Microstructural disorder is the main reason RuS₂ has low thermal conductivity.
However, internal effects like stronger phonon–phonon Umklapp scattering also play a smaller role.
When two phonons collide, their combined momentum goes outside the crystal’s Brillouin zone (the allowed region for vibrations). Umklapp scattering reverses the direction of phonon motion, it acts like friction for heat. Every time this happens, part of the heat flow is canceled or redirected, so less heat is carried forward.
At low temperatures, phonons don’t have enough energy to reach outside the Brillouin zone — so Umklapp processes are rare so heat moves easily. At high temperatures, phonons have more energy → more collisions → more Umklapp scattering → thermal conductivity drops.
The Debye–Callaway model shows that grain boundary and defect scattering in RuS₂ are about ten times stronger than in FeS₂. Equation of Debye–Callaway model of thermal conductivity
θD = Debye temperature
v is the average phonon sound velocity, ω is the phonon frequency, τ is the relaxation time.
A describes the intensity of scattering by point defects,
B is proportional to the intensity of phonon-phonon Umklapp scattering
D is the characteristic distance between diffusive boundary scattering events
https://iopscience.iop.org/article/10.1088/1361-648X/ae0b21
0 comments:
Post a Comment