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1、材料科学基础Fundamental of Materials,Prof: Tian Min Bo Tel: 62795426 ，62772851 E-mail: Department of Material Science and EngineeringTsinghua University. Beijing 100084,Lesson nine,3.4 Some Rules Governing the Ionic Compounds,Paulings three rules governing the structure of ionic compounds.1. Anion Coordin
2、ation polyhedron rule Each cation is surrounded by an anion polyhedron, the distance between anion and cation is ror+r-, while the CN depends on r+/r-.,ror+r,ror+r stable ionic compound,ror+r there is some covalent bounding,stable,unstable,2. Valence rule There is a definite relation between valence
3、 and CN. Let S be the strength of electrostatic bonding between a pair of anion and cation,if S1S2S, Then Z (CN)S（CN）（Z+/CN+）,3. The anion polyhedron prefer to share apex instead of sharing edges or faces:,3.5 Crystal Structure of Ceramic Materials,AB AB2 A2B3 ABO3 AB2O4,. AB type 1. NaCl r+/r0.54 o
4、ctahedron CN+6 Z1CN(Z+/CN+)CN1/6 CN6,2. CsCl r+/r0.91 hexahedron CN+8 Z1CN(Z+/CN+)CN1/8 CN8,3. Zinc blende ( ZnS ),CN 4CN+ 4,4. Wurtzite ( ZnS, ZnO ),S(O)1/21/21 2 Zn1/441 2,. AB2 type 1. Fluorspar (CaF2) Li2O Na2O,CN+ 8CN- 4,2. Rutile (TiO2),. A2B3 type ( ),. ABO3 type ( BaTiO3, CaTiO3 ),. AB2O4 type (spinel, MgAl2O4 ),Examples and Discussions,Exercise,Thank you !,9,