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
Lesson seven
§ 2.9 Some Additional Terminology
in Crystallography
? Ⅰ,Single crystal versus polycrystal
1,For single crystals there is only one type of structure with
same orientation.
Single crystals is characterized by anisotropy.
2,Polycrystal consists of a lot of grain,small single crystals,
with same structure but different orientations,These small
single crystals are called grains,The boundaries between
them are called grain boundaries,
single crystal polycrystal
grain
grain
boundary
? Ⅱ,Allotropy
Same crystal has different crystallographic
structure at different condition.
Examples,C,graphite,diamond,CNT
L i q u i dC1 5 4 0FeC1 4 0 0FeC910Fe ?????? ???
BCC BCCFCC
? Graphite
? C60 molecule
? Carbon Nanotubes
? Ⅲ,Atomic radii
Definition:
2
ABSr ?
Examples and Discussions
Exercise
Thank you !
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