Crystalline structure l.

A brief lecture about crystal structure and its properties, types in materials.

1. Crystalline Structure A lecture by Aqeel A. Al- Taie M.Sc. Of Physics September, 2018

2. Outline Classification of Matter Solids: Crystalline and non-crystalline Lattice points Crystal lattice Basis Unit cell Crystal systems Bravais lattice Summary Objectives Define the crystalline structure. Understand the elements of crystal structure. Describe how the structure of crystals is build up. Identify various types of crystal systems and lattices.

3. Classification of Matter Matter Solids Gases Liquids Solids are classified in to two types :  Crystalline .  Non-Crystalline (Amorphous).

4. A crystal or crystalline solid is a solid material, whose constituent atoms, molecules , or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. - Examples: Diamond , Nacl , Kcl , Copper, Silver, and Aluminium . Amorphous (Non-crystalline) Solid is composed of randomly orientated atoms, ions , or molecules that do not form defined patterns or lattice structures. - Examples: amorphous silicon, plastics, and glass.

5. Lattice Points : The points in the space, replacing the atoms in the structure of a crystal , with regular periodic arrangement and have identical environment with respect to other points. . . . . . . . lattice points . . . . . . . . . . . . . .

6. Crystal Lattice : The regular orderly arrangement of lattice points in space which resembles the a toms or molecules in a crystal such that every point has same environment with respect to all other points . * * * * * * * * * * atoms * * * * * * * * * * * * * * * * * * * * Crystal lattice

7. Basis : The set of atoms or molecules attached to each lattice point in a crystal lattice, identical in composition, arrangement and orientation. Crystal Structure = Basis ( * ) + Crystal lattice ( . )

8. Unit Cell : The smallest block or geometrical figure from which the crystal is build up by repetition in three dimensions , ( or) The fundamental grouping of particles which are repeating entities.

9. The unit cell and consequently , the entire lattice , is uniquely determined by the six lattice parameters: a , b , c , α , β and γ . These six parameters are also called as basic lattice parameters.

10. Crystal Systems : On the basis of lattice parameters (a , b, c, α, β and γ) or shape of the unit cell ,crystal systems are classified into 7 categories . No Crystal S tructure Lattice Parameters 1 Cubic a = b = c, α = β = γ = 90° 2 Tetragonal a = b ≠ c, α = β = γ = 90° 3 Orthorhombic a ≠ b ≠ c, α = β = γ = 90° 4 Monoclinic a ≠ b ≠ c, α =β = 90°, γ ≠ 90° 5 Triclinic a ≠ b ≠ c, α ≠ β ≠ γ ≠ 90° 6 Rhombohedral (Trigonal) a = b = c, α = β = γ ≠ 90° 7 Hexagonal a = b ≠ c, α = β = 90°, γ =120°

11. Bravais Lattices In 1950 Bravais showed that , there are fourteen ways of arranging points in space lattice, relating to the seven crystal systems to describe crystals. These fourteen space lattices are called ‘ Bravais lattices ’. Auguste Bravais (1811-1863)

12. Bravais Lattices

13. Summary Crystalline structure is generally present in solids rather than in fluids. There are a crystalline and non-crystalline solids. A crystalline solid is a material in which the basis are arranged in a periodic, 3-D pattern; in oppose from non-crystalline(amorphous) solid. The crystal structure is composed from a crystal lattice and a basis. The smallest component in the crystal is called ‘Unit cell’, and is governed by six lattice parameters; a, b, c, α, β and γ . Due to these parameters, there are 7 crystalline systems. According to the possible arrangement of the lattice points in space lattice, there are 14 types of crystalline lattice, called ‘ Bravais lattices’.

14. THANK YOU