Characterization of ultralow thermal conductivity in anisotropic pyrolytic carbon coating for thermal management applications

Impact of irradiation induced dislocation loops on thermal conductivity in ceramics

“…The phase profile exhibits a characteristic linear dependence proportional to materials’ thermal properties . Effective diffusivity vs. modulation frequency determined by appropriately normalizing the slopes extracted from the linear sections of the profiles measured over 10‐100 kHz frequency range are plotted in Figure B . Steeper profile with larger slope and smaller effective diffusivity is a direct indication of thermal conductivity reduction in irradiated samples .…”

“…37 Effective diffusivity vs. modulation frequency determined by appropriately normalizing the slopes extracted from the linear sections of the profiles measured over 10-100 kHz frequency range are plotted in Figure 4B. 56 Steeper profile with larger slope and smaller effective diffusivity is a direct indication of thermal conductivity reduction in irradiated samples. 32 Quantitative determination of conductivity in the plateau region that accounts for transducer layer and considers only profiles that have minimal sensitivity to peak damage and undamaged section of the samples follows a procedure outlined in Riyad et al 37 Table I lists the measured conductivities for both irradiated samples and compares them to the as-received sample.…”

“…Phonon scattering rate −1 ( ) is a combination of the following phonon scattering processes: intrinsic 3-phonon processes, impurities in the as-received sample, and irradiation induced point defects, dislocation loops, and voids added using Mattiesen rule. 56,59 For the intrinsic 3-phonon and impurity scattering we use the relations The impact of irradiation damage on these parameters is negligible compared to the impact on phonon scattering rates. The impact of irradiation damage on phonon scattering rates for individual defect types is described next.…”

“…According to the Klemens‐Callaway approach, thermal conductivity is given by:where , ω‐phonon frequency, T ‐temperature, ћ ‐Plank's constant, k B ‐Boltzmann constant, νs ‐sound velocity, and ω D ‐Debye phonon frequency. Phonon scattering rate is a combination of the following phonon scattering processes: intrinsic 3‐phonon processes, impurities in the as‐received sample, and irradiation induced point defects, dislocation loops, and voids added using Mattiesen rule . For the intrinsic 3‐phonon and impurity scattering we use the relations and , respectively where use B = 1.6 × 10 −18 s/K, = 5.4 × 10 13 Hz, = 409 K, = 3270 m/s and A 0 = 44.1 × 10 −44 s 3 obtained in previous work on unirradiated CeO 2 .…”

Thermal Conductivity of HfTe5: A Critical Revisit

“…The large anisotropy of the lattice thermal conductivity endows HfTe 5 with a great potential for new directional‐heat‐management applications, in which it can act as either a heat spreader or insulator depending on the direction. The low through‐plane thermal conductivity can also be utilized in self‐regulating heaters to protect electronic devices from irreversible damage in the event of overheating by efficiently trapping the heat and giving quick feedback to the protecting system . It can be also used in thermal barrier coating of wearable devices, in which the Joule heat needs to be prevented from flowing through the device to burn skin meanwhile efficiently spreading out (along the in‐plane direction) to prevent overheating of the devices.…”