材料科学基础-课件 清华skja_10

§3.8 Electron Phases (Hume-Rothery phases)
Feature: ⑴ Identical on similar structure occur at approximately the same electron concentration, e/a.
For example: CuZn : β Cu5Zn8 : γ CuZn3 : ε(HCP) β: (2+1)/2 = 21/14 γ: 21/13 ε: 21/12
材料科学基础
Fundamental of Materials
Prof: Tian Min Bo
Tel: 62795426 ，62772851 E-mail: tmb@mail.tsinghua.edu.cn Department of Material Science and Engineering Tsinghua University. Beijing 100084

Ⅱ. Three principles for the structure
1. space-filling principle: Atoms tend to fill the space as closely as possible
2. Symmetry principle: Atoms tend to build a configuration of high symmetry
for Cu : for Mg :
CN 6(Cu Mg ) 6(Cu Cu) 12 CN 4(Mg Mg ) 12(Mg Cu) 16
2. phase A B Cr Mo W V Mn Fe Co Ni
electrons atom 7
3. Topologically close-packed phase
2. Diamond, Zinc blende, Wurtzite types Zinc blende: (Be Zn (Al Wurtzite: (Zn Cd (Cd
Ca Hg)(S Se Te) Ga In)(P As Sb) Mn)S Mn)Se
3. NiAs structure
Example: (Cr Fe Co Ni)(S Se Sb) (Fe Co)Te (Mn Fe Ni Pt Cn)Sn Ni(As Sb Bi)
Lesson ten
§3.6 Intermetallic Compounds (Intermetallic Phases)

Ⅰ. Future
1. The structure of AmBn differs from those of either A or B 2. Its composition is variable to more or less extension 3. Mixed bonding 4. Intermediate properties
3. Principle of multi-dimensional connection

Ⅲ. Intermetallic compounds
2 a 4d B
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Examples: 1. Laves phases MgCu2
MgZn2
MgNi2
rB
2 8
a
A原子
B原子
rA rB

3 2
1.225
2. Complex structure
rB rA 0.59
M3C , (Fe3C) , M23C6 , M6C properties of interstitial compounds
⑴ Some metallic properties
⑵ Hard and brittle
⑶ For size factor compounds
Condition A >> B B: H (0.46), B (0.97), C (0.77), N (0.71)
1. Simple interstitial compound structure
rB rA
0.59
A: Transition metals
B: Interstitial elements (H, B, C, N)
Structure
• Normal state —— Ni : As = 1 : 1
3
1 4 c
c
4
• When Ni does not full fill octahedral interspaces
Ni : As < 1 : 1
• Extreme state： Ni occupy trigonal interspaces

Ⅱ. Classification
according to structure 1. NaCl and CaF2 types NaCl:
(Mg Ca Sr Ba)(Se Te) (Mn Pb Sn)(Se Te)
CaF2:
PtSn2 PtIn2 Pt2P
Anti-CaF2: Mg2(Si Ge Sn Pb) Cu2Se Li3AlN2 LiMg(N As Sb Bi) AgMgAs
Examples and Discussions
Exercise
Thank you !
10
§3.7 Normal Valence Compounds
Ⅰ. Definition:
If the number of valence electrons of the cation is sufficient to complete octahedron of the anion, the compound is called the normal valence compounds. CmAn meC＝n(8－eA) sometimes: m(eC－eCC)＝n(8－eA－eAA) Example:
⑵ Components IB or transition metal＋metals in B group ⑶ Composition range is related to e/a
⑷ Metallic character
§3.9 Size Factor Compounds

Ⅰ. Interstitial phases (Interstitial compounds)
Ni : As > 1 : 1
4. Electron Phase
(Electron compounds)
For Alloys of IB or transition metals, and B group metals phases with sane or similar structure occur at approximately some electron concentration(e/a) these alloys are therefore called as electron compounds

Ⅱ. Formation
A→←B The property of AmBn is between that of A and B.

Ⅲ. Factor governing the structure of “compounds”.
1) Electrochemical factor (X) 2) Electron concentration (e/a) 3) Size factor Metal Nonmetal Metalloid