Introduction

	University of Nevada Las Vegas		MEG301 Structures and Properties of Solids
	Department of Mechanical Engineering		Fall Semester 2000

Crystal Structures

Crystal: a solid composed of atoms, ions, or molecules arranged in a pattern that is repeated in three dimensions. Examples: metals, alloys, and some ceramic materials.

Crystal Structure: a regular three-dimensional pattern of atoms or ions in space.

Space Lattice: a three-dimensional array of points each of which has identical surroundings

Lattice Point: one point in an array in which all the points have identical surroundings.

Unit Cell: the smallest repetitive pattern (or atomic order) in a crystalline solid.

Lattice Constants: the size and shape of a unit cell can be described by three lattice vectors a, b, and c, originating from one corner of the unit cell. The axial lengths, a, b, and c and the interaxial angles a , b , and g are the lattice constants.

Lattice Constants	Axial Length	Interaxial Angle
	a	a
	b	b
	c	g

Bravais Lattices:

Crystal System	Space Lattice	Axial length and Interaxial Angle
Cubic	Simple cubic	a = b = c, a = b = g = 90⁰
	Body-centered cubic (BCC)
	Face-centered cubic (FCC)
Tetragonal	Simple tetragonal	a = b ¹ c, a = b = g = 90⁰
Tetragonal	Body-centered tetragonal	a = b ¹ c, a = b = g = 90⁰
Orthorhombic	Simple orthorhombic	a ¹ b ¹ c, a = b = g = 90⁰
	Body-centered orthorhombic
	Face-centered orthorhombic
	Base-centered orthorhombic
Rhombohedral	Simple rhombohedral	a = b = c, a = b = g ¹ 90⁰
Hexagonal	Simple hexagonal	a = b ¹ c, = b = 90⁰, g ¹ 120⁰
Monoclinic	Simple monoclinic	a ¹ b ¹ c, a = g = 90^{0 ¹}b
Monoclinic	Base-centered monoclinic	a ¹ b ¹ c, a = g = 90^{0 ¹}b
Triclinic	Simple triclinic	a ¹ b ¹ c, a ¹ b ¹ g ¹ 90⁰

Created by Dr. Wang