K.Pradeep

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CRYSTAL STRUCTURES K.PRADEEP CHAND Asst. Professor School of Mechanical Engineering Vignan University. School of Mechanical Engineering Vignan University

CLASSIFICATION OF MATTER : 

CLASSIFICATION OF MATTER School of Mechanical Engineering Vignan University

SOLIDS : 

SOLIDS Solids are again classified in to two types Crystalline Non-Crystalline (Amorphous) School of Mechanical Engineering Vignan University

What is a Crystalline solid? : 

What is a Crystalline solid? 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. So a crystal is characterized by regular arrangement of atoms or molecules. School of Mechanical Engineering Vignan University

Examples ! : 

Examples ! Non-Metallic crystals: Ice, Carbon, Diamond, Nacl etc… Metallic Crystals: Copper, Silver, Aluminium, Tungsten, Magnesium etc… School of Mechanical Engineering Vignan University

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Crystal = Lattice + Motif Motif or basis: an atom or a group of atoms associated with each lattice point. Space Lattice : An array of points such that every point has identical surroundings. Or Translationally periodic arrangement of points in space is called a lattice. School of Mechanical Engineering Vignan University

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A 2D lattice School of Mechanical Engineering Vignan University

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+  Lattice Motif School of Mechanical Engineering Vignan University

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                                                        Crystal = School of Mechanical Engineering Vignan University

CRYSTALLINE SOLID : 

CRYSTALLINE SOLID School of Mechanical Engineering Vignan University

SINGLE CRYSTAL : 

SINGLE CRYSTAL Single Crystal example School of Mechanical Engineering Vignan University

AMORPHOUS SOLID : 

AMORPHOUS SOLID Amorphous (Non-crystalline) Solid is composed of randomly orientated atoms , ions, or molecules that do not form defined patterns or lattice structures. Examples to amorphous materials include amorphous silicon, plastics, and glasses. Amorphous silicon can be used in solar cells and thin film transistors. School of Mechanical Engineering Vignan University

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Non-crystalline School of Mechanical Engineering Vignan University

UNIT CELL : 

UNIT CELL The smallest component of the crystal (group of atoms, ions or molecules), which when stacked together with pure translational repetition reproduces the whole crystal. School of Mechanical Engineering Vignan University

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The unit cell and, consequently, the entire lattice, is uniquely determined by the six lattice constants: a, b, c, α, β and γ. These six parameters are also called as basic lattice parameters. School of Mechanical Engineering Vignan University

PRIMITIVE CELL : 

PRIMITIVE CELL The unit cell formed by the primitives a, b and c is called primitive cell. A primitive cell will have only one lattice point. If there are two are more lattice points it is not considered as a primitive cell. As most of the unit cells of various crystal lattice contains two are more lattice points, its not necessary that every unit cell is primitive. School of Mechanical Engineering Vignan University

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Primitivecell Primitivecell Nonprimitive cell School of Mechanical Engineering Vignan University

CRYSTAL SYSTEMS : 

CRYSTAL SYSTEMS We know that a three dimensional space lattice is generated by repeated translation of three non-coplanar vectors a, b, c. Based on the lattice parameters we can have 7 popular crystal systems shown in the table. School of Mechanical Engineering Vignan University

TYPES OF CRYSTAL SYSTEMS : 

TYPES OF CRYSTAL SYSTEMS School of Mechanical Engineering Vignan University

BRAVAIS LATTICES : 

BRAVAIS LATTICES In 1850, M. A. Bravais showed that identical points can be arranged spatially to produce 14 types of regular pattern. These 14 space lattices are known as ‘Bravais lattices’. School of Mechanical Engineering Vignan University

14 BRAVAIS LATTICES : 

14 BRAVAIS LATTICES School of Mechanical Engineering Vignan University

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School of Mechanical Engineering Vignan University

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THREE DIMENTIONAL UNIT CELLS / UNIT CELL SHAPES 1 2 3 4 5 6 7

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Primitive ( P ) Body Centered ( I ) Face Centered ( F ) C-Centered (C ) LATTICE TYPES School of Mechanical Engineering Vignan University

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BRAVAIS LATTICES 7 UNIT CELL TYPES + 4 LATTICE TYPES = 14 BRAVAIS LATTICES

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THANK YOU School of Mechanical Engineering Vignan University