Dependence Of Lattice Thermal Conductivity Research Articles

The temperature dependence of thermal conductivity for lherzolites from the North China Craton and the associated constraints on the thermodynamic thickness of the lithosphere

In this study, the authors aimed to compute the lithospheric thickness beneath the North China Craton (NCC) by combining the measurement of the thermophysical properties of lherzolite xenoliths from the Cenozoic basalts in North China with the corresponding geothermal data, thus providing geothermal constraints for the lithospheric thinning beneath the NCC. Based on the precise measurement of the thermal diffusivity, specific heat capacity at high temperatures, and density at room temperature for lherzolites from the NCC, the temperature dependence of lattice thermal conductivity for lherzolites was obtained. Combining with the surface heat flow, heat production of rocks and other relevant conditions, the average thickness of the lithosphere beneath the NCC and the lithospheric thickness of secondary massifs were computed, and we identified the relationship between depth and temperature beneath the NCC and each secondary massif. The computed lithospheric thickness is highly consistent with the results of geophysical observations. The computation results of this study indicate that the average lithospheric thickness of the current NCC and the average thickness of the eastern NCC were 101 and 75 km, the lithospheric thickness of the Ordos block increases from 110 km in the east to approximately 200 km in the west, and the average thickness is 141 km, that were thinner than that in the Archean era (200 km) by approximately 100, 125 and 60 km. These results reveal that, in addition to eastern NCC, the Taihang orogenic belt and Ordos block have also experienced varying degrees of thinning with a thinning centre oriented in the north–south direction, consistent with the direction of the thinning centre along the Tanlu fault zone beneath the east NCC.

Effect of Parameters on Lattice Thermal Conductivity in Germanium Nanowires

Modified Callaway's theory was used to calculate lattice thermal conductivity (LTC) of Germanium nanowires. Results are compared to those of experimental values of the temperature dependence of LTC for nanowire diameters of 62, 19, and 15nm. In this calculation, both longitudinal and transverse modes are taken into account. Scattering of phonons is assumed to be by nanowire boundaries, imperfections, dislocations, electrons, and other phonons via both normal and Umklapp processes. Effect of parameters, phonon confinement and imperfections in limiting thermal conductivity for the nanowires under considerations are investigated. The suppression in thermal conductivity of these nanowires is arise from electron-phonon scattering and phonon-boundary scattering at low temperatures, while at high temperatures is due to imperfections and intrinsic properties.

Lattice thermal conductivity of MgO at conditions of Earth’s interior

Thermal conductivity of the Earth's lower mantle greatly impacts the mantle convection style and affects the heat conduction from the core to the mantle. Direct laboratory measurement of thermal conductivity of mantle minerals remains a technical challenge at the pressure-temperature (P-T) conditions relevant to the lower mantle, and previously estimated values are extrapolated from low P-T data based on simple empirical thermal transport models. By using a numerical technique that combines first-principles electronic structure theory and Peierls-Boltzmann transport theory, we predict the lattice thermal conductivity of MgO, previously used to estimate the thermal conductivity in the Earth, at conditions from ambient to the core-mantle boundary (CMB). We show that our first-principles technique provides a realistic model for the P-T dependence of lattice thermal conductivity of MgO at conditions from ambient to the CMB, and we propose thermal conductivity profiles of MgO in the lower mantle based on geotherm models. The calculated conductivity increases from 15 -20 W/K-m at the 670 km seismic discontinuity to 40 -50 W/K-m at the CMB. This large depth variation in calculated thermal conductivity should be included in models of mantle convection, which has been traditionally studied based on the assumption of constant conductivity.

Effect of normal processes on thermal conductivity of germanium, silicon and diamond

The effect of normal scattering processes is considered to redistribute the phonon momentum in (a) the same phonon branch — KK-S model and (b) between different phonon branches — KK-H model. Simplified thermal conductivity relations are used to estimate the thermal conductivity of germanium, silicon and diamond with natural isotopes and highly enriched isotopes. It is observed that the consideration of the normal scattering processes involving different phonon branches gives better results for the temperature dependence of the thermal conductivity of germanium, silicon and diamond with natural and highly enriched isotopes. Also, the estimation of the lattice thermal conductivity of germanium and silicon for these models with the consideration of quadratic form of frequency dependences of phonon wave vector leads to the conclusion that the splitting of longitudinal and transverse phonon modes, as suggested by Holland, is not an essential requirement to explain the entire temperature dependence of lattice thermal conductivity whereas KK-H model gives a better estimation of the thermal conductivity without the splitting of the acoustic phonon modes due to the dispersive nature of the phonon dispersion curves.

Lattice thermal conductivity of disordered binary alloys

We present here a formulation for the calculation of the configuration averaged lattice thermal conductivity in random alloys. Our formulation is based on the augmented-space theorem, introduced by Mookerjee [J. Phys. C 6, L205 (1973)], combined with a generalized diagrammatic technique. The diagrammatic approach simplifies the problem of including effects of disorder corrections to a great extent. The approach allows us to obtain an expression for the effective heat current in the case of disordered alloys, which in turn is used in a Kubo-Greenwood type formula for the thermal conductivity. We show that disorder scattering renormalizes the phonon propagators as well as the heat currents. The corrections to the current terms have been shown to be related to the self-energy of the propagators. We also study the effect of vertex corrections in a simplified ladder diagram approximation. A mode dependent diffusivity ${D}_{\ensuremath{\gamma}}$ and then a total thermal diffusivity averaged over different modes are defined. Schemes for implementing the said formalism are discussed. A few initial numerical results on the frequency and temperature dependence of lattice thermal conductivity are presented for NiPd alloy and are also compared with experiment. We also display numerical results on the frequency dependence of thermal diffusivity averaged over modes.

Temperature Dependence of Lattice Thermal Conductivity for some I-III-VI2 Group Compound Semiconductors

Callaway formula is used to invesfigate the lattice thermal conductivity for nine compounds from the
 ternary group I-III-VI2 semicanductors at the temperature range from 5 to 300K. The maximum
 conductivities are found to be inthe tenrperature range 5-15K.The effects of the Debye temperature on
 lattice thermal conductivity as weil as maximum conductivity are invesfigated in some details. Many
 imperical formula are found to relate these compounds with their lattice thermal conductivities. The
 effects of carrier impurities (N) on this type of conductivity for the compound CuInSe2 are investigated
 and the N^ dependence is fcrund.

Theoretical Calculations of the Temperature and Impurity Dependence of the Lattice Thermal Conductivity of the ZnSnAs2 Semiconductor Compound

The Callaway models are used to calculate lattice thermal conductivity for ZnSnAs2 Semiconductor in the temperature range (2-300) K The dependence of lattice thermal conductivity on temperature and impurity concentration as well as the strength of scattering are discussed, The maximum thermal conductivity for elven samples investigated are appears at the temperature 21K. is 3.54 W/cm.K,This reduces to 0.093 W/cm.K for impurity concentrations from 0.21x102° cm-3 to 10023 cm-3. The scattering strength is also investigated and found to be equal to -0.7203.

Thermoelectric properties of Ag2Se

To obtain information on the temperature and concentration dependence of thermoelectric quality factor Z and to clarify the nature of scattering in Ag2Se a study was made of electrical conductivity σ, thermo-emf α, and thermal conductivity ϰ in silver selenide over the temperature range T=80–450°K at concentration levels of 2–43·1024 m−3. It is shown that in Ag2Se the Lorentz number L, determined experimentally from the electronic fraction of the thermal conductivity, is less than the Sommerfeld number Lo. Calculation of L/Lo(n) performed with a theory considering inelastic scattering of carriers, shows that the inelasticity is produced by electron interaction. Comparison of experimental data on the temperature dependence of lattice thermal conductivity with theory permits the conclusion that in Ag2Se in range 80–300°K the basic role in phonon scattering is played by three-phonon Umklapp processes. It is shown that with increase in T and decrease in n the thermoelectric quality factor of silver selenide increases. The highest value of Z was achieved in a specimen with electron concentration n=2·1024 m−3 at T=320°K. The rapid decrease in Z upon phase transition is related to discontinuous decrease in α and σ at this point.

Boundary scattering of phonons in fine-grained hot-pressed Ge-Si alloys. I. The dependence of lattice thermal conductivity on grain size and porosity

The thermal conductivity of polycrystalline Ge30Si70 has been determined at and above room temperature for samples having a wide range of porosity and mean grain diameter. It has been established that the thermal conductivity at 300K is completely dominated by the lattice contribution and that its value varies linearly with the porosity. It has, therefore, been possible to calculate the lattice conductivity at zero porosity and to show how this varies with the grain size. The lattice conductivity is equal to 8.2 M m-1 K-1 for fully dense large-grained Ge30Si70 at 300K and falls to 4.3 W m-1 K-1 when the mean grain diameter is reduced to 2 mu m. It is shown that there is a significant contribution to the heat transfer from thermal radiation at 600K; when this contribution is taken into account it is found that the lattice conductivity at this temperature falls from 5.8 W m-1 K-1 when the grain size is very large to 3.7 W m-1 K-1 at a mean grain diameter of 2 mu m. Less comprehensive results are also reported for Ge70Si30.

Ionicity dependence of lattice thermal conductivity in tetrahedral semiconductors

The lattice thermal conductivity of A N B B- N tetrahedral semiconductors is described in terms of simple parameters, including the melting point and crystal (Phillips) ionicity. Comparison of results with experimental data shows an overall accuracy of about 15%.