Download presentation

Presentation is loading. Please wait.

Published byDaniel Archer Modified over 2 years ago

1
PX3012 The Solid State Course coordinator: Dr. J. Skakle CM3020 Solid State Chemistry Course coordinator: Dr. J. Feldmann

2
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

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

4
Why Solids? most elements solid at room temperature atoms in ~fixed position simple case - crystalline solid Crystal Structure Why study crystal structures? description of solid comparison with other similar materials - classification correlation with physical properties

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 Kepler wondered why snowflakes have 6 corners, never 5 or 7. By considering the packing of polygons in 2 dimensions, demonstrate why pentagons and heptagons shouldnt occur.

9
Definitions 1. The unit cell The smallest repeat unit of a crystal structure, in 3D, which shows the full symmetry of the structure The unit cell is a box with: 3 sides - a, b, c 3 angles -,,

10
Seven unit cell shapes Cubica=b=c = = =90° Tetragonala=b c = = =90° Orthorhombica b c = = =90° Monoclinica b c = =90°, 90° Triclinica b c 90° Hexagonala=b c = =90°, =120° Rhombohedrala=b=c = = 90° Think about the shapes that these define - look at the models provided.

11
2D example - rocksalt (sodium chloride, NaCl) We define lattice points ; these are points with identical environments

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 The sheets at the end of handout 1 show examples of periodic patterns. On each, mark on a unit cell. [remembering that there are a number of different (correct) answers!]

19
Summary Unit cells must link up - cannot have gaps between adjacent cells All unit cells must be identical Unit cells must show the full symmetry of the structure next section

Similar presentations

© 2016 SlidePlayer.com Inc.

All rights reserved.

Ads by Google