1 / 27

Lecture 2.1

Lecture 2.1. Crystalline Solids. Crystalline Solids. Poly-crystalline solids - Grains Mono-crystalline solids- Whiskers, Wafers. Crystal Lattices. Crystal Systems =>14 Bravais Lattices. Bravais lattice (abc). Lattice is constructed of repeated unit cells Lattice Point - 1/3a,1/2b,1/4c

nelia
Download Presentation

Lecture 2.1

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 2.1 Crystalline Solids

  2. Crystalline Solids • Poly-crystalline solids - Grains • Mono-crystalline solids- Whiskers, Wafers

  3. Crystal Lattices

  4. Crystal Systems =>14 Bravais Lattices

  5. Bravais lattice (abc) • Lattice is constructed of repeated unit cells • Lattice Point - 1/3a,1/2b,1/4c • Crystallographic Direction (vector from 0,0,0 to xyz) which is defined by • [uvw] smallest set of integers having the same ratio as xyz • bar over number = minus number

  6. Close Packed Structures • Cubic, BCC, FCC, HCC are the focus of this course • Determining distances and volume fractions in Cubic Structures

  7. Miller indices for a plane (hkl) Family of Miller Planes {hkl}

  8. EXAMPLE- Miller Index • intercepts on a,b&c axes=3,1&2, respectively • reciprocals = 1/3,1/1&1/2, respectively • smallest set of integers with same common ratio = 2,6&3 • Miller indexes of Plane, (hkl)=(263) • also called “reciprocal space plane”

  9. Family of Planes {110}

  10. Measuring Structure with X-rays • Generate X-ray radiation • X-ray Diffraction (=90) • ao= cubic lattice parameter

  11. X-Ray Generation • Electron Scattering • Broad Band X-rays • Electron Kickout • K,L,M shell electron • Replace with higher electron • Transition gives X-rays • one wave length • K,K, L, L K K

  12. X-ray GenerationEnergy Level Diagrams -0.85 eV 4 -1.51 eV 3 L L K L -3.40 eV 2 K K -13.6 eV 1

  13. X-ray Camera-1 • Single Crystal Camera • Broad Band X-rays • all  in source • only Bragg (diffracting) wavelengths reflect

  14. SiGe Crystal

  15. X-ray Camera-2 (film strip) • X-rays of Single  • All (hkl) planes are exposed at all angles at all times • Diffraction of Bragg planes

  16. Electron Diffraction Focused Electrons • Electrons of different energy • Transmission through sample • CCD detector Thinned Sample CCD Detector

  17. Seeing Crystal Structure with and Atomic Force Microscope • Electron Microscope • Atomic Force Microscope • Scanning Tunneling Microscope

  18. Diffracting Planes

  19. Changing Crystal Structure – Allotropic Phase Change HCP->FCC->BCC->SC • Ca(fcc) --(447ºC)-> Ca(bcc) • Co(hcp) --(427ºC)--> Co(fcc) • Fe(bcc) --(912ºC)-->Fe(fcc) --(1394ºC)-->Fe(hcp) • Na(bcc) --(-233ºC)--> Na(hcp) • Ti(hcp) --(883ºC)-->Ti(bcc) • Zr(hcp) --(872ºC)--> Zr(bcc) Decreasing density with increasing temperature!

  20. Defects in Crystal Structure • Vacancy, Interstitial, Impurity • Schottky Defect • Frenkel Defect • Dislocations – edge dislocation, line, screw • Grain Boundary

  21. Effect of Structure on Mechanical Properties • Elasticity • Plastic Deformation

More Related