摘要:

The maximum achievable compositional variation in pseudobinary systems can be calculated following a method reported in this work. Preliminary data are shown about a synthesis method based on the recrystallization by moving the quenched melt in a thermal gradient. This method produces ingot with large grains, no compositional gradient and very small number of pores (<1% of the total volume). ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46833

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The spectral dependencies of the optical absorption coefficient of Pb0.995Sn0.005Se:Na in the Hall concentration range from 1.6⋅1019to 1.9⋅1020cm−3atT=300 K have been investigated. The additional absorption bands connected with optical charge transfer processes of the quasi local states were revealed. The single electron energy levels position whereby these processes could be described were estimated. It is shown that the Fermi energy pinning in the Pb1−xSnxSe (x≤0.02) diluted solid solutions could be effected by charge transfer of the intrinsic defects which are the centers with the negative correlation energy. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46834

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Large single crystals of the compound CoSb3were grown from antimony rich melts by the Bridgman gradient freeze technique. CoSb3has the skutterudite crystal structure and a peritectic decomposition temperature of 873 °C. Samples were characterized by X‐ray diffractometry, microprobe analysis and density measurements. A Debye temperature of 306 K was calculated from speed of sound measurements. As‐grown CoSb3crystals showp‐type conductivity.N‐type samples were obtained over a wide range of doping level by addition of Te. Seebeck coefficient, electrical resistivity, thermal conductivity and Hall effect measurements were performed between room temperature and 500 °C. The results of these measurements are presented and discussed. Exceptionally high Hall mobilities were obtained onp‐type samples which is consistent with the high degree covalency of the skutterudite crystal structure. A maximum room temperature Hall mobility of 3445 cm2.V−1.s−1was measured on a sample with a carrier concentration of 4×1017cm−3.N‐type samples were found to have substantially lower Hall mobilities in the range of temperature investigated. A bandgap of 0.55 eV was calculated from the 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 CoSb3as a thermoelectric material is discussed. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46835

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We report on the thermoelectric properties of porosity controlledp‐type SiC/B4C system for thermoelectric devices. Measurements of electrical resistivity, thermoelectric power and thermal conductivity were made on 2 wt. % B4C doped SiC as a function of PSS (Poly‐SilaStyrene) concentration over the range 0.5 wt. %∼25 wt. %. We have shown that room temperature value of thermoelectric figure of meritZof SiC/B4C system can be improved by a factor of 103by the addition of PSS. At higher temperatureZis expected to approach to that of a practical system such as Bi2Te3system. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46836

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A survey was conducted of several alloy systems identified as having certain properties thought to be desirable in high figure‐of‐merit thermoelectric materials. The systems examined include the cerium and lanthanum borocarbides, yttrium nitrides, osmium silicides, and titanium sulfides. Various approaches to the preparation of these alloy systems were explored including vapor transport, arc melting, and mechanical alloying. Among these systems, the borocarbides were found to exhibitp‐type conductivity but generally suffered from relatively high carrier concentrations (on the order of 1021/cm3) and low mobilities (≤10 cm2/V‐s). Both carbon and sulfur dopants produced the highest figure of merit (0.13×10−3/ °C) in the yttrium nitride system at room temperature. Excess silicon was observed to increase carrier concentration and Hall mobility in osmium disilicide while additions of chromium were observed to stabilize the OsSi2crystal structure. Electrical power factors comparable to state of the art silicon‐germanium alloys were achieved in titanium disulfide, however, the electrical transport properties were found to be critically dependent upon the amount of excess Ti in Ti1+xS2. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46837

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The external parameters geometry and frequency of a planetary ball mill were adjusted in order to minimize the duration of mechanically induced Si‐Ge alloy formation. Experimental results were compared with theoretical calculations on impact energies and milling power. It was found that a planetary ball mill with a ratio of the planetary to the system wheel’s frequency of −3 delivers the best milling performance for vial sizes between 0.2 and 0.33 that of the system wheel size. Microstructural investigations on powder compacts revealed that a solid state diffusion mechanism of Ge into the harder Si seems to be the responsible process for realizing a homogeneous Si‐Ge alloy. Crystallite sizes of the processed powders were 30 nm. The knowledge of the influence of external milling parameters on the comminution and alloying behavior of substances and the resulting internal structure of the processed ingots may help in a future correlation between thermoelectrical properties and microstructure. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46851

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Thermoelectric phenomena in anisotropic materials have some specific features which can be used in a number of applications. In our report we will briefly consider physical principles of the anisotropic thermoelectric material applications and will give a short review of the thermoelectric properties of these materials. The possible fields of the applications of the anisotropic devices are discussed and some parameters of these devices are estimated. The analysis shows that the experimental data only on a limited number of materials with large anisotropy of the thermoelectric parameters are available in the literature. On the other hand a plenty of compounds with anisotropic structures which can exhibit anisotropic thermoelectric properties have not been systematically studied. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46838

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Certain of the materials with strong electron‐phonon interaction is studied. These materials are semiconductors with polaron type hopping conduction mechanism; materials with incommensurate structure and natural regular system of energy barriers; semiconductors and semimetals with mobility edge. It is shown that in some cases mentioned types of materials can be rather perspective as thermoelectrics and they can be the base for a new generation of thermoelectrics. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46840

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

IrSb3is a compound of the skutterudite family of materials now being investigated at the Jet Propulsion Laboratory (JPL). A combination of experimental and theoretical approaches has been recently applied at JPL to evaluate the potential of several thermoelectric materials such asn‐type andp‐type Si80Ge20alloys,n‐type andp‐type Bi2Te3‐based alloys andp‐type Ru2Ge3compound. The use of a comprehensive model for the thermal and electrical transport properties of a given material over its full temperature range of usefulness is a powerful tool for guiding experimental optimization of the composition, temperature and doping level as well as for predicting the maximumZTvalue likely to be achieved. Expressions for all the transport properties of thermoelectric semiconductors were derived from the Boltzmann’s transport equation, using the relaxation time approximation. This widely used method has been employed with Fermi statistics to calculate carrier mobility, electrical conductivity, carrier concentration, Hall coefficient, Seebeck coefficient, electronic and bipolar contribution to the thermal conductivity as well as other transport coefficients inp‐type IrSb3. The effect of minority carrier conduction was taken into account and the two most common carrier scattering mechanisms usually necessary to describe the transport properties in these heavy doping conditions were selected—acoustic phonon scattering and ionized impurity scattering. Determination of the lattice thermal conductivity of IrSb3was conducted by considering phonon–phonon, carrier–phonon, and point defect scattering mechanisms. Calculations for the introduction of resonant scattering impurities and ultrafine inert scattering centers have also been performed to evaluate possible additional improvements inZT. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46841

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We report on the temperature dependence of thermoelectric properties ofp‐type SiC/B4C system for thermoelectric devices. Measurements of electrical resistivity, thermoelectric power and thermal conductivity were made on SiC as a function of both B4C doping concentration over the range 0.2%∼60 wt. % and temperature over the range from room temperature up to 600 °C. The figure of merit increases from 2 to 5 decades with temperature increase from room temperature to 600 °C. We conclude that the SiC/B4C system with around 10% of B4C is a promising candidate for thermoelectric applications in the temperature range 400∼600 °C. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46842

出版商:AIP    

年代:1994

数据来源: AIP