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排序方式: 共有199条查询结果,搜索用时 31 毫秒
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3.
Ashoka Bali Il-Ho Kim Peter Rogl Ramesh Chandra Mallik 《Journal of Electronic Materials》2014,43(6):1630-1638
The thermoelectric figure of merit (zT) can be increased by introduction of additional interfaces in the bulk to reduce the thermal conductivity. In this work, PbTe with a dispersed indium (In) phase was synthesized by a matrix encapsulation technique for different In concentrations. x-Ray diffraction analysis showed single-phase PbTe with In secondary phase. Rietveld analysis did not show In substitution at either the Pb or Te site, and this was further confirmed by room-temperature Raman data. Low-magnification (~1500×) scanning electron microscopy images showed micrometer-sized In dispersed throughout the PbTe matrix, while at high magnification (150,000×) an agglomeration of PbTe particles in the hot-pressed samples could be seen. The electrical resistivity (ρ) and Seebeck coefficient (S) were measured from 300 K to 723 K. Negative Seebeck values showed all the samples to be n-type. A systematic increase in resistivity and higher Seebeck coefficient values with increasing In content indicated the role of PbTe-In interfaces in the scattering of electrons. This was further confirmed by the thermal conductivity (κ), measured from 423 K to 723 K, where a greater reduction in the electronic as compared with the lattice contribution was found for In-added samples. It was found that, despite the high lattice mismatch at the PbTe-In interface, phonons were not scattered as effectively as electrons. The highest zT obtained was 0.78 at 723 K for the sample with the lowest In content. 相似文献
4.
X. Yan A. Grytsiv G. Giester E. Bauer P. Rogl S. Paschen 《Journal of Electronic Materials》2011,40(5):589-596
Type I clathrates have been considered as promising thermoelectric materials due to their special structural characteristics:
the “rattling” guest atoms in the larger of the two cages of the clathrate I structure are frequently held responsible for
the low lattice thermal conductivity. By single-crystal x-ray diffraction, we investigated the quaternary clathrates Ba8Cu5Si
x
Ge41−x
(x = 6, 18, 41). Rietveld refinements confirmed that the clathrates in this system crystallize with cubic primitive symmetry,
in the type I clathrate structure, and that no phase transitions occur in the temperature range investigated (100 K to 300 K).
We derive the concentration dependencies of the Debye temperature, the Einstein temperatures, the static disorder parameters,
and the size of the two cages and argue that these dependencies underpin the previously assumed different bonding character
of the Ba guest atoms in the larger and smaller cages. The linear thermal expansion coefficients for the samples are derived. 相似文献
5.
I. Zeiringer N. Melnychenko-Koblyuk A. Grytsiv E. Bauer G. Giester P. Rogl 《Journal of Phase Equilibria and Diffusion》2011,32(2):115-127
In the Au-Ba-Ge system the clathrate type I solid solution, Ba8Au
x
Ge46−x−y
□
y
, extends at 800 °C from binary Ba8Ge43□3 (□ is a vacancy) to Ba8Au6Ge40. For the clathrate phase (1 ≤ x ≤ 6) cubic primitive symmetry (space group Pm[`3]n Pm{\bar{{3}}}n ) was confirmed by x-ray powder diffraction assisted by x-ray single crystal analyses of Ba8Au4.6Ge40.3□1.1. The lattice parameters of the solid solution show an almost linear increase with increasing gold content. Site preference
from x-ray refinement shows that gold atoms preferably occupy the 6d site in random mixture with Ge and vacancies, which vanish
at the solubility limit. Clathrate type ΙX (Ba6Ge25 type) has a maximum solubility of 2.7 at.% gold at 800 °C. Phase equlilibria at 800 °C are characterized by four ternary
phases in the investigated region up to 33.3 at.% barium. The homogeneity range of Ba(Au1−x
Ge
x
)2 (AlB2-type) and BaAu1+x
Ge3−x
has been established: Ba(Au1−x
Ge
x
)2 extends from BaAu0.5Ge1.5 to BaAu0.9Ge1.1 and BaAu1+x
Ge3−x
from BaAu1.1Ge2.9 (BaNiSn3-type) to BaAu2.7Ge1.3 (Ce(Ni,Sb)4-type). The crystal structures of two phases in the gold-rich part have been determined from single crystal x-ray data and
were found to form new structure types: BaAu3Ge with BaAu3Ge-type (space group P4/nmm, a = 0.6459(2), c = 0.5487(2) nm) and BaAu5+x
Ge2−x
(x = 0, BaAu5Si2-type, space group Pnma, a = 0.8981(2), b = 0.7106(2) and c = 1.0363(2) nm), the latter revealing with increasing gold content a closely related derivative structure type (BaAu5.3Ge1.7,
a = a\textBaAu5 \textSi2 , b = b\textBaAu5 \textSi2 , c = 2c\textBaAu5 \textSi2 a = a_{{{\text{BaAu}}_{5} {\text{Si}}_{2} }} ,\;b = b_{{{\text{BaAu}}_{5} {\text{Si}}_{2} }} ,\;c = 2c_{{{\text{BaAu}}_{5} {\text{Si}}{}_{2}}} ). Transport properties and particularly the thermoelectric behavior were studied for Ba8Au6Ge40. 相似文献
6.
Alloys from the solid solution Ce1−xThxPt3Si (x = 0.0, 0.02, 0.04, 0.08, 0.1, 0.2 and 1.0) were prepared by arc-melting. X-ray Rietveld powder analyses revealed that alloys in the compositional range 0 ≤ x ≤ 0.2 crystallize with the CePt3B-type with a random distribution of Ce and Th atoms in positions 1(b) (1/2, 1/2, z) of the noncentrosymmetric space group P4mm. Th-doping results in a rapid suppression of the superconductivity. The alloy with x = 0.02 shows the onset of superconducting state at Tc = 400 mK, while that with x = 0.04 remains in normal metallic state at least down to 70 mK. 相似文献
7.
X. Yan M. Falmbigl G. Rogl A. Grytsiv A. Prokofiev E. Bauer P. Rogl M. Zehetbauer S. Paschen 《Journal of Electronic Materials》2013,42(7):1330-1334
High-pressure torsion (HPT), as a technique to produce severe plastic deformation, has been proven effective to improve the thermoelectric performance of skutterudites. In this report, we present microstructural and thermoelectric properties of the clathrate Ba8Cu3.5Ge41In1.5 processed by HPT. The sample was synthesized from high-purity elements, subsequently annealed, ball milled, and hot pressed, and finally subject to HPT. Compared with the ball-milled and hot-pressed sample, the HPT-processed sample has higher electrical resistivity and Seebeck coefficient, and lower thermal conductivity, electron concentration, and mobility, which is attributed to the reduced grain size and increased density of dislocations, point defects, and cracks. No essential improvement of the dimensionless thermoelectric figure of merit is observed in the investigated temperature range, questioning the universal versatility of this technique for improvement of thermoelectric materials. 相似文献
8.
BaPt5Si12 has been synthesized by argon arc melting the elements. The structure was solved by direct methods from Kappa CCD intensity data. The novel silicide crystallizes in a unique monoclinic structure type: space group C2/m; a = 0.61327(2) nm, b = 3.23481(8) nm, c = 0.61180(1) nm, β = 90.130(2)°. The structure of BaPt5Si12 is characterized by Pt atoms, which are all arranged in planes parallel x–z resulting in tetrahedral coordination for Si1, Si2, Si3 and Si4 atoms and more complex distorted polyhedra around Si5 and Si6 atoms. Three voids were encountered in the structure at the centres of an Achimedian antiprism and two cube-octahedra. These voids do not show any residual electron densities. BaPt5Si12 turns out to be metallic; no phase transitions are found within the temperature range from 300 mK to 300 K. The overall resistivity is rather large, presumably a consequence of the voids in the crystal structure. Additionally, the quite complex crystal structure gives rise to intricate phonon modes. 相似文献
9.
Gerda Urbach 《Journal of the American Oil Chemists' Society》1965,42(11):927-930
Homologous aliphatic γ- or δ-lactones are separated by thin-layer chromatography on a mixture of kieselguhr G and silica gel
G (1:8). The thin-layer plates are chromatographically impregnated with methanol as the stationary phase and developed 3 times
with light petroleum (bp 80–100C) saturated with methanol. γ- And δ-lactones can be separated from each other on the same
adsorbent with a 1:1 mixture of light petroleum (bp 30–40C) and isopropyl ether. The systems can be combined 2-dimensionally.
The lactones are detected by spraying the chromatoplates either with a 2% solution of iodine in methanol or with alkaline
hydroxylamine followed by ferric chloride and acetic acid. These methods were used for the tentative identification of δ-C10–16 lactones in commercial Australian butteroil. 相似文献
10.
Köhler K Lellouch AC Vollmer S Stoevesandt O Hoff A Peters L Rogl H Malissen B Brock R 《Chembiochem : a European journal of chemical biology》2005,6(1):152-161
Cellular signal transduction proceeds through a complex network of molecular interactions and enzymatic activities. The timing of these molecular events is critical for the propagation of a signal and the generation of a specific cellular response. To define the timing of signalling events, we introduce the combination of high-resolution confocal microscopy with the application of small-molecule inhibitors at various stages of signal transduction in T cells. Inhibitors of Src-family tyrosine kinases and actin dynamics were employed to dissect the role of the lymphocyte-specific tyrosine kinase Lck in the formation and maintenance of T cell receptor/CD3-dependent contacts. Anti-CD3epsilon-coated coverslips served as a highly defined stimulus. The kinetics of the recruitment of the yellow fluorescent protein-tagged signalling protein ZAP-70 were detected by high-resolution confocal microscopy. The analysis revealed that at 5 min after receptor engagement, Lck activity was required for maintenance of contacts. In contrast, after 20 min of receptor engagement, the contacts were Lck-independent. The relevance of the timing of inhibitor application provides a pharmacological concept for the maturation of T cell-substrate contacts. 相似文献