2. Structure of solids

Introduction

• Amorphous Vs Crystalline

• Amorphous:
• Definition: Non-crystalline materials lacking long-range order.
• Characteristics:
• Short-range order with atoms not arranged in a specific pattern.
• Lack of clear structure.
• Examples: Glass, plastic, resin.
• Crystalline:
• Definition: Materials with highly ordered structures at the molecular and atomic levels.
• Characteristics:
• Long-range order with molecules and atoms arranged in a specific pattern.
• Exhibits distinct crystal lattice structure.
• Types:
• Monocrystalline: Consists of a single crystal.
• Polycrystalline: Comprises multiple randomly oriented crystals.
• Properties:
• Anisotropic: Different properties in different directions.
• Regular and repeating arrangement of atoms.
• Examples: Minerals, metals, semiconductors.
• Liquid Crystalline Materials:

• Definition: Materials exhibiting properties of both liquids and crystals.
• Characteristics:
• Anisotropic: Atoms or molecules have different properties in different directions.
• Atoms are mobile but can form a lattice structure similar to crystals.
• Molecules are easily polarizable.
• Examples: Liquid crystals, such as those used in liquid crystal displays (LCDs) and certain polymers.
• Mechanical deformations
• Mechanical deformation refers to the change in the shape or size of an object due to applied forces. This deformation can be temporary or permanent, depending on the material and the forces involved.

• Types of Deformation:
• Elastic Deformation: As you mentioned, elastic deformation is reversible. When the applied force is removed, the material returns to its original shape. This is like stretching a rubber band - it stretches under tension but snaps back to its original size when you let go.
• Plastic Deformation: In contrast, plastic deformation is permanent. The material does not return to its original shape after the force is removed. Bending a paperclip is an example - it retains its new bent shape.
• Hooke's law.
• Hooke's Law:
• Definition: Hooke's Law states that the stress applied to a material is directly proportional to the relative strain induced in the material.
• Young's Modulus (E):
• Definition: Young's modulus is a coefficient of proportionality that relates stress to strain in a material.
• Relative Deformation (ε):
• Definition: Relative deformation is the ratio of change in length (∆L) to the original length (L₀) of the material.

• Strength and Hardness of Materials:
• Strength:
• Definition: Strength refers to the ability of a material to withstand applied stress without failure.
• Types of Strength:
• 1. Proportional Limit:Stress is directly proportional to strain, indicating elastic behavior.
• 2. Elastic Limit: The material is able to return to its original shape after the applied stress is removed.