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ENGR 240 - 9.3.07

ENGR 240 - 9.3.07 - ENGR 240 September 3 2007 Flourite...

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ENGR 240 – September 3, 2007 Flourite Structure (CaF 2 ) o “Ax 2 o remember charge balance o atoms/unit cell 12 o CN 8 Perovskite Structure o “ABO 3 ” type o SrTiO 3 o Corners contain strontium o Faces contain oxygen o Titanium in the center o Atoms/unit cell = 1(Ti) + 1 (Sr 1/8 per corner) + 3 (O ½ per face) Density Calulations for Ceramics o ρ = n’(ΣA c + ΣA A )/V c N A n’ = number of formula units in a unit cell Ex. SrTiO 3 n’ = 1 CaF 2 4 A c atomic weight of cations A A atomic weight of anions V c volume of unit cell N A Avagadros’s Number Layered Silicates o 2D sheet of layered structures Figure 3.14 o Ex. Kaolinite Al 2 (Si 2 O 5 )(OH) 4 o Absorbs liquid Diamond Cubic o Same as Zinc Blende except made of entirely carbon atoms o Common structure for covalently bonded solids C, Si, Ge o FCC + 4 atoms tetrahedral o Atoms/unit cell 8 o CN 4 o Diamond Very hard Strong covalent bonds
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