摘要:

The binary antimonide compounds of the skutterudite family have a good potential for thermoelectric applications as recent results at the Jet Propulsion Laboratory (JPL) have shown. However, the room temperature thermal conductivity of these materials is about 10 Wm−1K−1with an estimated 80% contribution from the lattice. To achieve maximumZTvalues, the lattice thermal conductivity needs to be lowered. Because the lattice thermal conductivity of solid solutions can substantially decrease due to the addition of point defect phonon scattering (all state of the art thermoelectric materials are solid solutions), a study of the formation of solid solutions between the antimonide skutterudite compounds is of interest. The existence of CoP3‐CoAs3and CoAs3‐CoSb3solid solutions was already reported in the literature. The preparation and characterization of bothp‐type andn‐type CoSb3‐IrSb3solid solutions by several techniques is reviewed in this paper. The homogeneity of the samples and the existence of solid solutions were investigated using mass density measurements, X‐ray diffractometry, microprobe analysis and optical microscopy. The thermal conductivity, the electrical resistivity, and the Hall mobility were measured from 25 to 500 °C. Experimental results showed that solid solutions were successfully formed in a wide range of compositions. Some immiscibility was observed but may be due to the preparation conditions. The changes in the thermoelectric properties indicated the influence of a strong point defect scattering, resulting in large decreases in Hall mobility and thermal conductivity. The potential for highZTvalues in CoSb3‐IrSb3solid solutions is discussed. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46830

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

This paper describes the thermoelectric properties and the microstructures of ribbons with various boron contents of (FeSi2)1−xBx(x=0∼0.5) fabricated by a spin‐casting technology. The mixture of the &agr; and &egr; phases with metallic properties appears in the as‐fabricated ribbons. When the ribbons were annealed, the &bgr; phase was observed belowx=0.2, and the &bgr; and Si phases were observed abovex=0.3. A long period superlattice of the &bgr; phase was observed atx=0.5. The annealed ribbons have the negative sign of thermoelectric power belowx=0.2. Asxincreases, the thermoelectric power of the annealed ribbon increases to a maximum atx=0.03, while that of the annealed bulk decreases to a minimum atx=0.03. The power factor of the annealed ribbon increases to a maximum atx=0.03, above which it decreases. The energy ofEh+Edcalculated from the slope of plot of &rgr;/Tversus 1/Tbetween 300 and 400 K decreases with increasingx, whereEhis the activation energy of the hopping process,Edis the activation energy of donor, and &rgr; is the electrical resistivity. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46839

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

In a series of experiments designed to evaluate the possibility of lowering the lattice thermal conductivity of silicon‐germanium alloys through the formation of an inert, intragranular nanophase, a number ofp‐type Si‐20 at. % Ge alloys, with a nominal doping level of 0.5 at. % boron, were prepared with varying amounts of fullerite, a mixture of 90% C60+10% C70with a particle size of 0.7 nm. The alloys were synthesized by mechanical alloying (MA) and the fullerite was added at various stages of the preparation sequence. Compacts consolidated by hot pressing at temperatures of 1200 °C to 1265 °C were found to be fully dense and homogeneous. Each compact was characterized by Hall effect at room temperature and also by electrical resistivity, Seebeck coefficient, and thermal diffusivity measurements to 1000 °C. A reduction in thermal conductivity of up to 22% compared to standardp‐type alloys was observed in samples containing 0.8 weight percent additions. In this study, a maximum integrated average figure of merit,Z, between 300 and 1000 °C of 0.65×10−3 °C−1was obtained, corresponding to 0.4 weight percent addition of fullerite. Observation of selected samples by transmission electron microscopy revealed that the fullerite reacted with silicon to form nanophase SiC inclusions. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46802

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We present the early results of our ongoing effort to identify and characterize new TE materials. Using the linear muffin‐tin orbital method, we have studied the shape of the eigenenergy surfaces of the conduction electrons in Si and other TE materials. We describe a multi‐valley multi‐band computational approach in which we perform the Fermi‐integrations directly over the 3D eigenenergy surfaces. Furthermore, by performing these integrations against a delta‐function in carrier energy, &egr;, we are able to characterize the geometric non‐scattering structural aspects of the material in terms of a ‘‘partial conductivity’’ function, &sgr;(&egr;). From this standpoint, it is possible to quantitatively compare the TE properties of different materials within the same structural family, and to gain some insight into the TE structure/function relationship. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46789

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Theoretical methods of investigating of transport properties in solids under large temperature gradients are grounded. The nonlinear and non‐local expressions for current density and heat flow are obtained with degenerated of current carriers gas. A number of new effects with large temperature gradients have been tested. Use of large temperature gradients leads to the increasing of the thermoelectric figure of merit. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46806

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The methods for optimization of thermoelectric powder materials are discussed. Possibilities to optimize powder thermoelectric materials by computer‐aided modelling are demonstrated. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46814

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

IrSb3belongs to a large family of compounds with the skutterudite crystal structure (CoAs3). The peritectic decomposition temperature of IrSb3is 1141 °C. The growth of large crystals of IrSb3by conventional growth techniques is not straightforward. Single phase, polycrystalline samples were prepared by a liquid‐solid sintering technique. Samples were characterized by microprobe analysis, X‐ray diffractometry and density measurements. As‐prepared IrSb3samples showp‐type conductivity andn‐type samples were prepared by addition of platinum. Seebeck coefficient, electrical resistivity, thermal conductivity and Hall effect measurements were performed at room temperature and up to 600 °C on selected samples. Highp‐type mobilities were measured and a maximum of about 1380 cm2.V−1 .s−1was measured on a sample with a carrier concentration of 7.1×1018cm−3.N‐type samples have substantially lower mobilities but very large Seebeck coefficients. A bandgap of 1.18 eV was estimated from high temperature electrical resistivity and Hall effect measurements. The hole and electron effective masses were also estimated. Based on the experimental data obtained, the potential of IrSb3as a thermoelectric material is discussed. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46824

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

This paper describes the thermoelectric properties of Fe1−yCrySr2ribbons and bulks fabricated by spin‐casting and usual casting. The thermoelectric powers, the electrical resistivities, the power factors of the ribbons and the bulks were measured, and the X‐ray diffraction patterns, the scanning electron microscopic images were observed. The thermoelectric powers, the electrical resistivities and the power factors of the ribbons and the bulks fory=0∼0.7 become large after annealing. The thermoelectric power, the power factor of the annealed ribbon are larger than those values of the annealed bulk fory=0∼0.7. The annealed ribbons consist of the &bgr; phase fory≤0.07, and of the &bgr; phase and the CrSi2phase for 0.07<y≤0.7. With increasingybelowy=0.07, the thermoelectric power and the electrical resistivity become small because of increase in hole density in the &bgr; phase. With increasingyfrom 0.07 to 0.1, the thermoelectric power and the electrical resistivity become large because hole density decreases with the appearance of the CrSi2phase in the &bgr; phase. Abovey=0.1, the thermoelectric power and the electrical resistivity decrease gradually with increasing the amount of the CrSi2phase. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46845

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Based on literature data and experimental findings at the Jet Propulsion Laboratory (JPL), semiconductors with the skutterudite structure TPn3(where T is a transition metal element such as Co, Rh, Ir, Ni, and Pd, and Pn is a pnicogen element such as P, As, and Sb) possess attractive characteristics and show a good potential for highZTvalues. The high degree of covalency results in high mobility and low electrical resistivity values while a relatively complex 32 atom unit cell results in a reasonably low thermal conductivity. Bothn‐type andp‐type electrical conductivity samples have been obtained. Room temperature Seebeck coefficient values up to 200 &mgr;VK−1forp‐type and up to −600 &mgr;VK−1forn‐type have also been measured on several of these materials. In addition, the large number of isostructural compounds, solid solutions and related phases offer many possibilities for optimization of the transport properties to a specific temperature range of thermoelectric applications. By replacing the transition metal or the pnicogen atom by two of its neighboring elements and ensuring that the number of valence electrons is retained, many ternary phases can be successfully derived from the original CoAs3skutterudite structure. Some of these materials were found to have substantially lower thermal conductivities compared to those of the binary compounds. The composition, band gap and doping level can be tailored to achieve maximum performance. An overview of the results obtained to date is provided and our approach to achieving highZTmaterials are discussed in this paper. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46831

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The thermopower and resistivity of MexSi1−x(Me=Fe, Ir and Re) thin films have been investigated with compositions in the vicinity and outside of the stoichiometry of the corresponding semiconducting silicides.Insitumeasurements up to 1100 K give insight into crystallization processes during annealing of the as‐deposited amorphous films. Outside the stoichiometric compositions systematic changes of the thermopower on composition have been found, which are discussed on the basis of results from phase analysis. The behavior of the Re‐Si films is different in comparison with the other two systems because of the high degeneracy of the corresponding silicide ReSi2. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46832

出版商:AIP    

年代:1994

数据来源: AIP