Vibrational motions of the ions and thermal effects
Hereafter we shall afford the problem of the motions of the ions around their equilibrium positions in an ideal (disorder- and defect-free) crystal. The motions are called lattice vibrations. The Born-Oppenheimer separation and the adiabatic approximation (§7.1) will be implicit and the concepts involved in the description of the normal modes (§10.6) in the harmonic approximation will be used. In fact, the crystal cell will be considered as a molecular unit: its normal modes propagate along the crystal with a phase factor, in view of the spatial periodicity.
KeywordsNormal Mode Dispersion Curve Sound Velocity Vibrational Spectrum Debye Temperature
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