共查询到20条相似文献,搜索用时 15 毫秒
1.
R.K. Kremer K. Graf G.G. Devyatykh A.M. Gibin A.N. Taldenkov 《Solid State Communications》2004,131(8):499-503
The thermal conductivity of isotopically enriched 28Si (enrichment better than 99.9%) was redetermined independently in three laboratories by high precision experiments on a total of four samples of different shape and degree of isotope enrichment in the range from 5 to 300 K with particular emphasis on the range near room temperature. The results obtained in the different laboratories are in good agreement with each other. They indicate that at room temperature the thermal conductivity of isotopically enriched 28Si exceeds the thermal conductivity of Si with a natural, unmodified isotope mixture by 10±2%. This finding is in disagreement with an earlier report by Ruf et al. At ∼26 K the thermal conductivity of 28Si reaches a maximum. The maximum value depends on sample shape and the degree of isotope enrichment and exceeds the thermal conductivity of natural Si by a factor of ∼8 for a 99.982% 28Si enriched sample. The thermal conductivity of Si with natural isotope composition is consistently found to be ∼3% lower than the values recommended in the literature. 相似文献
2.
V. I. Ozhogin A. V. Inyushkin A. N. Taldenkov A. V. Tikhomirov G. É. Popov E. Haller K. Itoh 《JETP Letters》1996,63(6):490-494
The thermal conductivity of chemically, structurally, and isotopically highly pure germanium single crystals is investigated
experimentally in the temperature range from 2 to 300 K. It is found that the thermal conductivity of germanium enriched to
99.99% 70Ge is 8 times higher at the maximum than the thermal conductivity of germanium with the natural isotopic composition.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 6, 463–467 (25 March 1996) 相似文献
3.
A. V. Inyushkin A. N. Taldenkov V. G. Ral’chenko V. I. Konov A. V. Khomich R. A. Khmel’nitskiĭ 《Journal of Experimental and Theoretical Physics》2008,107(3):462-472
The temperature dependences of thermal conductivity κ of polycrystalline CVD diamond are measured in the temperature range from 5 to 410 K. The diamond sample is annealed at temperatures sequentially increasing from 1550 to 1690°C to modify the properties of the intercrystallite contacts in it. As a result of annealing, the thermal conductivity decreases strongly at temperatures below 45 K, and its temperature dependence changes from approximately quadratic to cubic. At T > 45 K, the thermal conductivity remains almost unchanged upon annealing at temperatures up to 1650°C and decreases substantially at higher annealing temperatures. The experimental data are analyzed in terms of the Callaway theory of thermal conductivity [9], which takes into account the specific role of normal phonon-phonon scattering processes. The thermal conductivity is calculated with allowance for three-phonon scattering processes, the diffuse scattering by sample boundaries, the scattering by point and extended defects, the specular scattering by crystallite boundaries, and the scattering by intercrystallite contacts. A model that reproduces the main specific features of the thermal conductivity of CVD diamond is proposed. The phonon scattering by intercrystallite contacts plays a key role in this model. 相似文献
4.
The thermal conductivity of (La0.25Pr0.75)0.7Ca0.3MnO3 manganite has been studied. The isotope substitution of 18O for 16O in this compound leads to a ferromagnetic-antiferromagnetic phase transition at low temperatures. It has been found that the thermal conductivity in the ferromagnetic state is approximately two times higher than in the antiferromagnetic state. It has been shown that the small value of thermal conductivity and its temperature dependence can be due to strong phonon scattering from crystal lattice defects, which are thought of as Jahn-Teller distortions. The parameters of this scattering can be determined within the Debye model of thermal conductivity from a comparison of samples differing in their isotope composition. 相似文献
5.
Abstract Recent advances on the preparation technique of sintered diamond and cubic boron nitride containing small amount of sintering additives having superior thermal and mechanical properties is reviewed. Sintered diamond of lower metallic content (1–5 vol%) shows high hardness (100–150 GPa) and high electrical resistivity (108 ohm-cm) at room temperature. Reaction sintered cubic boron nitride contained 1–3 mole % of magnesium boron nitride shows high thermal conductivity. (7 watt/cm K at RT) 相似文献
6.
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.
相似文献
7.
The thermal diffusivities of UC1 ? xNx of several compositions were measured from 100 to 1000 °K by a laser flash method. The thermal conductivity was separated into electronic and phonon components by assuming the constant Lorenz number. The phonon conductivity showed an anomalous behaviour against composition at low temperatures. The total thermal conductivity of UC1 ? xNx showed a minimum above 300 °K at an intermediate composition which moved to higher carbon content with increasing temperature. This behaviour was explained by the temperature dependence of the lattice and electronic components. 相似文献
8.
《Solid State Communications》1986,58(8):511-514
The temperature dependence of the conductivity of a high-mobility silicon MOSFET is reported for temperatures from 0.2 to 23 K and electron densities from 1 to 20 × 1011cm−2. The results show a strong increase in conductivity with decreasing temperature. However, this rate of increase was observed to rapidly diminish outside of a restricted range of temperature for a given density. The decreasing temperature dependence at the lower temperatures is attributed to the saturation of screening as the effects of broadening become comparable to thermal effects. The diminishing temperature dependence at the higher temperatures puts limits on the applicability of recent calculations for the conductivity. 相似文献
9.
We have measured the thermal conductivity of pressed pellets of 99.999% AgI from 120 K to 500 K using a transient hot wire method. The temperature dependence changes from T?1.3±0.1 at the lowest temperatures to T?1.8±0.1 below the phase transition at 420 K. Above this phase transition where AgI is a superionic conductor we see a weak temperature dependence T+0.5±0.1. These results indicate shortening of the phonon mean free path at high temperatures due to the mobile Ag+ ions. 相似文献
10.
We measured the thermal conductivity of pure SmS and of SmS doped with P, As and Se between 1.5 and 350 K. The lattice thermal conductivity of pure samples and of SmSSe obeys a T? law for temperatures T greater than 150 K, and is very sensitive to point defects in the lattice. The highest values are measured on samples close to the stoichiometric composition. P and As dopants act as phonon scattering centers and considerably reduce the low temperature lattice conductivity. 相似文献
11.
Experimental data on the thermal conductivity K(T) of natural and highly enriched (99.99%) Ge70 crystals with ground and polished surfaces are analyzed in the temperature interval ∼2–8 K. In all samples, the boundary
scattering mechanism predominates in the interval from 2 to 4.0 K. As temperature increases, in highly enriched samples N processes start to contribute to phonon transport and the behavior of K(T) corresponds to viscous Poiseuille flow of a phonon gas. The isotopic scattering mechanism plays a large role in isotopically
nonideal samples.
Fiz. Tverd. Tela (St. Petersburg) 40, 1604–1607 (September 1998) 相似文献
12.
Nonmetallic crystals with high thermal conductivity 总被引:2,自引:0,他引:2
G.A. Slack 《Journal of Physics and Chemistry of Solids》1973,34(2):321-335
Nonmetallic crystals transport heat primarily by phonons at room temperature and below. There are only a few nonmetallic crystals which can be classed as high thermal conductivity solids, in the sense of having a thermal conductivity of > 1 W/cmK at 300K. Thermal conductivity measurements on natural and synthetic diamond, cubic BN, BP and AIN confirm that all of them are high thermal conductivity solids. Studies have been made of the effect on the thermal conductivity of nitrogen impurities in diamond, and oxygen impurities in AIN. The nitrogen impurities scatter phonons mostly from the strain field, the oxygen impurities scatter phonons mostly from the mass defects caused by aluminum vacancies. Pure A1N as well as pure SiC, BeO, BP and BeS conduct heat almost as well as does copper at room temperature, while pure natural and synthetic diamonds conduct heat five times better than copper.All of the nonmetallic solids that are known to possess high thermal conductivity have either the diamond-like, boron carbide, or graphite crystal structure. There are twelve different diamond-like crystals, a few boron carbide-type crystals, and two graphite structure crystals that have high thermal conductivity. Analyses of the rock-salt, fluorite, quartz, corundum and other structures show no candidates for this class. The four rules for finding crystals with high thermal conductivity are that the crystal should have (1) low atomic mass, (2) strong bonding, (3) simple crystal structure, and (4) low anharmonicity. The prime example of such a solid is diamond, which has the highest known thermal conductivity at 300K. 相似文献
13.
In order to evaluate the effect of annealing treatment on the proton conductivity of ??-alumina, the electrical conductivity of Mg-doped polycrystalline ??-alumina kept at 1,873?K under various conditions of the surrounding atmosphere and then cooled in the furnace was measured in the temperature range 1,173?C1,473?K. The H+/D+ isotope effect on the electrical conductivity was also examined under a hydrogen atmosphere at 1,273?K. The protonic conductivity measured at 1,273?K increased with the increase in the activity of oxygen and water vapor in the annealing atmosphere at 1,873?K. It is considered that the solubility limit of magnesium ions in ??-alumina in equilibrium with the small amount of the spinel phase increased with the increase in the activity of oxygen and water vapor at 1,873?K. This enhanced amount of magnesium ions is frozen in a non-equilibrium state to 1,273?K and works as the enriched acceptor dopant for the incorporation of protons. 相似文献
14.
Experimental data on the thermal conductivity K(T) of crystals of natural and highly enriched germanium (99.99%) 70Ge with lapped and polished surfaces are analyzed in the temperature range ∼1.5–8 K. In all the samples in the temperature
range ∼1.5–4 K the standard boundary mechanism of scattering dominates. As the temperature is raised, an isotopic scattering
mechanism is observed in the natural samples. In the highly enriched samples the theoretical values of K(T) turn out to be much smaller than the experimental ones. It is conjectured that a Poiseuille viscous flow regime of the phonon
gas emerges in this case.
Zh. éksp. Teor. Fiz. 114, 1757–1764 (November 1998) 相似文献
15.
The electric conductivity of solid crystallohydrate CdBr2·4H2O was measured at temperatures ranging from room temperature up to 673 K. By means of thermal analysis, infrared spectroscopy and electrochemical methods the conductivity mechanism in certain temperature ranges was assumed. The relatively low conductivity before the beginning of dehydration (≈10?4 S/m, with activation energy of 38.2 kJ/mol)_originates from the movement of H+ ions. With a rise in temperature, the structural changes, due to dehydration, cause a change in the nature of the charge carrier and the conductivity mechanism. Gradual dehydration which starts at ≈310 K activates new charge carriers and causes a sudden increase in the conductivity which remains relatively high (≈1 S/m) up to ≈383 K, until the liberated water, evaporating, leaves the sample. The conductivity of the dehydrated sample is very low (≈10?6 S/m). 相似文献
16.
Yanxia Tang Lihua Wang Chao Zhao 《Applied Physics A: Materials Science & Processing》2014,115(2):379-385
The present work reports the enhancement of the thermal properties in Ag/diamond matrix composites reinforced with chromium carbide coated diamond particles. The coated diamond particles were characterized by x-ray diffraction, x-ray photoelectron spectroscopy and Raman spectra. The composites were synthesized by spark plasma sintering. The chromium carbide coating on the diamond particles resulted in composites exhibiting improved wettability and strong interfacial bonding between the diamond particles and Ag matrix. The composites with coated diamonds showed a low coefficient of thermal expansion of 8.24 × 10?6/K and a high thermal conductivity of 695 W/mK at 60 % particle volume fraction, which greatly outperformed the composites with uncoated diamonds at the same particle volume fraction. The obtained results are useful for synthesizing Ag/diamond composites with greatly improved thermal performance. 相似文献
17.
A. A. Kaminskii V. G. Ral’chenko H. Yoneda A. P. Bol’shakov A. V. Inyushkin 《JETP Letters》2016,104(5):347-352
Isotopically pure 12С and 13С diamonds are synthesized by chemical vapor deposition and impulsive stimulated Raman scattering in these crystals is investigated. The thermal conductivity of 12С isotopically pure damond and natC diamond with natural isotopic composition is measured. Phonon-nondegenerate Stokes lasing based on the χ(3) nonlinearity in the 12С, 13С, and natC diamond “triad” is attained, which opens a new stage in the development of diamond photonics. 相似文献
18.
Results of measurements of conductivity and Hall coefficient in the temperature range 15–300K and of thermal emf in the temperature range 80–400K, carried out on TiS3 samples, are reported. The results indicate that these crystals are semiconducting with extrinsic n-type conductivity. The mobility of the carriers is about 30 cm2/V sec at room temperature, increases up to about 100 cm2/V sec at 100K and drops at lower temperatures. The Seebeck coefficient is in qualitative agreement with these findings but its detailed temperature dependence is not yet understood. 相似文献
19.
A. V. Inyushkin A. N. Taldenkov 《Journal of Experimental and Theoretical Physics》2010,111(5):760-769
Thermal conductivity of paramagnetic Tb3Ga5O12 (TbGG) terbium-gallium garnet single crystals is investigated at temperatures from 0.4 to 300 K in magnetic fields up to 3.25 T. A minimum is observed in the temperature dependence κ(T) of thermal conductivity at T min = 0.52 K. This and other singularities on the κ(T) dependence are associated with scattering of phonons from terbium ions. The thermal conductivity at T = 5.1 K strongly depends on the magnetic field direction relative to the crystallographic axes of the crystal. Experimental data are considered using the Debye theory of thermal conductivity taking into account resonance scattering of phonons from Tb3+ ions. Analysis of the temperature and field dependences of the thermal conductivity indicates the existence of a strong spin-phonon interaction in TbGG. The low-temperature behavior of the thermal conductivity (field and angular dependences) is mainly determined by resonance scattering of phonons at the first quasi-doublet of the electron spectrum of Tb3+ ion. 相似文献
20.
A series of diamond-like carbon (DLC) films with different microstructure were prepared by depositing carbon atoms on diamond surface with incident energy ranging from 1 to 100 eV. The thermal conductivity of the deposited films and the Kapitza resistance between the film and the diamond substrate were investigated. Results show that the average density, the average fraction of sp3 bonding and the thermal conductivity of the DLC films increase first, reaching a maximum around 20–40 eV before decreasing, while the Kapitza resistance decreases gradually with increased deposition energy. The analysis suggests that the thermal resistance of the interface layer is in the order of 10?10 m2K/W, which is not ignorable when measuring the thermal conductivity of the deposited film especially when the thickness of the DLC film is not large enough. The fraction of sp3 bonding in the DLC film decreases gradually normal to the diamond surface. However, the thermal conductivity of the film in normal direction is not affected obviously by this kind of structural variation but depends linearly on the average fraction of sp3 bonding in the entire film. The dependence of the thermal conductivity on the fraction of sp3 bonding was analysed by the phonon theory. 相似文献