# None - Crystal Structure Ashraf Bastawros...

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Material Sciences and Engineering, Material Sciences and Engineering MatE271 1 Crystal Structure Ashraf Bastawros www.public.iastate.edu\~bastaw\courses\Mate271.html Week 2 Material Sciences and Engineering MatE271 Week 2 2 - Define basic terms in crystallography - Be able to identify 7 crystal systems and 14 Bravais lattices - To compare and contrast the structures of metal, ceramics and polymer materials - Explain the three most important structures for metals - Calculate atomic structure densities Goals for this unit

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Material Sciences and Engineering, Material Sciences and Engineering MatE271 Week 2 3 Crystal Structure and Periodicity Crystalline Materials atoms are in an ordered 3-D periodic array Single crystal or polycrystalline solids ( metals, ceramics, semiconductors, some polymers ) Amorphous Materials short range order ( glasses, many polymers ) Intermediates Material Sciences and Engineering MatE271 Week 2 4 Crystal Structure and Periodicity Lattice - a 3-D array of positions in space. A geometric framework on which to hang atoms Unit Cell - the smallest repeat unit which defines the crystal structure 2-D 3-D 2-D Note - In these cases, there is one atom centered on each lattice site
Material Sciences and Engineering, Material Sciences and Engineering MatE271 Week 2 5 Simple Cubic (SC) Lattice Crystal Structure Hang 1 atom on each lattice point SC lattice and crystal structure a = 2R Where: R = atomic radius atom a = lattice parameter Material Sciences and Engineering MatE271 Week 2 6 Axes Labels Lattice constant - a, b and c are lengths of edges - α , β , γ are angles ( α is across from a, etc.) a b c α β γ By convention origin - 0,0,0 z y x

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Material Sciences and Engineering, Material Sciences and Engineering MatE271 Week 2 7 Crystal Systems ( 7-systems ) Tetragonal a=b c α=β=γ=90 Cubic a=b=c α=β=γ=90 Orthorhombic a b c
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## This note was uploaded on 12/03/2010 for the course ENG ENG3365 taught by Professor Zayed during the Spring '10 term at University of South Florida.

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None - Crystal Structure Ashraf Bastawros...

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