Chapter 5
Solid State Physics
5.1 Basic Concepts and Formulae ................................
Crystal Structure
There are seven crystal systems Cubic, Tetragonal, Orhtorhombic, monoclinic, tri-
clinic, Rhombohedral, Hexagonal. They are distinguished by the axial lengths and
axial angles. The lengths are taken asa, bandc. In the cubic systema=b=cand
the angle between any two axes is a right angle.
Bragg’s equation
2 dsinθ=nλ (5.1)wheredis the distance between parallel diffraction planes,θis the angle between
the incident beam and the diffraction plane andnis the order of diffraction. The
distancedcan be related to the lattice parameters of the crystal cell. In the simple
cubic cell the distance between (100) planes is “a”, the lattice parameter. The dis-
tance between parallel (110) planes passing through lattice points is a/
√
2; for (111),
it is a/
√
- In general distance between parallel planes of indices (hkl) in terms of
the parameter “a” for the cubic system is
d^2 =a^2
h^2 +k^2 +l^2(5.2)
Electrical properties of crystals
The principal attractive force between ions of opposite sign is an electrostatic force.
The repulsive force arises from the interaction of the electron clouds surrounding an
atom. This force arises because of the exclusion principle and is not electrostatic in
nature. Empirically this is represented byb/rn, wherebandnare constants, andr
is the anion-cation distance.
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