupied cuboctahedral shaped voids in the

structure with eight AX₆ groups coordinated around each. As with perovskite 25% of

the octahedral voids are occupied and the occupied AX₆ groups form vertex linked

chains parallel to the [100] axis.

Ex. ReO₃ ( Re - A , O - X )

Crystal lattice

Modeled the same as perovskite except that triangles are removed from the

regions of the lattice where the cuboctahedral voids are located (in the centers of

the eight AX₆ groups coordinated around them).

Polyhedral framework

The polyhedral framework model is similar to perovskite except that squares

are used to brace the octahedra to indicate there is a cuboctahedral void in the

center.

Isostructural minerals/compounds

MoF₃, NbF₃, TaF₃, WO₃ (high temperature)

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Page 66 - Structure matters - ReO₃