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1
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- Packets of sound found present in the lattice as it vibrates … but
the lattice vibration cannot be
heard.
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2
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- Considering the regular lattice of atoms in a uniform solid material,
you would expect there to be energy associated with the vibrations of
these atoms. But they are tied together with bonds, so they can't
vibrate independently. The vibrations take the form of collective modes
which propagate through the material.
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3
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- Propagating lattice vibrations can be considered to be sound waves, and
their propagation speed is the speed of sound in the material.
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4
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- The vibrational energies of molecules, e.g., a diatomic molecule, are
quantized and treated as quantum harmonic oscillators. Quantum harmonic
oscillators have equally spaced energy levels with separation DE = hn.
So the oscillators can accept or lose energy only in discrete units of
energy hn.
- The evidence on the behavior of vibrational energy in periodic solids is
that the collective vibrational modes can accept energy only in discrete
amounts, and these quanta of energy have been labeled
"phonons". Like the photons of electromagnetic energy, they
obey Bose-Einstein statistics.
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5
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6
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7
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8
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9
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10
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Notes
