The heat capacity of the lattice. High temperature Prepared: Әділбек Оңалбек
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The heat capacity of the lattice. High temperaturePrepared: Әділбек ОңалбекКөшербай ЕржігітПахратдинов АлматСенімтайқызы ГүлімШалман ӘділетАширмухамбетов Б.Оспанжан ДиасDebye approximation. The first two Brillouin zones of a square lattice are replaced by a circle with the same total area, and the entire spectrum is approximated by a linear dispersion law inside this circles. Debye function The maximum quantum of energy that can excite lattice vibrations expresses energy = specific heat capacity at all temperatures in terms of one empirical parameter At very low temperatures, modes with frequencies hws(k) >> kwT make a negligible contribution 1. Even for a crystal with a polyatomic basis, the sum over s cannot be take into account optical modes, since their frequencies are limited from below 2. Dispersion law of three acoustic branches w = ws(k) - limiting form for long wavelengths w = cs(k) k. 3. Integration over the first Brillouin zone in k-space can be replaced by integration over the entire k-space The Debye approximation for the acoustic branch and the Einstein approximation for the optical branch. The first Brillouin zone is replaced by a circle with the same area, the acoustic branch is approximating is controlled by a linear branch inside the circle, and the optical branch by a branch with a constant frequency experimental methods for determining the photon spectrumNeutron and photon scattering studies are different ways of analyzing the phonon spectrum - they are characterized by completely different relationships between energy and momentumжүктеу/скачать 60.27 Kb. Достарыңызбен бөлісу:
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