Second Pauling’s Rule

[freakJoe]

I have problem with those tasks, i was reading about rule, but still have no idea what to do...

 

1) FeTiO3 (mineral Ilmenite) possesses the corundum structure (remember our

discussion in the class) – an hcp array of oxides with cations filling 2/3 of octahedral holes.

Use the bond valence rules (Second Pauling’s Rule) to decide which oxidation states are

present: Fe(II) Ti(IV) or Fe(III) Ti(III).

Bond Distances (dexp, Å) Tabulated reference values Constants

FeO = 3×2.07 and 3×2.20 R0(FeO) = 1.795 Å b = 0.30

TiO = 3×1.88 and 3×2.09 R0(TiO) = 1.815 Å b = 0.37

Check for oxygen valence (what is the coordination number of O?): each oxygen is bound to

Fe and Ti with both bond distances.)

2) CaWO4 has the scheelite structure where the W6+ ions are tetrahedrally

coordinated. Use the bond valence rules (Second Pauling’s Rule) to decide if the WO4

tetrahedra share corners, i.e. oxygens are bridging, or the WO4 tetrahedra are isolated, i.e.

oxygens are terminal. Show your bond strength calculation.