Lecture11 twins-defects-creep
- 1. Twins and Defects
- 2. Twinning A twin is a symmetrical intergrowth of two or more crystals of the same substance Twinning can be considered a type of planar defect The surface on which two individuals are united is known as the composition surface. If this surface is a plane, it is called the composition plane and can be irregular or regular
- 3. Twinning The operations that relate a crystal to its twinned counterpart are symmetry operations: ‣ twin plane - reflection by a mirror plane ‣ twin axis - rotation about a crystal direction common to both, with the angular rotation normally 180° ‣ twin center - inversion about a point
- 4. Twin Classification 4 types of twins: ✦ Contact ✦ Polysynthetic ✦ Penetration ✦ Cyclic
- 5. Contact & Penetration Contact twins have a regular composition surface separating the two individuals; the twin is defined by a twin plane Penetration twins are made up of interpenetrating individuals having an irregular composition surface, and the twin law is usually defined by a twin axis direction
- 6. Polysynthetic & Cyclic Multiple twins that have three or more individual crystals twinned according to the same law and if all the composition surfaces are parallel, the resulting group is a polysynthetic twin If successive composition planes are not parallel, a cyclic twin results
- 7. Common Twins Swallowtail Polysynthethic Penetration Twin Gypsum Albite Twin Twin Galena
- 8. Common Twins Penetration Penetration Carlsbad Twin Twin Pyrite Twins Orthoclase Staurolite
- 11. Causes of Twinning Growth twins - error in stacking of unit cells when crystal first start to grow Transformation twin - variations in temperature and pressure stresses the lattice - lattice relieves the stress by “warping” Deformation twin - some kind of stress is put on the crystal structure - crystal relieves stress by twinning
- 12. Structural Defects As a crystal grows, structural defects are incorporated into the mineral Such imperfections affect growth rate, crystal morphology, and basic properties of crystalline materials, such as strength, conductivity, mechanical deformation, and color
- 13. Structural Defects 3 Types: point line plane
- 14. Point Defects
- 15. Frenkel & Shottky Defects Frenkel Shottky
- 16. Line Defects Edge Screw
- 17. Edge Dislocation
- 19. Planar Defects Grain Boundaries Twin Planes Sub-grain Boundaries
- 20. Grain Boundaries
- 21. Twin Planes
- 24. Crystal Deformation Dislocation Slip
- 25. Migration of Vacancies thru Crystal Lattice
- 26. Dislocations Quartz Transmission Electron Microscope Photos
- 27. Dislocations Quartz Transmission Electron Microscope Photos
- 28. Dislocations Quartz Strain-free Neoblasts
- 30. Order-Disorder