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What are dislocations? Recap of 3.14/3.40 Lecture on 9/27/2012 Sangtae Kim Oct/2/2012.

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Presentation on theme: "What are dislocations? Recap of 3.14/3.40 Lecture on 9/27/2012 Sangtae Kim Oct/2/2012."— Presentation transcript:

1 What are dislocations? Recap of 3.14/3.40 Lecture on 9/27/2012 Sangtae Kim Oct/2/2012

2 What are dislocations? Why are they important? How do they move in the crystal? A research topic related to dislocations Contents

3 What are dislocations? 1D Line defects, in which crystal registry is lost A machine to cut bonds on one plane, and then re- stitch them together, one by one – Dislocation Glide Carry local deformation and stress Edge, screw, mixed dislocations

4 Edge dislocation Simple cubic illustration Illustration with bonds Local environment is different only at the core. Localized shear b perpendicular to line direction

5 Edge dislocation Simple cubic illustration Illustration with bonds Local environment is different only at the core. Localized shear b perpendicular to line direction

6 Screw dislocation view from top

7 Screw dislocation view from top b parallel to line direction

8 Screw dislocation

9 Fantastic!

10 In reality Mixed dislocations – b at some angle to the line direction. -- e.g. dislocation loops from the Frank Reed source

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12 Why are they important? It controls the yield strength and subsequent plastic deformation at ordinary temperature. Electric defects in semiconductors and optical materials – they are undesirable there. We can understand 2D defects as a set of 1D defects

13 How do they move? Glide - slip plans Climb - 1D defects: vacancy, interstitials In reality, there are bits of both + entanglement

14 Glide Motion

15

16 Slip

17 Climb Collective vacancy motion/interstitials required. So to harden a material, we want more climb, instead of glide to harden a material.

18 Hardening Mechanism

19 A Research Question LiCoO2: typical battery cathode material Li removal with no structural change Transition Metal Alkali Metal (Na or Li)

20 A Research Question Iso-structural NaCoO2 shows change.

21 O3 – P3 transformation A A B B C B A C B C C A A A B B O3 LayeredP3 Layered Na TM

22 O3 – P3 transformation A A B B C B A C B C C A A A B B O3 LayeredP3 Layered Na TM

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24 Sangtae Kim,

25 Edge dislocation Simple cubic illustration

26 Edge dislocation Simple cubic illustration


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