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PX3012 The Solid State Course coordinator: Dr. J. Skakle

SOLID STATE. Crystals. Crystal structure basics unit cells symmetry lattices. Some important crystal structures and properties close packed structures octahedral and tetrahedral holes basic structures ferroelectricity. Diffraction how and why - derivation. Objectives.

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PX3012 The Solid State Course coordinator: Dr. J. Skakle

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    1. PX3012 The Solid State Course coordinator: Dr. J. Skakle

    2. SOLID STATE Crystals

    3. Objectives By the end of this section you should: be able to identify a unit cell in a symmetrical pattern know that there are 7 possible unit cell shapes be able to define cubic, tetragonal, orthorhombic and hexagonal unit cell shapes

    5. Crystals are everywhere!

    6. More crystals

    7. Early ideas Crystals are solid - but solids are not necessarily crystalline Crystals have symmetry (Kepler) and long range order Spheres and small shapes can be packed to produces regular shapes (Hooke, Hauy)

    8. Group discussion

    9. Definitions 1. The unit cell The smallest repeat unit of a crystal structure, in 3D, which shows the full symmetry of the structure

    10. ? Seven unit cell shapes Cubic a=b=c ?=?=?=90 Tetragonal a=b?c ?=?=?=90 Orthorhombic a?b?c ?=?=?=90 Monoclinic a?b?c ?=?=90, ? ? 90 Triclinic a?b?c ? ?? ?? ? 90 Hexagonal a=b?c ?=?=90, ?=120 Rhombohedral a=b=c ?=?=??90 Think about the shapes that these define - look at the models provided.

    11. 2D example - rocksalt (sodium chloride, NaCl)

    12. Choice of origin is arbitrary - lattice points need not be atoms - but unit cell size should always be the same.

    13. This is also a unit cell - it doesnt matter if you start from Na or Cl

    14. - or if you dont start from an atom

    15. This is NOT a unit cell even though they are all the same - empty space is not allowed!

    16. In 2D, this IS a unit cell In 3D, it is NOT

    17. All M.C. Escher works (c) Cordon Art-Baarn-the Netherlands. All rights reserved.

    18. Examples

    19. Summary

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