Crystal lattice and unit cell

Crystal lattice:  A regular 3-dimensional arrangement of points in space is known as crystal lattice. There are only 14 possible crystal lattices. They are known as bravies lattice.

he Seven Categories of Bravais Unit Cells

Category		Edge Lengths		Internal Angles
Cubic		(a = b = c)		(a = �/i> = g = 90o)
Tetragonal		(a = b  c)		(a = �/i> = g = 90o)
Monoclinic		(a  b  c)		(a = �/i> = 90o  g)
Orthorhombic		(a  b  c)		(a = �/i> = g = 90o)
Rhombohedral		(a = b = c)		(a = �/i> = g  90o)
Hexagonal		(a = b  c)		(a = �/i> = 90o, g = 120o)
Triclinic		(a  b  c)		(a  �/i>  g  90o)

Unit cell : It is smallest portion of crystal lattice which whwn repeated again and again in all the direction is called unit cell.

There are 6 parameters of unit cell:a,b,c - Edge lengthalpha, beta, gama : Bond angle

There are two types of unit cell:1.Primitive uit cell2.Centered unit cell

The simple cubic unit cell is the simplest repeating unit in a simple cubic structure. Each corner of the unit cell is defined by a lattice point at which an atom, ion, or molecule can be found in the crystal. By convention, the edge of a unit cell always connects equivalent points.

he body-centered cubic unit cell is the simplest repeating unit in a body-centered cubic structure. Once again, there are eight identical particles on the eight corners of the unit cell. However, this time there is a ninth identical particle in the center of the body of the unit cell.

The face-centered cubic unit cell also starts with identical particles on the eight corners of the cube. But this structure also contains the same particles in the centers of the six faces of the unit cell, for a total of 14 identical lattice points.