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Using a method developed by Prigogine and Henin the thermal conductivity of an anharmonic crystal is obtained to the order λ2. The calculation is performed using the « brownian motion assumption » wich enables us to get results solving relatively simple equations — a correction due to dilatation effects is also included.

This paper reviews the theoretical and experimental works concerning one of the most important parameters of wurtzite gallium nitride – thermal conductivity. Since the heat in gallium nitride is transported almost exclusively by phonons, its thermal conductivity has a temperature behavior typical of most nonmetallic crystals: the thermal conductivity increases proportionally to the third power of temperature at lower temperatures, reaches its maximum at approximately 1/20 of the Debye temperature and decreases proportionally to temperature at higher temperatures. It is shown that the thermal conductivity of gallium nitride (depending on fabrication process, crystallographic direction, concentration of impurity and other defects, isotopical purity) varies significantly, emphasizing the importance of determining this parameter for the samples that closely resemble those being used in specific applications. For isotopically pure undoped wurtzite gallium nitride, the thermal conductivity at room temperature has been estimated as high as 5.4 W/(cm·K). The maximum room temperature value measured for bulkshaped samples of single crystal gallium nitride has been 2.79 W/(cm·K).

We investigate the harmonic and anharmonic contributions to the phonon spectrum of lead telluride and perform a complete characterization of how thermal properties of PbTe evolve as temperature increases. We analyze the thermal resistivitys variationwith temperature and clarify misconceptions about existing experimental literature. The resistivity initially increases sublinearly because of phase space effects and ultra strong anharmonic renormalizations of specific bands. This effect is the strongest factor in the favorable thermoelectric properties of PbTe, and it explains its limitations at higher T. This quantitative prediction opens the prospect of phonon phase space engineering to tailor the lifetimes of crucial heat carrying phonons by considering different structure or nanostructure geometries. We analyze the available scattering volume between TO and LA phonons as a function of temperature and correlate its changes to features in the thermal conductivity. ; Funding Agencies|Marie Curie Actions from the European Union [PIIFR-GA-2011-911070]; American Chemical Society Petroleum Research Fund [54075-ND10]; National Science Foundation [1434897]; Action de Recherches Concertees (ARC) from the Communaute Francaise de Belgique [10/15-03]; EU FP7 [RI-283493, RI-312763]; Swedish Research Council (VR) program [637-2013-7296]

"Date of Issue: January 29, 1954." ; Includes bibliographical references (page 8) ; Carbide and Carbon Chemicals Company a division of Union Carbide and Carbon Corporation acting under U.S. Government Contract ; Mode of access: Internet.

In the DARPA Thermal Ground Plane (TGP) program[1],we are developing a new thermal technology that will enable a monumental thermal technological leap to an entirely new class of electronics, particularly electronics for use in high-tech military systems. The proposed TGP is a planar, thermal expansion matched heat spreader that is capable of moving heat from multiple chips to a remote thermal sink. DARPA's final goals require the TGP to have an effective conductivity of 20,000 W/mK, operate at 20g, with minimal fluid loss of less than 0.1%/year and in a large ultra-thin planar package of 10cmx20cm, no thicker than 1mm. The proposed TGP is based on a heat pipe architecture[2], whereby the enhanced transport of heat is made possible by applying nanoengineered surfaces to the evaporator, wick, and condenser surfaces. Ultra-low thermal resistances are engineered using superhydrophilic and superhydrophobic nanostructures on the interior surfaces of the TGP envelope. The final TGP design will be easily integrated into existing printed circuit board manufacturing technology. In this paper, we present the transport design, fabrication and packaging techniques, and finally a novel fluorescence imaging technique to visualize the capillary flow in these nanostructured wicks. ; United States. Defense Advanced Research Projects Agency (SSC SD Contract No. N66001-08-C-2008)

Strategies for tuning the thermal conductivity of crystals by means of external fields are rare. Here, we predict the existence of large magnetophononic effects in materials that undergo antiferromagnetic (AFM) ↔ ferromagnetic (FM) phase transitions, which allow for the modulation of the lattice heat conductivity, κL, via the application of magnetic fields. Specifically, by using first-principles methods we predict a large and anomalous κL increase of ≈40% for the metamagnetic phase transition occurring in bulk FeRh near room temperature. The disclosed magnetophononic effects are caused by large anharmonic spin-phonon couplings, namely, significant differences in the phase space of allowed phonon-phonon collision processes taking place in the respective AFM and FM phases. ; We acknowledge financial support by MCIN/AEI/10.13039/501100011033 under Grant No. PID2020-119777GB-I00, the "Ramón y Cajal" fellowship RYC2018-024947-I, and the Severo Ochoa Centres of Excellence Program (CEX2019-000917-S), and by the Generalitat de Catalunya under Grant No. 2017 SGR 1506. Calculations were performed at the Centro de Supercomputación de Galicia (CESGA) within action FI-2021-1-0007 of the Red Española de Supercomputación (RES). We thank Michael Wolloch and Jesús Carrete for useful discussions. ; With funding from the Spanish government through the 'Severo Ochoa Centre of Excellence' accreditation (CEX2019-000917-S). ; Peer reviewed