PH2002 Physics of Materials Notes

Course Overview

• Instructor: Dr. Y. Ashok Kumar Reddy, Assistant Professor of Physics

• Contact Information: akreddy@iiitdm.ac.in, Office: 119-K (North-East) H25

• Class Schedule:

  • Tuesday: 11:00-11:50 AM

  • Wednesday: 8:00-8:50 AM

  • Thursday: 1:00-1:50 PM

  • Friday: 9:00-9:50 AM

Course Content

Physics of Materials

• Key Topics:

  • Atoms in crystals

  • Atomic bonding

  • Free electron theory

  • Band theory

  • Fermi level

  • Energy bands

  • Conductors, Insulators, Semiconductors, Superconductors

  • Dielectrics, Magnetic materials, Plasmonic materials

Recommended Textbooks:

1. Arthur Beiser; Shobhit Mahajan; S. Rai Choudhury - Concepts of Modern Physics, 7th Edition

2. Charles P. Poole, Jr.; Frank J. Owens - Introduction to Nanotechnology

3. Robert L. Jaffe; Washington Taylor - The Physics of Energy

Marks Distribution

• Mid-Semester: 25 Marks

• Project (Assignments & Tutorials): 25 Marks

• End-Semester: 50 Marks

• Total: 100 Marks

  • Tentative Dates:

    • Mid-semester: February 25th

    • Compilation of Attendance: April 22nd

    • End-semester: April 28th

Learning Objectives

• Understand various states of materials and their properties.

• Explore nanotechnology and energy resources for engineering applications.

Learning Outcomes

• Apply physics concepts to materials and their applications.

• Evaluate and select suitable materials for energy, medical, and industrial applications.

Fundamentals of Atomic Structure

Basics of Atoms

• Matter is made of atoms, which consist of:

  • Protons: Positively charged.

  • Neutrons: No charge.

  • Electrons: Negatively charged.

• Atoms form the basic building blocks for solids, liquids, gases, and plasmas

Binomial Models of Atoms

1. Thomson Model: Plum-pudding model, suggesting a uniform positive charge with electrons embedded.

2. Bohr Model: Electrons orbit the nucleus in fixed paths, energy quantization.

   • Stability requires balancing forces: centrifugal vs centripetal.

3. Wilson-Sommerfeld Model: Allows for elliptical electron orbits.

Atoms in Crystals

• Crystalline solids have atoms arranged in a defined, ordered structure.

• Key Terms:

  • Lattice: Periodic structure of points in space.

  • Basis: Group of atoms associated with lattice points.

Types of Crystal Structures

Crystalline vs Amorphous Solids

• Crystalline: Atoms have long-range order (e.g., Iron, Copper).

• Amorphous: Atoms arranged randomly (e.g., Glass).

Unit Cell

• Defined as the smallest repeating unit in a crystal structure.

• Lattice points are located at corners, faces, or center depending on the unit cell type.

Crystal Systems

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. Rhombohedral: a=b=c, α=β=γ≠90°.

5. Hexagonal: a=b≠c, α=β=90°, γ=120°.

6. Monoclinic: a≠b≠c, α=γ=90°, β≠90°.

7. Triclinic: a≠b≠c, α≠β≠γ.

Atomic Bonding

Overview of Bonding Types

• Primary Bonding: Involves chemical bonds (ionic, covalent, metallic).

• Secondary Bonding: Weaker physical forces (e.g., Van der Waals forces).

Ionic Bonding

• Formed through electrostatic attraction between charged ions.

• Strong bond energy between 600-1500 kJ/mole.

Covalent Bonding

• Involves sharing of electrons between atoms; can be strong or weak based on atomic makeup.

• Found in materials like diamond, silicon.

Metallic Bonding

• Found in metals, characterized by a sea of free electrons which contribute to conductivity and malleability.

Summary of Bonding Types

• Ionic, covalent, and metallic are primary bonds that define the properties of materials.

• Secondary bonds are weaker, important in gases and liquids.

Free Electron Theory

Overview

• Explains electrical and thermal properties of metals.

Important Concepts

• Drift Velocity: Average velocity of free electrons under an electric field.

• Relaxation Time (τ_r): Time taken for electrons to return to equilibrium after disruption.

• Mean Free Path (λ): Average distance traveled by electrons between collisions.

Limitations of Classical Free Electron Theory

• Cannot explain phenomena like the photoelectric effect or electrical conduction in semiconductors.

Quantum Free Electron Theory

• An extension of classical theory incorporating quantum mechanics.

Energy Bands

Understanding Band Structure

• Valence Band: Occupied by valence electrons.

• Conduction Band: Unfilled energy states just above the valence band.

• Forbidden Gap: Energy gap between the valence band and conduction band.

  • Metals: Overlap of valence and conduction bands.

  • Semiconductors: Small forbidden gap allows for charge carrier generation under thermal excitation.

  • Insulators: Large forbidden gap prevents electron movement.

Fermi Energy

• Represents the highest occupied energy level at absolute zero temperature.

• Influences electrical and thermal properties of materials.

Conductors, Insulators, and Semiconductors

Conductors

• Materials allowing easy flow of electric current (e.g., Copper, Silver).

• Characterized by free-moving outer electrons that facilitate conductivity.

Insulators

• Materials that inhibit electron movement (e.g., Glass, Wood).

• Excellent insulation arises from tightly bound outer electrons.

Semiconductors

• Can behave as conductors or insulators based on conditions (e.g., Silicon, Germanium).

• Intrinsic Semiconductors: Pure form without added impurities.

• Extrinsic Semiconductors: Doped with impurities to create majority charge carriers.

  • n-type: Doped with pentavalent impurities.

  • p-type: Doped with trivalent impurities.

Superconductors

Characteristics

• Lose electrical resistance below a critical temperature (Tc).

• Exhibit the Meissner effect, repelling magnetic fields.

• Applications include Maglev trains, sensitive magnetometers, and MRI machines.

Types of Superconductors

• Type-I: Show complete expulsion of magnetic fields.

• Type-II: Allow partial penetration of magnetic field.

Applications

• Magnetic levitation, electronics, medical technology, and advanced scientific instruments.