09-11-Lecture

09-11-Lecture - 1 ENGR 213 Crystal Structures Ceramics...

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Unformatted text preview: 1 ENGR 213 Crystal Structures Ceramics IONIC CERAMIC CRYSTALS more than one element usually different size ions metal + non-metal predominantly ionic bonding cations - give electrons anions - take electrons two characteristics control crystal structure charge balance AX - equal nos. of anions and cations A M X P- M cations and P anions A M B N X P- M & N cations and P anions relative sizes of ions: r CATION / r ANION Ion Size & Structure - 1 How many Aggies to change a tire? Ions arrange to maximise contact with other species Stable arrangements of cations & anions C A Ion Size & Structure - 2 r C / r A and stability affect coord # Coord # and config Linear = 2 Triangular = 3 Tetrahedral = 4 Octahedral = 6 Cubic = 8 LESS COMMON STRUCTURES 3-fold coordination (planar triangle) 0.155 < r C / r A <0.225 2-fold coordination (linear) r C / r A < 0.155 COMMON STRUCTURES - 1 coordination # = 6 atoms touch along CELL edge 0.414 < r C / r A < 0.732 AX structures FCC for A FCC for X Typical of NaCl MgO FeO COMMON STRUCTURES - 2 coordination # = 8 atoms touch along CELL diagonal AX structures Neither A nor X BCC 0.732 < r C / r A <1 Typical of CsCl NaF COMMON STRUCTURES - 3...
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This note was uploaded on 03/26/2008 for the course ENGR 213 taught by Professor Dr.stubbs during the Fall '04 term at Texas A&M.

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09-11-Lecture - 1 ENGR 213 Crystal Structures Ceramics...

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