SOLID STATE PHYSICS

SOLID STATE PHYSICS. By : 12B1 -Ahmed Hany -Ahmed Gamal -Nour El-Deen Metwally Supervisor: Dr/Ahmed Ashour.

What is solid state physics ?. Explains the properties of solid materials. Explains the properties of a collection of atomic nuclei and electrons interacting with electrostatic forces. Formulates fundamental laws that govern the behavior of solids..

Crystalline Solids. Crystalline materials are solids with an atomic structure based on a regular repeated pattern. The majority of all solids are crystalline. More progress has been made in understanding the behavior of crystalline solids than that of non-crystalline materials since the calculation s are easier in crystalline materials..

crys_not_crys. 4. + - + - + - + - + - + - + -.

5. SINGLE CRYSTALS. Diagram showing the range of translational periodicity in materials.

6. CRYSTAL LATTICE. What is a crystal lattice? In crystallography, only the geometrical properties of the crystal are of interest, therefore one replaces each atom by a geometrical point located at the equilibrium position of that atom..

7. An infinite array of points in space, Each point has identical surroundings to all others. Arrays are arranged in a periodic manner..

8. Crystal Structure. Crystal structures can be obtained by attaching atoms, groups of atoms or molecules which are called basis (motif) to the lattice sides of the lattice point..

A two-dimensional Bravais lattice with different choices for the basis.

10. Five Bravais Lattices in 2D.

S. S. 11. 2D-Crystal. S. Unit Cell. S. Unit Cell in 2D.

12. The unit cell and, consequently, the entire lattice, is uniquely determined by the six lattice constants : a, b, c, α, β and γ ..

13. Three common Unit Cell s in 3D. qqno peaaJLJ00-ooe; aqno pejowoo-/poq aqno Oldugs.

14. Simple Cubic (SC) Body-Centered Cubic (BCC) Face-Centered crystal (FCC) Hexagonal Close Packing (HCP).

Simple Cubic (SC):. The simple cubic (SC) unit cell can be imagined as a cube with an atom on each corner. This unit cell is the simplest for people to understand, although it rarely occurs in nature due to its low packing. SC has 1 atom per unit cell and atomic packing factor APF = 52%. Example: NaCl structure..

Simple Cubic structure.

Body-Centered Cubic (BCC). The Body-Centered Cubic (BCC) unit cell can be imagined as a cube with an atom on each corner, and an atom in the cube’s center. It is one of the most common structures for metals. BCC has 2 atoms per unit cell and Atomic Packing Factor APF = 68%. Example: Iron.

Body-Centered Cubic (BCC).

Face-Centered Crystal (FCC). The Face-Centered Crystal (FCC) unit cell can be imagined as a cube with an atom on each corner, and an atom on each face. It is one of the most common structures for metals. FCC has 4 atoms per unit cell and Atomic Packing Factor APF = 74%. Example: Steel Iron..

Face-Centered Crystal (FCC).

Hexagonal Close Packing. The Hexagonal Close-Packed (HCP) unit cell can be imagined as a hexagonal prism with an atom on each vertex, and 3 atoms in the center. It can also be imagined as stacking 3 close-packed hexagonal layers such that the top layer and bottom layer line up. HCP is one of the most common structures for metals. HCP has 6 atoms per unit cell and Atomic Packing Factor APF = 74%. Example: Zinc.

Hexagonal Close-Packed.

Types of Bonding Ionic Bonding Van Der Waals Bonding Metallic Bonding Covalent Bonding Hydrogen Bonding High Melting Point Hard and Brittle Non conducting solid NaCl, CsCl, ZnS Low Melting Points Soft and Brittle Non-Conducting Ne, Ar, Kr and Xe Variable Melting Point Variable Hardness Conducting Fe, Cu, Ag Very High Melting Point Very Hard Usually not Conducting Diamond, Graphite Low Melting Points Soft and Brittle Usually Non-Conducting İce, organic solids.

Coulomb force. It is useful to analyze the interaction between two objects say, between two atoms or molecules with the use of a potential energy diagram, which is a plot of the potential energy versus the separation distance. For the simple case of two point charges, and the potential energy PE is given by: Where r is the distance between the charges, and the constant k is equal to 9 x 10 9 N.m 2 /C 2 If the two charges have the same sign, the potential energy PE is positive for all values of r.

Sources of VDW Forces. Dipole-dipole.(2 polar) 2. Dipole-induced dipole ( HCl + Ar ) 3. Dispersion (London dispersal effect) 2 non-polar.

Dipole-Dipole ( Keesom Effect). Two polar molecules align so that + and - are matched (electrostatic attraction)..

Phonons. Consider the regular lattice of atoms in a uniform solid material . There should be energy associated with the vibrations of these atoms. But they are tied together with bonds, so they can't vibrate independently. The vibrations take the form of collective modes which propagate through the material. Such propagating lattice vibrations can be considered to be sound waves. And their propagation speed is the speed of sound in the material..

The vibrational energies of molecules are quantized and treated as quantum harmonic oscillators . Quantum harmonic oscillators have equally spaced energy levels with separation Δ E = h  . So the oscillators can accept or lose energy only in discrete units of energy h  . The evidence on the behaviour of vibrational energy in periodic solids is that the collective vibrational modes can accept energy only in discrete amounts, and these quanta of energy have been labelled "phonons"..

PHONONS. Quanta of lattice vibrations. Energies of phonons are quantized.

Phonon-phonon collisions. The coupling of normal modes by the unharmonic terms in the interatomic forces can be pictured as collisions between the phonons associated with the modes. A typical collision process of.

Energy Bands. Energy band theory states that there are 2 energy bands with a gap between them: Valence band : The valence band is the band of electron orbitals that electrons can jump out of, moving into the conduction band when excited. The valence band is simply the outermost electron orbital of an atom of any specific material that electrons actually occupy. This is closely related to the idea of the valence electron. 2) Conduction band : The conduction band is the band of electron orbitals that electrons can bounce up into from the valence band when energized. At the point when the electrons are in these orbitals, they have enough energy to move freely in the material. This movement of electrons makes an electric current flow. 3) Forbidden energy gap : The gap between the valence band and the conduction band is referred to as forbidden gap. As the name suggests, the forbidden gap doesn’t have any energy and no electrons stay in this band. If the forbidden energy gap is greater, then the valence band electrons are tightly bound or firmly attached to the nucleus. We require some amount of external energy that is equal to the forbidden energy gap..

Questions. 1. Which one of the following process is used to purify a soluble solid? A. Evaporation B. Crystallisation C. Condensation D. Distillation.

2. Crystals having low melting points are in A. Vander waal's bond B. lonic bond C. Covalent bond D. Metallic bond . 3. The working of a quartz crystal in the watch is based on the A. photo electric effect B. Johnson effect C. Piezo -electric effect D. Edison effect.

4. When electrons are trapped in the crystal lattice in place of anion vacancy, the defect in the crystal is known as A. Non- stochiometric defect. B. F-centre C. stochiometric defect D. Frenkel defect 5. Which one of the following properties of a liquid does not affect its rate of evaporation? A. Volume B. surface area C. temperature D. boiling point.