Phonons
Packets
of sound found present in the lattice as it vibrates … but
the lattice vibration cannot be
heard.
Unlike static lattice model ,
which deals with average positions of atoms in a crystal, lattice
dynamics extends the concept of crystal lattice to an array of atoms with
finite masses that are capable of motion. This motion is not random but
is a superposition of vibrations of atoms around their
equilibrium sites due to the interaction with neighbor atoms.
A collective vibration of atoms in the crystal forms a wave of allowed wavelength
and amplitude.
Just as light is a wave motion that is
considered as composed of particles called photons, we can think of the
normal modes of vibration in a solid as being particle-like. Quantum of lattice vibration is called the
phonon.