Anomalous pressure effect on the thermal conductivity of ZnO, GaN, and AlN from first-principles calculations
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In this paper, the lattice thermal conductivities of bulk ZnO, GaN, and AlN in the normal-pressure wurtzite phase and high-pressure rocksalt phase at room temperature are investigated by solving the phonon Boltzmann transport equation based on first-principles calculations. The results show that the thermal conductivities of the rocksalt ZnO, GaN, and AlN close to the phase-transition pressure are reduced by 73%, 91%, and 34%, respectively, compared to that of corresponding normal-pressure wurtzite structures. Additionally, the thermal conductivity of wurtzite ZnO and GaN exhibits unexpectedly nonmonotonic dependence on pressure; however, for wurtzite and rocksalt AlN the thermal conductivity increases monotonically with the increase of pressure. Detailed phonon mode analysis reveals that the enhanced lattice anharmonicity is responsible for the depressed thermal conductivity of the rocksalt phase. By evaluating the relative contributions of dominant factors affecting lattice thermal conductivity, we find that the nonmonotonic response of thermal conductivity to pressure in wurtzite ZnO and GaN is attributed to the interplay of group velocity and phonon relaxation time. This study provides quantitative understanding of lattice thermal conductivity of ZnO, GaN, and AlN considering the pressure-induced phase transition and highlights the importance of pressure in manipulating lattice thermal conductivity.Keywords:
Wurtzite crystal structure
Analytical solution of the Boltzmann transport equation for phonon transport in Bi 0.95 Sb 0.05 nanowire is obtained.Thermal conductivity was calculated from the analytical solution of the Boltzmann transport equation.We calculate the lattice thermal conductivity of Bi 0.95 Sb 0.05 nanowire as a function of temperature for different wire thicknesses.The results show that thermal conductivity of nanowire can be significantly smaller than the bulk thermal conductivity.We show that low thermal conductivity Bi 0.95 Sb 0.05 nanowire for thermoelectric applications would have a small diameter.
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This paper reports on the theoretical modeling of the phonon thermal conductivity of hollow nanowires and core-and shell nanowires. Both the axial and the radial thermal conductivity of hollow nanowires have been analytically modeled by solving the Boltzmann transport equation. The radial thermal conductivity has been modeled using the ballistic-diffusive heat conduction equations. Results for both axial and radial thermal conductivity are in excellent agreement with the numerical solution of the Boltzmann transport equation
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The investigation of thermal transport is crucial to the thermal management of modern electronic devices. To obtain the thermal conductivity through solution of the Boltzmann transport equation, calculation of the anharmonic interatomic force constants has a high computational cost based on the current method of single-point density functional theory force calculation. The recent suggested machine learning interatomic potentials (MLIPs) method can avoid these huge computational demands. In this work, we study the thermal conductivity of two-dimensional MoS 2 -like hexagonal boron dichalcogenides (H-B 2 VI 2 ; VI = S, Se, Te) with a combination of MLIPs and the phonon Boltzmann transport equation. The room-temperature thermal conductivity of H-B 2 S 2 can reach up to 336 W⋅m −1 ⋅K −1 , obviously larger than that of H-B 2 Se 2 and H-B 2 Te 2 . This is mainly due to the difference in phonon group velocity. By substituting the different chalcogen elements in the second sublayer, H-B 2 VIVI ′ have lower thermal conductivity than H-B 2 VI 2 . The room-temperature thermal conductivity of B 2 STe is only 11% of that of H-B 2 S 2 . This can be explained by comparing phonon group velocity and phonon relaxation time. The MLIP method is proved to be an efficient method for studying the thermal conductivity of materials, and H-B 2 S 2 -based nanodevices have excellent thermal conduction.
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The electronic and structural properties of wurtzite InN, ZnS and CdSe structures are studied using the empirical pseudopotential method (EPM). The principal energy at Γ of wurtzite InN, ZnS and CdSe compounds are calculated. Band structure of wurtzite InN, ZnS and CdSe materials are presented. Other quantity such as bulk modules by meansof our model is calculated.
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In this study, the effect of point defects on the thermal conductivity of UO2 is investigated. Especially, the effects of oxygen vacancy and interstitial are considered. Thermal conductivity of UO2, UO2+0.25 and UO2-0.25 is calculated by solving the phonon Boltzmann equation (BTE) under the relaxation time approximation (RTA). The results show that introducing any defects to the lattice structure of UO2 decreases thermal conductivity significantly. In addition, the results show that the variation of the thermal conductivity of UO2-0.25 is much lower than that of UO2+0.25 in the temperature interval of 300 to 1000 Kelvin.
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Using a combination of equilibrium classical molecular dynamics (within the Green-Kubo formalism) and the Boltzmann transport equation, we study the effect of strain on the ZnO thermal conductivity focusing in particular on the case of hydrostatic and uniaxial strain. The results show that in the case of hydrostatic strain up to $\ifmmode\pm\else\textpm\fi{}4%$, we can obtain thermal conductivity variations of more than 100%, while for uniaxial strains the calculated thermal conductivity variations are comparatively less pronounced. In particular, by imposing uniaxial compressive strains up to $\ensuremath{-}4%$, we estimate a corresponding thermal conductivity variation close to zero. The mode analysis based on the solution of the Boltzmann transport equation shows that for hydrostatic strains, the thermal conductivity variations are mainly due to a corresponding modification of the phonon relaxations times. Finally, we provide evidence that for uniaxial compressive strains the contribution of the phonon relaxations time is balanced by the increase of the group velocities leading to a thermal conductivity almost unaffected by strain.
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