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MINDMAP 5 - Coggle Diagram
MINDMAP 5
THERMAL CONDUCTIVITY
heat transfer mechanism
- electrons, holes, phonon obtain more energy than its average when heated
- for metals = electrons, holes, phonons can transfer or conduct thermal energy from hot areas to cooler
- for insulators (eg; dielectric materials) = phonon will delivering the energy
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harmonic approximation
- No thermal expansion
- adibatic and isothermal elastic constants are equal
- elastic constants are independent of pressure and temperature
- heat capacity becomes constants at high temperature
phonons do not interact with each other, in the absence of boundaries lattice defects and impurities, the thermal conductivity is infinite
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- Phonon cannot be used to describe a deviation from equilibrium in one region of the crystal
- the deviation can be describe by wave packet consisting of phonon with range Δk to k
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Phonon mean free path
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Thermal conductivity, k = constant of proportionality between a temperature gradient and rate of energy flow per unit area
- imply and equilibrium situation (energy transfer is a random process in local thermal equilibrium)
- phonon must diffuse through the sample, suffering frequent collisions from got to cooler region
anharmonic effects
phonons collide with each other and the collisions limit the thermal conductivity which is due to the flow of phonons
Phonon-phonon interaction = caused a collision of phonons and a finite mean free path and by several different processes, establishing equilibrium
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